WATER POLLUTION CONTROL RESEARCH SERIES
11022 DWU 08/70
Combined Sewer
Regulation and Management
A Manual of Practice
5. DEPARTMENT OF THE INTERIOR • FEDERAL WATER QUALITY ADMINISTRATION
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results and progress
in the control and abatement of pollution of our Nation's Waters. They provide a
central source of information on the research, development and demonstration
activities of the Federal Water Quality Administration, Department of the Interior,
through in-house research and grants and contracts with the Federal, State, and
local agencies, research institutions, and industrial organizations.
Triplicate tear-out abstract cards are placed inside the back cover to facilitate
information retrieval. Space is provided on the card for the user's accession number
and for additional key words. The abstracts utilize the WRSIC system.
Water Pollution Control Research Reports will be distributed to requesters as
supplies permit. Requests should be sent to the Project Reports System, Office of
Research and Development, Department of the Interior, Federal Water Quality
Administration, Washington, D. C. 20242.
Previously issued reports on the Storm & Combined Sewer Pollution Control
Program:
11020
11030
11020
DNS
EXV
12/67
01/69
07/69
11020 FKI 01/70
11020
11020
11020
H020
11020
11023
11020
11020
11023
11020
11020
11024
11034
11024
11024
11000
DIH
DBS
DIG
EKO
-
FDD
-
DGZ
DPI
DWF
FKL
FKN
DMS
—
06/69
06/69
08/69
10/69
10/69
03/70
06/69
10/69
08/69
03/70
12/69
06/70
07/70
11/69
05/70
01/70
Problems of Combined Sewer Facilities and Overflows,
1967.(WP-20-11)
Water Pollution Aspects of Urban Runoff. (WP-20-15)
Strainer/Filter Treatment of Combined Sewer Overflows.
(WP-20-16)
Dissolved Air Flotation Treatment of Combined Sewer
Overflows. (WP-20-17)
Improved Sealants for Infiltration Control. (WP-20-18)
Selected Urban Storm Water Runoff Abstracts.
(WP-20-21)
Polymers for Sewer Flow Control. (WP-20-22)
Combined Sewer Separation Using Pressure Sewers.
(ORD-4)
Crazed Resin Filtration of Combined Sewer Overflows.
(DAST-4)
Rotary Vibratory Fine Screening of Combined Sewer
Overflows. (DAST-5)
Sewer Infiltration Reduction by Zone Pumping.
(DAST-9)
Design of a Combined Sewer Fluidic Regulator.
(DAST-13)
Rapid-Flow Filter for Sewer Overflows.
Combined Sewer Overflow Seminar Papers.
Control of Pollution by Underwater Storage.
Combined Sewer Overflow Abatement technology.
Storm Water Pollution.
Storm Pollution & Abatement from Combined Sewer
Overflows-Bucyrus, Ohio. (DAST-32)
Engineering Investigation of Sewer Overflow
Problem—Roanoke, Virginia.
Storm & Combined Sewer Demonstration Projects-
January 1970.
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COMBINED SEWER REGULATION AND MANAGEMENT
•5^
A MANUAL OF PRACTICE
by the
American Public Works Association
for the
FEDERAL WATER QUALITY ADMINISTRATION
DEPARTMENT OF THE INTERIOR
and
TWENTY-FIVE LOCAL GOVERNMENTAL JURISDICTIONS
Program No. 11022 DMU a -
Contract 14-12-456
July 1970
For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington, D.C., 20402 - Price $t.50
EERU-T1X
RECEIVED
APR 51989
EERU-TIX
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SPONSORING LOCAL AGENCIES
City of Akron, Ohio
City of Alexandria, Virginia
City of Atlanta, Georgia
City of Boston, Massachusetts
Metropolitan District Commission, Boston, Massachusetts
City of Charlottetown, PEI, Canada
Metropolitan Sanitary District of Greater Chicago, Illinois
City of Cleveland, Ohio
City of Eugene, Oregon
City of Fort Wayne, Indiana
City of Kansas City, Missouri
City of Middletown, Ohio
City of Montreal, Quebec, Canada
City of Muncie, Indiana
Metropolitan Government of Nashville and Davidson County, Tennessee
City of Omaha, Nebraska
City of Owensboro, Kentucky
Allegheny County Sanitary Authority, Pittsburgh, Pennsylvania
City of Richmond, Virginia
Metropolitan St. Louis Sewer District, Missouri
City of St. Paul, Minnesota
Municipality of Metropolitan Seattle, Washington
City of Syracuse, New York
City of Toronto, Ontario, Canada
Washington, District of Columbia
FWQA Review Notice
This report has been reviewed by the Federal Water
Quality Administration and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies of the
Federal Water Quality Administration.
-XI V-J.; :;"t j,3
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ABSTRACT
Design application, operation and maintenance of
combined sewer overflow regulator facilities are
detailed in this Manual of Practice, developed in
conjunction with a report prepared on combined
sewer overflow regulators.
Design calculations are given for various types of
regulators and tide gates. A sample regulator facility
control program is given to illustrate the development
of a control system. Operation and maintenance
guidelines are also given. Thirty-eight sketches and
photographs are included.
This manual and accompanying report were
submitted in fulfillment of Contract 14-12-456
between the Federal Water Quality Administration,
twenty-five local jurisdictions and the American
Public Works Research Foundation.
111
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APWA RESEARCH FOUNDATION
Project 68-lb
STEERING COMMITTEE
Peter F. Mattel, Chairman
Arthur D. Caster Walter A. Hurtley
William Dobbins Ed Susong
George T. Gray Harvey Wilke
Carmen Guarino
Richard H. Sullivan, Project Director
J. Peter Coombes, Principal Investigator
SPECIAL CONSULTANTS
James J. Anderson
Dr. Morris M. Cohn
Morris H. Klegerman
Ray E. Lawrence
M. D. R. Riddell
R. D. Bugher
R. H. Ball
Leo Weaver
Lois V. Borton
Marilyn L. Boyd
Kathryn D. Priestley
Patricia Twist
APWA Staff*
Violet Perlman
Katherine Manolis
Ellen M. Pillar
Maxine Coop
Mary J. Webb
Sheila J. Chasseur
Oleta Ward
*Personnel utilized on a full-time or part-time basis on this project
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CONTENTS
ABSTRACT i
In Explanation: The Purpose of a Manual
of Practice on Combined Sewer
Regulation and Management xi
SECTION 1
Types of Regulators; Basic Principles;
Applicability; Guidelines on Selection 1
SECTION 2
Design Guidelines for Regulators, Their
Chambers and Control Facilities 19
SECTION 3
Design Guidelines for Tide Gates, Their
Chambers and Control Facilities 79
SECTION 4
Instrumentation and Control
of Regulator Facilities 93
SECTION 5
Practices for Improved Operation and Maintenance
of Regulators and Their Appurtenances 107
SECTION 6
Design and Layout, as Influenced by Operation
and Maintenance — Typical Criteria and Detafls 113
SECTION 7
Example of Systems Control Through Instrumentation 121
SECTION 8
Acknowledgements 133
Vll
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FIGURES
1 122 1
I 1222
1.12.2.3
1.12.3
1.12.4
1.12.5
1.12.6
1.12.7
2.1.1
2.1.3.1
2.1.3.2
2.1.3.3
2.3.3.1
2.3.3.2
2.5.1.1
2.5.2
2.6.1
2.7.1
2.7.3
2.8.1.1
2.8.1.2
2.8.1.3
2.8.2
2.8.3
2.8.4.1
2.8.4.2
2.8.4.3
2.9.1
2.10.1.1
2.10.1.2
2.10.1.3
Diagram of Fluidic Regulator ,
Vortex Element
Schematic Arrangement— Fluidic Interceptor
Sewer Flow Control— Single Sensor
Vortex Regulators .
Spiral Flow (Helical) Regulator
Possible Application, Stilling Pond Regulator
Possible Application High Side-Spill Weir
Artist's Conception Inflatable Fabric Dam
Typical Layout, Manually Operated Gate
Hydraulic Profile, Manually Operated Gate (2 cfs) , .
Flow Through 12-Inch-Wide Orifice
Hydraulic Profile Manually Operated Gate (3 .3 cfs)
Hydraulic Profile Horizontal Orifice Regulator (2 cfs)
Hydraulic Profile Horizontal Orifice Regulator (4.3 cfs) .....
Side-Overflow Weir for Small Overflow
Acker's Method Factor for Side-Spill Weir Design
Internal Self-Priming Siphon
Typical Layout Float-Operated Gate . . .
Hydraulic Profiles Float-Operated Gate
Typical Layout Tipping Gate Regulator . . . . . .
Tipping Gate Used at Milwaukee
Tipping Gate Used by Allegheny County Sanitary Authority . . .
Calibration of 12-inch Control Gate
Activation of Free Floating 12-Inch Tipping Gate
Hydraulic Conditions for Tipping Gates
Hydraulic Profile for 2-cfs Tipping Gate Regulator
Hydraulic Profile for 2.45-cfs Tipping Gate Regulator
Applications of Cylindrical Gates
Cylinder-Operated Gate
Cylinder-Operated Gate (Water Actuated)
Cylinder-Operated Gate (Oil Actuated)
Page
8
9
..'... 10
11
13
14
15
17
22
25
26
28
32
34
36
39
40
. .... 42
45
. •. . . . 52
53
. .... 54
55
56
58
59
61
63
65
66
67
IX
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2.10.4 Hydraulic Profile for Regulator With
Cylinder-Operated Gate
2.12.1 Ponsar Siphon
3.1.3.1 Cast Iron Circular Flap Gates
3.1.3.2 Square and Rectangular Cast Iron Flap Gates
3.1.3.3 Circular Pontoon Flap Gates
3.1.3.4 Square and Rectangular Pontoon Flap Gates
3.1.3.5 Square and Rectangular Timber Flap Gates
3.2.1 Plan and Profile of Tide Gate Chamber . .
3.2.2 Flap Gates Head Loss Coefficients ....
6.1.3 Access Stairs
69
74
82
83
84
85
86
89
90
116
TABLES
6.1.6 Sluice Gate Sizes 118
6.2 Sluice Gate Materials
119
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IN EXPLANATION: THE PURPOSE OF A MANUAL OF PRACTICE
ON COMBINED SEWER REGULATION AND MANAGEMENT
The American Public Works Association has
completed a research study covering a national
in-depth investigation of combined sewer practices of
representative local jurisdictions. The study covered
the design, choice and application of regulator
devices, use of tide or backwater gate facilities,
performance of regulator-overflow installations, and
operation and maintenance methods. Efforts were
made to obtain reliable information on the cost of
construction, equipment, and maintenance of
regulators and their appurtenant facilities. The report
of this investigation covers the methods utilized in
the survey, an evaluation of the research data, an
enumeration of the findings and a list of
recommendations. The recommendations when
adopted should result in better engineering
technologies and the utilization of more sophisticated
methods and mechanisms in future regulator practice.
The investigation disclosed the inadequacies of
many of the present regulator-overflow devices, and
methods of their operation. Wet-weather overflows
were, as expected, common to all installations;
however, these overflows were more frequent and
more extended in duration than necessary to protect
upstream collector sewers, and downstream
interceptors and treatment works. Even instances of
dry-weather overflows were reported. Little or no
attempt has been made to improve the quality of
overflow waste waters by the use of supplementary
protective devices.
The major deficiencies, unreliability and
inadequacy of regulator-overflow installations, in the
main, were the result of failure to apply recognized
engineering and construction methods. These
malpractices included such matters as: Lack of overall
planning of combined sewer systems and of
recognition that overflow regulation is a total systems
problem; the use of an excessive number of overflow
points to protect local sewer systems from
surcharging and backflooding, without considering
the impact of any single regulator-overflow station on
a total system network and on the pollution of
receiving waters; inexact design criteria for such
facilities; inappropriate choice and application of
particular types of regulators to the specific control
functions; and ineffective operation and maintenance
procedures.
It is apparent that many of these positive factors
resulted from cut-and-try design, and operation
techniques utilized during the years when combined
sewer flows were discharged to receiving waters
without treatment. The advent of sewage treatment,
coupled with higher standards of pollution control of
receiving waters, now make it mandatory to utilize
improved practices in combined sewer regulation.
These improvements in regulator technologies are
of practical importance. The engineering profession
and government officials must face the responsibility
of providing for the control of combined sewer
overflows at the lowest possible cost commensurate
with dependable, performance and the reduction in
pollution discharged to receiving waters.
These purposes can be enhanced by establishing
construction, equipment, and maintenance criteria,
which will serve as functional guidelines for designers
of combined sewer systems; owners of such sewer
facilities; manufacturers who provide the equipment
for regulator and sewer system .management
procedures; and operation and maintenance personnel
who must get the best possible service from the best
possible facilities.
It is the purpose of this Manual of Practice on
Combined Sewer Regulation and Management to
present guidelines for:
1. Applicability of types of regulators to meet
. specific control needs (Section 1)
2. The design and layout of regulator structures
and regulator devices and controls (Section 2)
3. Design of tide or backwater gate devices and
structures (Section 3)
4. The application of instrumentation and
control facilities for the purpose of achieving
maximum performance from each individual
regulator station and of the integration of all
regulator stations into a total controlled systems
management program (Section 4)
5. Improved operation and maintenance
practices (Section 5).
This Manual of Practice is not intended to be a
"cookbook." It offers guidance to the design
engineering profession; to manufacturers and
suppliers of products and processes of primary and
secondary significance to the regulator fields; and to
governmental agencies and officials who are
responsible for the administration and operation of
combined sewer systems. The Manual is not a
substitute for knowledge and experience. It is a tool
for the use of properly trained and experienced
professionals.
XI
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SECTION 1
TYPES OF REGULATORS; BASIC PRINCIPLES;
APPLICABILITY; GUIDELINES ON SELECTION
CONTENTS
STATIC REGULATORS
Page
1.1 Manually Operated Gates 3
1.2 Fixed Orifices (Vertical) - - - 3
1.2 Fixed Orifices (Horizontal) - the drop inlet 3
1.4 Leaping Weirs 4
1.5 Side-Spill Weirs 4
1.6 Internal Self-Priming Siphons . . . . 4
DYNAMIC REGULATORS - SEMI-AUTOMATIC
1.7 Float Operated Gates 5
1.8 Tipping Gates 5
1.8 Cylindrical Gates 5
DYNAMIC REGULATORS - AUTOMATIC
1.10 Motor-Operated Gates 6
1.11 Cylinder-Operated Gates 6
1.12 Current Developments - New Devices 6
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STATIC REGULATORS
1.1 Manually Operated Gates
1.1.1 Basic Principle
The, chief element of this regulator is a manually
operated vertical gate mounted on a vertical orifice,
through which passes the intercepted sewage which is
diverted to the treatment plant. Low flows pass
through the gage, a channel with either subcritical or
critical depth. At higher flows the regulator may act
as a simple vertical orifice with free discharge or as a
submerged orifice.
The regulator structure consists of an overflow
dam constructed across the channel of the combined
sewer which diverts dry-weather flow through the
gate into an orifice chamber. From this chamber the
flow is conveyed by a branch interceptor to the main
interceptor. In wet weather, excess flows discharge
over the dam to the receiving waters.
1.1.2 Application
This device may be used for diverting
wet-weather flows of less than 4 cfs. since dynamic
regulators rarely are justified economically for such
small flows. Manually operated gates are considered
more effective as regulators than other types ofstatic
devices. The gate opening is adjustable so that the
quantity diverted to the interceptor may be varied.
Operation and maintenance costs, as well as
construction costs, are less for this type than for
automatic regulators. It is most applicable where
further regulation of the diverted flow ^will occur
downstream, either at another regulator or at the
treatment plant.
For flows of less than 4 cfs the choice of
regulator would appear to be between the manually
operated gate and the tipping gate described in 1.8.
However, the latter device diverts a lower ratio of
wet-weather to dry-weather flow.
1.2 Fixed Orifices-Vertical
1.2.1 Basic Principle
The main element is a fixed vertical opening in
the combined sewer through which the diverted flow
passes. The principle is as described for the manually
operated gate.
1.2.2 Application
This device is generally used for wet-weather
flows of less than 2 cfs. It is specifically applicable
where additional regulation of the diverted flow will
occur further downstream, either at another regulator
or at the treatment plant. When not regulated
downstream, the intercepted flow during a storm may
exceed design quantity. When used for small flows,
such excess interception may not be serious in a large
sewer system where only a small percentage of the
total flow is diverted to the plant.
The use of a manually operated gate is preferred
over a fixed orifice, although the gate represents an
additional capital cost.
While provision can be made in design for varying
the size of the fixed orifice by the use of removable
plates, the changing of such plates may be difficult
after the regulator has been in service for some time.
The fixed orifice does not require lubrication as does
the manually operated gate.
1.3 Fixed Orifices-Horizontal
(The Drop Inlet)
1.3.1 Basic Principle
The device consists of a horizontal opening
constructed either in the bottom of the combined
sewer or the bottom of a separate chamber of the
combined sewer. In the former case it is usually
covered with a grate. When constructed in a separate
chamber a diversion dam must be constructed in the
combined sewer to divert the dry-weather flow
through a vertical opening into the orifice chamber. It
is also preferable to use such a dam when the orifice
is placed in the combined sewer. In this way the
opening acts as a horizontal orifice under all
conditions of flow. The flow not diverted into the
interceptor through the orifice passes over the dam to
the receiving waters.
1.3.2 Application
This device is generally used for diverting
wet-weather flows of less than 2 cfs. Present practice
is to replace this type with more effective regulators.
During dry-weather periods, in spite of daily
maintenance, clogging of the grates frequently causes
excessive overflow to the receiving waters. During
storm periods, clogging of the grates, or "jumping
across" the orifice, causes a. large portion of the total
flow to discharge to overflow.
Maintenance is difficult as it is impossible to shut
off all flow to the interceptor unless the horizontal
orifice is placed in a separate chamber. When a
separate chamber is used, a vertical orifice will result
in less variation in intercepted flows during storm
periods than is the case in a horizontal orifice.
The only advantages of this type of regulator are
its low initial capital cost and that, at most, only one
structure is required.
The horizontal orifice does not regulate
combined sewer flows effectively and is expensive to
maintain.
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1.4 Leaping Weirs
1.4.1 Basic Principle
This regulator consists of an invert opening in the
combined sewer dimensioned to permit the
dry-weather flow to fall through the opening and to
be conveyed through a branch interceptor to the
main interceptor and treatment plant. During wet-
weather periods the increase in velocity and depth in
the combined sewer causes all or most of the flow to
pass over or leap over the opening and continue on to
receiving waters.
1.4.2 Application
Leaping weirs generally have been used for
intercepting low volume flows. While used to a
considerable extent in the past, recent practice is to
replace existing leaping weirs with other types of
regulators.
The disadvantages of this regulator are:
1. It cannot be used when a tide gate is required
since the backwater effect will prevent the
leaping action and the device will act as a
horizontal orifice.
2. During storm periods all the flow may leap
over the opening and part of the flow will not be
diverted to the treatment plant.
3. It is difficult, if not impossible to
temporarily shut off all flow to the interceptor
and treatment plant.
4. The opening may become clogged or bridged
with floating material, causing spillage of
dry-weather flow into the receiving waters.
Its main advantage is that only one structure is
required, which may be desirable where space is
limited or where economy is essential. The leaping
weir is not considered an effective regulator.
1.5 Side-Spffl Weirs
1.5.1 Basic Principle
The side-spill weir is constructed parallel to, or at
a slight angle to the axis of the combined sewer, with
the crest set at an elevation above the peak
dry-weather flow line. During wet-weather periods
flows in excess of the peak dry-weather flow will
discharge over the weir into the outfall sewer. The
excess flow may be further regulated downstream or
may discharge directly into the receiving waters.
7.5.2 Application
Theoretically, the side-spill weir may be used for
the overflow of any quantity of excess wet-weather
flow. However, since the length of the weir is
proportional to the quantity of overflow, the
structure becomes larger and more costly as the
volume of overflow increases. Side-spill weirs are
frequently used for low flows, and where the
overflows are regulated further downstream.
The major advantage of this type of regulator is
that maintenance costs are generally fower than for
other types. The major disadvantage is that the
regulator cannot be adjusted after construction
except by reconstruction of the weir or by manual
adjustment of the weir crest.
When close regulation of the flow to the plant is
desired it is preferable to use other types of
regulators, the design of which is based on accepted
hydraulic principles. Little or no field data have been
published regarding the operation of these weirs that
conform with the theoretical values for larger flows.
Where such regulation farther downstream does not
take place the intercepted flow in tunes of storm may
exceed interceptor design capacity. This should be
checked in design to insure that such excess
interception does not result in unnecessary spills at
outfall locations downstream or cause surcharging at
the treatment plant.
1.6 Internal Self-Priming Siphons
1.6.1 Basic Principle
A siphon may be defined as a closed conduit
which lifts a liquid to an elevation higher than its free
surface and discharges it at a lower elevation. When a
closed conduit rises above the hydraulic grade line,
negative pressure (i.e., pressures less than atmospheric
pressure) develops at the summit which is equal to
the vertical distance between the hydraulic grade line
and the center line of flow at the summit. To initiate
operation the siphon must be primed, i.e., sufficient
negative pressure must be developed at the summit to
raise the water in the uptake branch of the siphon
until flow is established. Priming is effected by
removal of air from the summit either by mechanical
means, such as a vacuum pump, or by use of the
hydraulic energy inherent in the differential in
elevation between the upper and lower water surfaces
of the intake and discharge levels of the siphon. This
difference in levels is the operating power which must
overcome all energy losses within the siphon,
including friction, entry, bends, and discharge; it
generates the required velocity to maintain the design
flow rate. Under maximum vacuum conditions in a
siphon, a water column could rise to a theoretical
height of approximately 34 feet at mean sea level.
Practically, a water column height of only 75 percent
of the theoretical maximum can be obtained.
7.6.2 Application
The internal self-priming siphon may be used to
divert excess storm flows to receiving waters and not
to the interceptor as the normal regulator practice
dictates. Such flows should exceed about 5 cfs so that
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the throat section will be large enough to prevent
clogging. It may be used to replace an overflow weir
in any regulator, provided there is an adequate
difference in water levels above and below the siphon
to allow it to function as designed. In some cases the
siphon may be more economical than a weir due to
the smaller structure required. This type siphon also
can be used to control the water levels in a conduit
leading to a treatment plant or pumping station in
order to prevent excessive flows to these installations.
The siphon will maintain the water levels within a
narrow range by discharging excess flows to receiving
waters. For this purpose it may be desirable to use
two or three siphons, with each succeeding one set to
operate at a slightly higher water level.
DYNAlVflCREGUIATORS-SEMI-AUK»lAIIC
1.7 Float-Operated Gates
1.7.1 Basic Principle
This type regulator consists of a regulating gate, a
float, and an .interconnecting device arranged so that
variations in the water level either in the combined
sewer or interceptor will move the float and actuate
the gate. Operation of the gate does not require either
hydraulic pressure or electric power. A typical layout
is shown in Figure 2.7.1.
The regulator consists of an overflow dam or weir
constructed across the channel of the combined sewer
to divert dry-weather flow through the regulating gate
into the regulator chamber and thence into the
branch interceptor. The branch interceptor discharges
the diverted flow into an interceptor which conveys
the flow to the treatment plant. In wet weather
excess flows discharge over the dam and continue
through the storm sewer to the receiving waters.
1.7.2 Application
Theoretically, this type device can be used for
diversion of any volume. Generally, however, its use
will not be economically justified for diverting flows
of less than 4 cfs. Its major advantage is that no
outside source of energy is required for operation.
Regulation is controlled by movements of the float.
In the larger sizes, the float diameter may be as much
as 5 feet. This requires a large size floatwell which
niay trap grit that creates a maintenance problem.
Accumulation of floating material on the float may
cause malfunctioning of the system. Since the entire
system is in fine balance, proper operation requires at
least biweekly maintenance.
1.8. Tipping Gate
1.8.1 Basic Principle
This regulator consists of a rectangular metal
plate mounted on a horizontal pivot located below
the center of gravity of the plate. The plate is
mounted in a casting in such a manner that the flow
diverted to interceptor must pass under it. During
dry-weather flows the pressure on the upstream side
of the gate is below the pivot and the gate rests in the
open position permitting all flow to pass into the
interceptor. During periods of storm flow the water
level in the combined sewer rises and the resultant
pressure on the upstream side of the gate above the
pivot causes the gate to partially close, thus reducing
the orifice area and limiting the quantity of flow to
the interceptor. The remainder of the storm flow
discharges over a diversion dam into the outfall sewer
and into the receiving waters.
1.8.2 Application
Tipping gates can be used to divert a wide range
of flow volumes. These gates will intercept less flow
in wet-weather periods than the fixed orifice or
manually operated gate due to the partial closing or
"tipping" of .the gate by the upstream water pressure.
The device can be adjusted in the field to revise either
the maximum or the mihimum opening, thus altering
the flow to be intercepted. The discharge through a
12-inch gate under a head of one foot will vary from
about 1 to 6 cfs depending on the opening height.
The head required to close the gate will vary from 0.3
to 1.5 feet, depending upon the downstream water
level.
1.9 Cylindrical Gates
1.9.1 Basic Principle
This device consists of a horizontal circular
orifice located in a chamber adjacent to the combined
sewer. The regulator is a cylindrical gate balanced by
a counterweight and hung from an articulated frame
directly over the orifice.
The rising of the water surface, either in the
collector or in the interceptor, controls directly the
closing of the orifice by the cylinder without the use
of floats and:transmissions.
1.9.2 Application
This new type regulator has been used in only
one city for sewage diversion. Operation 'and
maintenance problems are still being worked out.
Further performance records are needed for accurate
evaluation. This gate is hydraulically activated by
sewage flow and, hence, no outside source of energy
is required. According to the manufacturer this device
is suitable for diverted flows of from less than 10 cfs
to 200 cfs.
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DYNAMIC REGULATORS-AUTOMATIC
1.10 Motor-Operated Gate
1.10.1 Basic Principle
This regulator functions in similar fashion to the
cylinder-operated gate (1.11) except that the gate is
operated directly by a motor rather than a pneumatic
or hydraulic cylinder.
1.10.2 Application
The motor-operated gate can be used for any
volume of flow where automatic or remote control of
the diverted flow is desired. Its use is not generally
considered economically feasible for design flows of
less than 4 cfs. Electric power must be available for
operation of the motor. The motor is mounted on a
floor stand directly above the gaje.
If the sewer is deep enough the motor can be
housed in an underground chamber; otherwise the
motor will require housing above the ground. The
latter alternative is preferable in any case since
corrosion is less in an above-grade site. If an
underground chamber is used, dehumidification and
heating equipment may be provided or special
equipment may be provided to handle these difficult
conditions.
1.11 Cylinder-Operated Gate
1.11.1 Basic Principle
The chief element of this regulator is a
cylinder-operated gate and orifice through which the
intercepted flow passes to the treatment facility. The
gate is operated by a hydraulic or pneumatic cylinder
which responds to the sewage level as measured by a
sensing device located either upstream or downstream
of the gate. Operation of the cylinder may be by
water, oil or air pressure. The sensor usually is either
a float or compressed-air bubbler tube. The gate also
may be operated by remote control which overrides
the sensing device.
The regulator consists of an overflow dam
constructed across the channel of the combined sewer
so as to divert maximum dry-weather flow through a
sluice gate into a regulator chamber. From this
chamber the flow is conveyed by a branch interceptor
to the main interceptor which leads to the treatment
plant. Excess flows during storm periods will
overflow the dam and continue in the combined
sewer to the receiving waters.
1.11.2 Application
The cylinder-operated gate is suitable for flows
over 4 cfs where automatic regulation of the diverted
flow is desired. While this type can be used on smaller
flows, it is not generally considered economical.
The water-cylinder type can be used where a
water supply is available which will produce a
minimum cylinder pressure of 25 psi. Because of the
low cylinder pressure the size of sluice gate is
generally limited to 9 to 12 square feet. Multiple
gates are used where the opening exceeds 9 to 12
square feet. The hazard of cross-connections between
the cylinder system and the public water supply must
be considered. This is an important design
requirement.
The oil-cylinder type requires an electric power
source to operate the oil pump and the air
compressor. To protect this equipment from the
effects of the sewer atmosphere a separate chamber
must be constructed to house the electrical
equipment. Oil pressure of about 750 psi is preferred.
The gate is not restricted as to size, as in the case of
the water-cylinder type.
The air-cylinder type also requires a source of
electric power to operate the air compressor. Air
pressures of 90 to 200 psi have been used.
In jurisdictions that have tried both types, the
oil-cylinder is preferred. The principal advantage of
the oil-cylinder or air-cylinder type is that the flow
can be monitored and regulated from a remote point
thus making full use of the interceptor system, and its
storage capacity, while protecting downstream
treatment facilities and reducing the frequency and
volume of overflows.
In general, cylinder-operated gates are considered
an effective type of regulator currently in use in
North America.
1.12 Current Developments—New Devices
1.12.1 General
This subsection includes regulators of recent
design on which experimental work has been done
and which, in some cases, have been installed for
actual use.
1.12.2 Fluidics
Fluidics is defined as "the use of devices that
have no moving pajts, and that use a fluid medium
for control of other devices, or that directly achieve
an objective such as logic, computation or
amplification". (Engineer, Jan.-Feb., 1969).
Fluidic devices of two general types have
applicability, depending on the type of fluid-flow
interaction that takes place within them. These
categories are: (1) wall attachment, and (2) vortex
amplifier.
Wall attachment devices form the largest group of
fluidic components. In these devices, a high-velocity
jet of fluid, emitted between two walls, attaches itself
to one of them, attracted there by an area of lower
pressure next to the wall caused by air entrainment.
-------
The jet remains stable in this position unless it is
disturbed by a pressure pulse or by continuous
pressure from a central port. The basic configuration
is shown in Figure 1.12.2.1.
The vortex amplifier consists of a cylindrical
chamber as shown in Figure 1.12.2.2, an axially
oriented outlet, a radially located supply inlet and a
tangentially directed control Met. When the flow is
not being controlled, the inflow proceeds directly
through the chamber to the outlet. When the flow is
controlled, the momentum exchange between the
inflow and control flow establishes a resultant spiral
flow path to the outlet. This centripetal acceleration
can provide significant impedance to the flow and the
variation is essentially proportional to the control
flow in maximum/minimum -ratios up to ten.. The
device, therefore, operates in analog fashion. This
produces quantity control and, as explained in
1.12.3, the secondary velocities imparted in simple
spiral motion may induce solids separation in the
flow. This offers opportunity for the control of the
quality of overflow wastes.
Figure 1.12.2.3 shows a schematic arrangement
for a fluidic regulator. The combined sewer splits into
two branches. The first, or branch interceptor,
conveys the flow to the treatment plant and the
second, the storm sewer, conveys additional flow to
receiving waters. In dry-weather periods a low dam in
the storm sewer diverts all the flow to the branch
interceptor and thence to the treatment plant. In
wet-weather periods the portion of the flow diverted
to each branch can be regulated by the amount of air
pressure or vacuum supplied to slots A and B. These
slots extend the full height of the sewer. The air
pressure or vacuum is self-induced by the flow in the
sewer by the use of various pneumatec devices.
Flow in excess of design cannot be passed
through the regulator device. Excess flow can be
passed over the unit into the overflow channel.
1.12.3 Vortices
The vortex regulator (in England called a vortex
overflow or rotary vortex overflow) consists of a
circular channel in which rotary motion of the sewage
is induced by the kinetic energy of the sewage
entering the tank. Flow to the treatment plant is
deflected and discharges through a pipe at the bottom
and near the center of the channel. Excess flow in
storm periods discharges over a circular weir around
the center of the tank and is conveyed to receiving
waters. It is claimed that the rotary motion causes the
sewage to follow a long path through the channel. In
this period secondary innovational flow patterns are
established, setting up an interface between the fluid
sludge mass and the clearer liquid. In effect, it is
claimed the device acts as a quality separator. The
flow containing the concentration of solids is directed
to the interceptor.
Research has been carried out on hydraulic
models and two full-sized regulators of this type have
been built in Bristol, England, (Reference 1). Details
of these two regulators are shown in Figure 1.12.3.
Design factors for these regulators are as follows:
Whiteladies Road Alma Road
Regulator diameter (ft) 18 18
Overflow diameter (ft) 9 9
Av. dry-weather flow (cfs) 0.18 0.92
Wet-weather flow diverted
to plant (cfs) 2.58 5.84
Ratio WWF:DWF-design 14 6
Storm flow—once a year (cfs) 44.0 54.7
Size inlet (ft) 3 4x3
The ratio of wet-weather flow to dry-weather
flow of 6:1 used in-the Alma Road regulator
conforms with British practice. In the Whiteladies
Road regulator, provision was made for reducing the
ratio if it becomes necessary.
During dry-weather periods sewage enters the
chamber and flows into the branch interceptor near
the center. In storm periods excess sewage discharges
over the center weir and flows out the storm sewer.
The baffle and weir crest configurations prevent
floating material from flowing over the weir.
The depth of the chamber from the weir level to
the invert is dependent on the available head, since
the plant outlet is operating under a hydraulic grade
from the weir level to the point where the sewer
flows free. The storm sewer outlet must pass under
the chamber and, if necessary, the entrance to the
pipe can be surcharged. The design of the overflow
weir follows accepted hydraulic practice and its level
will normally be set so that at maximum design flow
the inlet sewer is full.
Model studies at Bristol using synthetic sewage
solids_ indicated a higher removal of solids in the flow
to the bottom of the regulator than in the flow over
the weir. Pilot studies are now underway at Bristol
using a vortex regulator as a primary clarifier for raw
sewage.
However, another series of experiments elsewhere
on a model vortex regulator using raw sewage
indicated poor performance in removing screenable
solids. Under certain conditions the concentration of
screenings in the sewage over the weir was greater
than in the sewage passing to the bottom of the
regulator (Reference 2).
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FIGURE 1.12.2.1
Courtesy Bowles Fluidic Corp.
-------
FIGURE 1.12.2.2
S
CO
o
s
0
o
10
c
if
CO
Si
VORTEX ELEMENT
Counasy Bowles Fluidic Corp.
-------
FIGURE 1.12.2.3
SCHEMATIC ARRANGEMENT- FLUIDIC INTERCEPTOR
SEWER FLOW CONTROL - SINGLE SENSOR
Courtesy Bowles Fluidic Corp.
10
-------
FIGURE 1.12.3
COMBINED SEWER
STORM SEWER
B
INLET 36"DIA.
AFFLE
BRANCH INTERCEPTOR
TO TREATMENT PLANT
SECTION "A"-"A"
WHITE LADIES ROAD
COMBINED SEWER
INLET 4'X3'
SCUM BOARD
BRANCH.
INTERCEPTOR
SCALE OF FEET
5 10 is
ALMA ROAD
VORTEX REGULATORS
Courtesy Institution of Civil Engineers
11
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1.12.4 Spiral Flow Separators
The spiral-flow regulator (in England the
proposed name for the device is "storm sewage
spiral-flow separator") is based on the concept of
using secondary helical motions which exist in the
bends of conduits, to establish a boundary layer
between concentrated solids-bearing flow and clearer
liquid, thus effectively separating the more heavily
polluted mass for discharge to the interceptor.
Basically, in a bend of a conduit the direction of
flow paths is not circumferential but follows a helical
or spiral pattern. At the bend the more concentrated
liquid mixture is nearer to the bed of the channel and
tends to concentrate along the inner wall of the bend
and the clearer liquid mixture tends to flow out
towards the outer wall. With an overflow positioned
along the outer wall of the bend it is possible to draw
off the less polluted effluent. A bend with a total
angle between 60 and 90 degrees is employed.
Model studies of this device were carried out at
the University of Surrey, England (Reference 3).
These investigations are by no means complete but
they indicate that it is feasible, by one short bend or
a series of short bends, to separate the heavily
polluted sewage from the clearer overflowing liquid.
The simplest form of regulator suggested by the
model studies is shown in Figure 1.12.4. A short bend
of approximately 60 degrees is used as -a separator.
The heavily polluted sewage is drawn to the inner
wall. It then passes to a semi-circular channel situated
at a lower level leading to the treatment plant. The
proportion of the drawn-off discharge will depend on
the particular design. The side weir, with properly
designed baffles, starts 10 to 15 degrees from the
beginning of the bend at the outer wall. Its length will
depend on the design, but it could become a double
weir downstream of the end of the bend, i.e., after
the heavily polluted sewage is decanted or drawn off.
Surface debris collects at the end of-the chamber and
passes over a short flume to join the sewer conveying
the flow to the treatment plant.
The authors of the model study report that even
the simplest application of the spiral-flow separator
will produce a cheap regulator which will be superior
to many existing types. They also stated that further
research is necessary in order to define the variables,
the limits of applications, and the actual limitations
of the spiral-flow regulator.
The principal advantage of this device is that two
relatively flat, reverse curves, produce effective helical
motion which may provide quality separation
characteristics. This application may be economically
significant in existing space-limited combined sewer
interceptor junction locations.
7.72.5 Stilling Ponds
The stilling pond regulator as used in England
comprises a short length of widened channel which
acts as a stilling basin, from the bottom of which the
flow to the plant is discharged. The flow to the plant
is controlled either by use of an orifice on the outlet
in the chamber or by use of a "throttle pipe,"—i.e.,
an outlet pipe designed so that it will be surcharged in
wet-weather periods. Its discharge will depend on the
sewage level in the regulator. Excess flows during
storms discharge over a transverse weir and are
conveyed to the river. The use of the stilling pond
provides time for the solids to settle out when the
first flush of storm water arrives at the regulator
before discharge over the weir begins. In England it is
generally assumed that the first flush will carry the
greatest concentration of solids. This first flush
concept is not universally accepted in North America.
The performance of this regulator was
investigated in England (Reference 2). The
experimental structure is shown hi Figure 1.12.5. The
size of this structure was considered suitable for a
domestic population of 2,000. Discharge to treatment
was 0.9 cfs at first spill over the weir. At maximum
inflow to the regulator of 7.4 cfs the flow to
treatment was 1.06 cfs. Tests were made with no
scum board and with a scum board set 6 and 18
inches from the weir. The best results were obtained
with the scum board set 6 inches from the weir when
the ratio of screenings in the overflow to the
screenings in the flow to the plant was 0.69.
A possible application of this type regulator is
shown in Figure 1.12.5 when it is desired to construct
the chamber in an existing combined sewer.
This type regulator is considered suitable for
overflows up to 30 cfs (Reference 4). If the stilling
pond is to be successful in separating solids it is
suggested that not less than a 3-minute retention be
provided at the maximum rate of flow (Reference 4).
1.12,6 High Side-Spill Weirs
Unsatisfactory experience with side-spill weirs in
England has led to the development of the high
side-spill weir, referred to there as the high double
side-weir overflow. The weirs are made shorter and
higher than would be required for the normal
side-spill weir. The rate of flow to treatment may be
controlled by use of a throttle pipe or a mechanical
gate controlled by a float.
The performance of this type of regulator was
investigated in England (Reference 2). The
experimental structure is shown in Figure 1.12.6. The
structure was sized for a population of roughly 2,000.
Discharge to treatment was 0.94 cfs at first discharge
over weir and this discharge increased to 1.12 cfs
12
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FfGURE 1.72.4
CROSS CONNECTION FOR OVERFLOW,
CONTROL
FIGURE 23
,FLUME INVERT
TO PLANT
PIPE FOR NORMAL FLOW—^
PROFILE ALONG CENTER LINE
OVERFLOW WEIRS
WITH DIP PLATES
CHANNEL FOR NORMAL
FLOW 8 HEAVY SOLIDS
FLUME FOR
FLOATING
MATERIAL
PIPE FOR NORMAL
FLOW 8 SOLIDS
SECTION "A"-"A"
FLUME
CONTROL PIPE FOR
OVERFLOW CHAMBER
TO INTERCEPTOR
CONTROL
PIPE
SECTION "B"-"B"
SPIRAL FLOW (HELICAL)
REGULATOR
Courtesy Institution of Civil' Engineers
13
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FIGURE 1.12.5
8*
SECTION "A"-V
»-»«" END ELEVATION
COMBINED SEWER
SCALl OF FEET
"B"
1:4
"A"
PLANT
TO RIVER
PLAN
n.ii ii-ii
SECTION A-A'
POSSIBLE APPLICATION
STILLING POND REGULATOR
SECTION"B"-"B
Courtesy Institution of CivU Engineers
14
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FIGURE 1.12.6
PLAN
"A
•^
"~~H
n
jt — n • ij
•f 1 H
OVCMFLO* VCI* 1
. lit..; _
•TixJn
ELEVATION
TO RIVER
PLAN
SECTION V-"Att
POSSIBLE APPLICATION
HIGH SIDE- SPILL WEIR
SECTION %"-"A"
.BAFFLES
EIR
SECTION "C"-"C"
SECTIONV-B"
Courtesy Institute of Civil Engineers
15
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when total inflow to the regulator was 7.0 cfs. The
orifice on the pipe to the interceptor was 6 inches
wide by 3 1/2 inches high. The ratio of screenings in
the overflow to screenings in the flow to treatment
was 0.5, the lowest of the four types tested. This
device has the best general performance when
compared to the stilling pond, the vortex and the low
side-overflow weir.
1.12.7 BroadcrestedInflatable Fabric Dams
The broadcrested inflatable fabric dam is a
variably-controlled .gating structure manufactured
from reinforced rubberized fabric. This reinforced
fabric is shaped into a sealed tube, capable of being
pressurized with either water, air or a combination of
air and water. Each inflatable dam is adapted to and
designed to be readily installed and operated on
irregular, flat or curved foundation surfaces without
affecting the inflatable dam's design discharge
characteristics and capabilities. The inflatable dam is
installed in a deflated state and therefore assumes the
shape and contour of the foundation surfaces. Flow
in the combined sewer can be regulated and sewage or
storm flow can be diverted to the interceptor by the
operation of the inflatable dam. Flow through the
interceptor to the treatment plant can also be
controlled by inflatable dams or by some other gating
device if flow control can be regulated.
Overflow can be regulated by simply increasing
the elevation of the inflatable dam by either
automatic, semi-automatic or manually operated
controls. Only when the capacity of the interceptor
has been reached and the level of the admixture of
sewage and storm water reaches the storage capacity
of the combined sewer system will overflow be
allowed to occur. The inflatable dam is a fail-safe
gating structure which will not allow clogging and
jamming during peak storm periods. The inflatable
dam can be controlled so that hydraulic pressure
provided by the upstream water level in the sewer
conduit will activate a positive deflation mechanism,
allowing excess effluent to run off. Then when flows
subside and overflow pressures are reduced, the
inflation control valves open and the inflatable dam
re-inflates until the designed pressure and dam height
is reestablished.
Crest control for inflatable dams used to regulate
flows in a waterway is based on the relative head
between upstream water level and dam inflation
pressure. When water is used as the inflation medium,
an inverted "U" tube siphon pipe installed in the
drain line provides a fail-safe and positive deflation
mechanism. The height of the siphon apex is
adjustable so that flexibility in settings is possible and
deflation can correspond, as desired, to various
upstream water levels and flow rates. An air vent is
connected to the top of the siphon. With the valve
closed, the siphon will prime whenever dam inflation
pressure, as increased by rising upstream water level,
exceeds the siphon height setting, and continuous
complete deflation then takes place. With the apex
valve open, the.siphon acts as a standpipe and dam
deflation will be partial and intermittent, depending
upon the rates at which flows build up and subside.
Positive deflation control is thus assured under high.
flow conditions, whether the air valve is open or
closed. The siphon serves a secondary purpose in
preventing over-inflation during the Ming operations.
As flows subside, overflow pressure reduces, the
inflation float valve opens, and the dam gradually.
re-inflates until ultimately the upstream pool returns
to normal level and the dam is again at nominal
inflated height.
Air-inflated dams operate under the same fail-safe '
principle as water-inflated dams except that
air-actuated instrumentation and controls excite the
deflation cycle system. The decision as to whether to
use water, air, or a combination of air and water as
the best inflation medium for inflatable dams
depends upon operating requirements. The best crest
control is achieved with water inflation. The use of
air, however, usually results in less cost for fabric and
control equipment, especially when
inflation-deflation cycle tune limits must be quite
rapid. In addition, air inflation is dictated whenever a
dam must remain fully operational during freezing
winter conditions.
Figure 1.12.7 is an artist's conception of a
regulator facility utilizing the inflatable fabric dam.
1.12.8 References
All references listed below are from the
Symposium on Storm Sewage Overflows, May 4,
1967, sponsored by the Institution of Civil Engineers.
1., Smisson, B., "Design, Construction and
Performance of Vortex Overflows".
2. Ackers, P. et al., "Storm Overflow
Performance Studies Using Crude Sewage".
3. Prus-Chacinski, T. M. et al., "Secondary
Motion Applied to Storm Sewage Overflows".
4. Oakley, H. R., "Practical Design of Storm
Sewage Overflows".
16
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FIGURE 1.12.7
ARTISTS CONCEPTION - INFLATABLE FABRIC DAM
Courtesy Firestone Coa'ted Fabrics, Co.
17
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SECTION 2
DESIGN GUIDELINES FOR REGULATORS,
THEIR CHAMBERS AND CONTROL FACILITIES
CONTENTS
STATIC REGULATORS
Page
2.1 Manually Operated Gates 21
2.2 Fixed Orifices (Vertical) 29
2.3 Fixed Orifices (Horizontal)
"The Drop Inlet" 30
2.4 Leaping Weirs 35
2.5 Side-Spill Weirs 36
2.6 Internal Self-Priming Siphons 40
DYNAMIC REGULATORS-SEMI-AUTOMATIC
2.7 Float-Operated Gates 41
2.8 Tipping Gates 51
2.9 Cylindrical Gates 62
DYNAMIC REGULATORS-AUTOMATIC
2.10 Cylinder-Operated Gates 62
2.11 Motor-Operated Gates . . : 73
2.12 External Self-Priming Siphons 73
19
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STATIC REGULATORS
2.1 Manually Operated Gates
2.1.1 Description
The regulator may consist of three chambers: (1)
A diversion charnber, (2) orifice chamber, and (3)
tide-gate chamber. The last chamber may be omitted
when a tide gate is not required. A typical regulator is
shown in Figure 2.1.1.
The diversion chamber contains a dam to deflect
the dry weather flow at right angles to the sewer axis
into the orifice chamber. The diversion dam is usually
set at a maximum height of six inches above the
invert of the combined sewer to minimize backwater
effects upstream in the combined sewer during storm
flows. The diversion channel invert is set so that peak
DWF can be diverted without overflowing the dam.
Excess storm flow will pass over the dam into the
flap-gate chamber and continue to the receiving
waters.
The gate is set in the orifice chamber on the
common wall between the two chambers. The
opening is manually adjustable. The minimum
dimension of the opening should be four inches to
reduce clogging tendencies.
The gate'usually consists of a square sluice gate
or circular shear gate. The use of the gate has these
advantages: (1) The size opening can be adjusted, (2)
the gate can be readily opened to clear it of debris;
and (3) the gate can be readily closed to stop all flow
to the orifice chamber when maintenance is required.
A square or rectangular sluice gate is preferable
to a circular one. When a circular gate is partially
closed the opening is crescent shaped. This form of
opening is more subject to clogging than a square or
rectangular opening because material may become
wedged in the acute angles at the ends of the
crescent.
There is some difference of opinion among
designers as to whether the diversion chamber should
be constructed with or without a channel. If the
channel is used the DWF is conveyed into the orifice
with little or no reduction of velocity and there will
be no deposition of material in the diversion chamber
between storms. If the diversion dam is only six
inches above the invert of the combined sewer it will
cause little impediment to large solids or floating
material during storm flows even if the face of the
dam is vertical. Other designers prefer to omit the
channel and provide a flat slope on the face of the
diversion dam so that storm flows will readily sweep
any deposition on the invert up and over the dam.
However, during low DWF the pool upstream of the
dam will act as a stilling basin and cause grit and
solids to accumulate in the diversion chamber. Odors
may then become a problem. Since the purpose of
the regulator is to convey all sanitary flow including
grit and solids to the treatment plant it would appear
that the use of the channel is preferable.
2.1.2 Design Guidelines
A typical layout for this device is shown in
Figure 2.1.1. For design, obtain all pertinent data for
combined sewer at the proposed location of the
regulator including, diameter, invert elevation, slope,
average and peak DWF and peak storm flow. The
regulator design flow is considered herein to be the
peak DWF. Obtain similar data for the interceptor at
the proposed junction with branch interceptor. If the
interceptor is being designed in conjunction with the
regulator assume the elevation for interceptor and
adjust as found necessary by subsequent
computations.
The gate may be either square, rectangular or
circular. The design computations which follow are
based on the use of a rectangular orifice. Discharge
through,the orifice is proportional to the square root
of the head on the orifice. Hence a four-fold increase
in the head will result in a two-fold increase in the
discharge. During low flow periods, discharge will be
determined on the basis of critical depth through the
orifice, providing the water surface downstream of
the orifice is lower. As the depth of flow increases
and rises above the top of the orifice, discharge will
be based on the- difference between the heads on the
two sides of the orifice. The orifice chamber and
branch interceptor must be designed so that there will
be no backwater in the orifice chamber to affect the
discharge from the orifice at design flow. The branch
interceptor should be designed to carry the peak
dry-weather sanitary flow. As the diverted flow
exceeds the peak DWF the hydraulic gradient of the
branch interceptor will increase, thus raising the
water surface in the orifice chamber downstream of
the orifice. The resultant submergence of the orifice
will reduce the head on the orifice and this will
decrease the discharge through it during storm
periods.
Thus, the quantity of storm flow diverted to the
interceptor is affected by two factors: (1) The effect
of the increased depth of flow in the combined sewer
on discharge through the orifice is lessened because
the discharge is proportional to the square root of the
head . on . the orifice; and (2) the increase in
intercepted flow may exceed the capacity at normal
21
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FIGURE 2.1.1
ORIFICE CHAMBER-^
MANUALLY OPERATED GATE
COMBINED SEWER
"A"
DIVERSION CHAMBER
PLAN
0
£
S
K
Z
vJ
1 ^
.: ?l*^>Vyr?1
• ^'
>.;
'••:s
.;i
•*".
• ii
r..'-
* ..
ORIFICE CHAMBER
«=P
^=
i^^'.-v:^^^!
O;
i-_-
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C
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DIVERSION
CHAMBER
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1 PcV,''\"''i;CvV-':'.XJ:-t'*'.''.:-':V-'"-'-v-^
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FLOW
COMBINED
SEWER
,.-.
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1
SECTION "A" - "A"
TYPICAL LAYOUT
MANUALLY OPERATED GATE
22
-------
flow depths of the branch interceptor, thus raising
the hydraulic grade line in the orifice chamber and
reducing the effective head on the orifice. The second
factor becomes more pronounced as the branch
interceptor length is increased. It is, accordingly,
desirable to locate the regulator some distance from
the interceptor—at least 100 feet. Further, to not
cause backwater from the branch interceptor in the
orifice chamber it is desirable that the flow in the
branch be subcritical at design flow.
If field conditions are such that the branch
interceptor cannot be designed to meet the foregoing
criteria it may be necessary to provide some flow
control device in the orifice chamber. This could be a
vertical stop log control, as used for the
cylinder-operated gate, or an orifice either in the
channel or on the outlet pipe from the orifice
chamber.
The hydraulic gradient and energy lines for peak
DWF should be computed starting with the water
surface at the interceptor and proceeding upstream
along the branch interceptor to the orifice chamber.
The elevation of the control dam in the diversion
chamber is usually set 0.5 feet maximum above invert
of the combined sewer. The size of the orifice should
be selected and the required head to pass the design
discharge should be determined. The invert of the
orifice should be set at the required elevation and
water surface downstream of orifice in orifice
chamber should be determined. The water surface
should be compared with required hydraulic grade for
the branch interceptor. Elevations of the latter and
the size of the orifice must be adjusted as required.
The quantity diverted to the interceptor during
storm periods is determined by the trial and error
method.
In the initial computation, the hydraulic
computations should start at the water surface in the
interceptor at peak DWF. In subsequent trials it may
be necessary to raise the branch interceptor at its
junction with the main interceptor which will result
in flow at critical depth at the end of the branch
interceptor. In this case it may be necessary to
compute the backwater curve for the flow in the
branch interceptor to determine the depth of flow at
the upstream end.
Sample computations are given in paragraph
2.1.3 of this manual.
2.1.3 Sample Computation
Manually Operated Gate
Pertinent data
A = Cross Sectional area in sq. ft.
D = Diameter
V = Velocity
d = Depth of flow
Q = Quantity of discharge
b •.= Width of opening
Interceptor
D = 36", Invert el. = 10.0, W.S. = 12.4
Combined Sewer
D = 54 ", Invert el. = 16.00, s = 0.0026
Manning n = 0.013, V (full) = 6.4 fps
Q d
Flow cfs ft.
Hm = Minimum specific energy
HGL= Hydraulic grade line
dc = Critical depth of flow
g = Acceleration of gravity
C = Coefficient
W. S.= Water surface elevation
DWF = Dry-weather flow - av
Dry-weather - peak
1-year storm
10-year storm
0.5
2.0
0.3
0.5
2.5
3.6
V
fps
1.8
2.5
6.7
7.2
(D.
includes peak dry-weather flow
Distance from interceptor to regulator = 100'
HGL = hydraulic grade line
EL = energy line
W.S.
el.
16.5
18.5
19.6
23
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2.1.3 Manually Operated Gate
Design Q = 2.0 cfs
See figure 2.1.3.1
Invert
ELEVATION
HGL
Interceptor - peak dry-weather flow 10.0
Determine lowest profile of branch interceptor
Branch interceptor
L = 100' n = 0.013 Q = 2cfs
D= 10' 8 = 0.008
V (full) = 3.7 fps
d/D = 0.8 V = 1.14 x 3.7 - 4.2 fps
V2/2g = 0.27
Lowest possible invert
12.40 - 0.8 (0.83)
Pipe outlet loss 1.0 (0.27 - 0) = 0.27
Friction head 100 x 0.008 = 0.8
Branch Interceptor
Upstream end
At orifice chamber
Pipe inlet loss 0.5 (.27) = 0.14
Assume complete loss of velocity in orifice
discharge. Water surface in orifice chamber
same as EL.
11.74
12.40
Invert
12.54
12.40
ELEVATION
HGL
13.20
13.61
EL
12.67
EL
13.47
.14
13.61
Diversion Chamber
Dam = 16.00 + 0.50 = 16.50
Try 12" x 12" sluice gate
Determine invert elevation
Q = 3.09 b Hm 3/2
2.0 = 3.09 x 1 x Hm 3/2
Hm =0.75
dc = 2/3 0.75 = 0.50
Vr =Q _2.0 _.
16.50
0.5Vc2
H,
0.75 + 0.5
64.4
d = 0.881
Check - From Fig. 2.1 .3.2 d = 0.881
24
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FIGURE 2.1.3.1
HYDRAULIC PROFILE (I)
MANUALLY OPERATED GATE
25
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FIGURE 2.1.3.2
133d-H
26
-------
2.1.3 Manually Operated Gate
Set invert of orifice at 0.881 below flow line
16.50-0.88 =
ELEVATION
Invert HGL EL
15.62
Orifice Chamber
Orifice
Invert
HGL = 15.62 + dc = 15.62 + 0.50
Assume Velocity head loss
Branch interceptor can be raised
until HGL at upper end is 16.12
Rise = 16.12 - 13.61 = 2.51
15.62
16.12
16.12
Orifice Chamber
Revised branch interceptor—Highest profile
VJ Downstream 11.74 + 2.51
14.25 + (.8) (0.83) - 14.25 + 66
Outlet loss V2/2g = 0.27
Friction loss 100 x 0.008 = 0.80
Upstream end
Pipe inlet loss 0.5 x 0.27 = 0.14
Required water surface
2.J Invert of orifice chamber
Notes:
!•_/ Critical depth will occur at downstream end of
branch interceptor. However computation of
backwater curve indicates normal flow depth
will occur 10 feet upstream from outlet.
Therefore the computations to determine
upstream conditions can ignore critical depth.
2./ This is maximum elevation for invert at chamber
and will result in greatest submergence of orifice
when diverted flows exceed 2.0 cfs. The invert
and branch interceptor can be set lower but
this will decrease submergence of orifice at
higher flows and will result in greater diversions.
ELEVATION
Invert HGL EL
14.25
14.91
15.05 15.71
16.12
15.05
15.18
15.98
16.12
27
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FIGURE 2.1.3.3
HYDRAULIC PROFILE (2)
MANUALLY OPERATED GATE
28
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2.1.3 Manually Operated Gate
Determine flow diverted to branch interceptor in wet
weather periods by trial and error
HGL in combined sewer
Q diverted cfs-assume
V-fps
10" branch S for EL
Top branch lower end J_
Exit loss V2/2g
Friction loss 100 x S
Ent. loss 0.5V2/2g
HGL in orifice chamber
18.38
1-year
storm
18.50
2.9
5.3
0.018
15.08
0.44
1.80
0.22
17.54
Total head (H) on orifice 19.6 - 18.19
Q - 2.81 V FT
Diverted Q cfs
Ratio WWF .= WWF
DWF 0.5
1.22
3.3
3.3
0.96
2.9
2.9
VJ Critical depth is 0.78'. Backwater computation
indicates pipe will be flowing full 2 feet from
end. Assume pipe is flowing full at end.
= CAV~2gH = 0.7 x 1.Ox 0.53 x 8.03V H =2.98^ H
2.2 Fixed Orifices (Vertical)
2.2.1 Description
The regulator is. similar in all respects to the
manually operated gate except that no gate is used.
2.2.2. Design Guidelines
The design guidelines for the vertical orifice are
the same as those established for the manually
operated gate in 2.1. In the description of the latter
device it is stated that if the flow in the branch
interceptor is not subcritical it may be necessary to
install a control in the orifice chamber to cause
submergence of the orifice chamber to cause
submergence of the orifice and thus reduce the
amount intercepted during storm periods. To
accomplish this purpose the Allegheny County
Sanitary Authority has installed a "double-orifice
regulator" which uses a rectangular orifice between
the combined sewer and orifice chamber and a
circular orifice on the outlet from the orifice
•chamber. The branch interceptor is designed with
sufficient slope so that the outlet orifice functions
with free discharge. Sample computations for a single
29
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fixed vertical orifice would be similar to those
presented in 2.1.3 for a manually operated gate.
2.3 Fixed Orifices (Horizontal)
(The Drop Inlet)
2.3.1 Description
When the horizontal orifice is located in the
invert of the combined sewer it may consist of an
open slot or an inlet with a metal grating. After
droping through the slot or grating the flow is
conveyed by the branch interceptor to the
interceptor. A dam is required immediately
downstream of the orifice to prevent overflows
during dry weather periods.
When the horizontal orifice is located in a
separate chamber the regulator consists of a diversion
chamber, orifice chamber and, when necessary, a tide
gate chamber.
The diversion chamber is similar to that used for
manually operated gates. The opening in the common
wall between the diversion chamber and Hie orifice
chamber should be made large enough so as not to act
as a control orifice during dry-weather peak flows.
The invert of the diversion chamber can be provided
with a channel or a flat bottom.
Dry-weather flow in the combined sewer is
diverted by the dam in the diversion chamber into the
orifice chamber through an opening in the common
wall between the diversion and orifice chambers. The
orifice is set horizontally in the bottom of the orifice
chamber at sufficient depth below the diversion dam
to intercept the design flow. The flow passing
through the orifice drops into the branch interceptor
which conveys the flow to the interceptor. The
orifice may be either circular or rectangular. If
circular, provision should be made for replacing the
orifice plate, when necessary, to change the size of
the orifice. If rectangular, the orifice can be made by
using two fixed plates and two removable plates so
that the size of the opening can be revised. Stop
planks should be provided in the diversion chamber
to prevent flow to the orifice chamber when
adjustments are made to the orifice.
2.3.2 Design Guidelines
The area of grate to provide for an orifice located
in the sewer invert can be determined from the orifice
formula, using the head on the grate caused by the
dam. It is difficult to decide what allowance should
be made for clogging. A reasonable assumption is that
50 percent of the grate opening area is available for
flow. Hence, if a storm occurs when the grate is clean
an excessive flow may be intercepted. On the other
hand, the first rush of storm flow may carry so much
debris that the grate becomes clogged very quickly.
For the foregoing reasons it is considered preferable
to place the horizontal orifice in a separate chamber.
During dry weather flow the hydraulic gradient
at the upstream end of the branch interceptor should
be below the orifice for proper functioning of the
regulator. If the hydraulic grade line is just below the
orifice during dry weather flows and the branch
interceptor is designed for subcritical flow, then
storm flows will cause the hydraulic grade line to rise
above the orifice and the flow into the branch
interceptor will be governed by the hydraulics of the
branch interceptor rather than by the orifice. Since
this will reduce the amount intercepted during wet
weather periods it is desirable to make the branch
, interce'ptor of some length, say at least 100 feet, so as
to develop such a backwater effect. It should also be
noted that during storm flows the vertical opening
between the diversion and orifice chambers will act as
an orifice. The height of the opening is usually made
large enough so that the vertical opening will have
little effect on the size of the flow diverted to the
interceptor. The height of this opening could be
decreased to further decrease the diverted flow. This
in effect, would be designing a double orifice
regulator, with one orifice vertical and one
horizontal.
2.3.3 Sample Computation
Horizontal Orifice
d = depth of flow
A = area
C -coefficient
L - length
g = gravity acceleration
Given
Interceptor Sewer
Dia. = 36", Invert el. = 10.0
Water surface = 12.4
30
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2.3.3 Horizontal Orifice
Combined Sewer
Dia. = 54", Invert el. = 16.00, S = 0.0026
Manning n = 0.013
V (full) = 6.4 fps
Flow
Dry-weather-av
Dry-weather-peak
1-year storm
10-year storm
Design Q = 2.0 cfs
See Figure 2.3.3.1
Interceptor
Diversion Chamber
cfs.
0.5
2.0
60.0
100.0
ft.
0.3
0.5
2.5
3.6
V
fps
1.8
2.5
6.7
7.2
WS
el.
16.3
16.5
18.5
19.6
Distance from interceptor to regulator = 100 ft.
HGL = hydraulic grade line
EL = energy line
Design flow in sewer = 16.5 cfs
Damelev = 16.5'
= 0.5' above invert
Side Opening
Say 2.0' wide
Area = 2.0 x 0.5 = 1.0 sq. ft.
V = 2.0 4- 1.0 = 2 fps
Flow toward orifice chamber
90° bend loss V2/2g = 0.06
Orifice Chamber
Assume loss of velocity head
Try 9" x 8" orifice
2.0 = (0.6) (0.5) (8.03) VTT
H = 0.83 ft.
V = 2.0 4- 0.5 = 4 fps
El. orifice = 16.44 -0.83
ELEVATION
Invert HGL EL
10.0 12.4
16.0 16.5 16.5
16.44 16.50
16.44 16.44
15.61
31
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FIGURE 2.3.3.1
HYDRAULIC PROFILE FOR
HORIZONTAL ORIFICE
REGULATOR
32
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2.3.3 Horizontal Orifice
ELEVATION
Invert HGL EL
Branch Interceptor
L = 100' n = 0.013 Q = 2cfs
D = 10", 8 = 0.008 V = 3.7, V2/2g = 0.21
d/D = 0.8, V = 1.13x3.7 = 4.2fps, V2/2g = 0.27
Downstream End
12.40 - (0.8 x .83) = 12.40 - 0.66
Exit loss V2/2g = 0.27
Upstream End
Friction loss 100 x 0.008 = 0.80
Bend loss 0.25 V2/2g 0.07
Distance of HGL below orifice
15.61 - 13.27 = 2.34
12.40
11.74
12.54
13.20
13.27
12.61
13.47
13.54
Use 10" C.I. ASA 21.10 90° bend
Highest invert = 15.61 - 1.67
From above inv. = 13.27 - 0.66
Raise branch interceptor
13.94
12.61
1.33
Note: Flow at critical depth will occur at downstream end.
Flow at normal depth will occur 10' upstream.
Therefore, computation of upstream condition can ignore critical depth at lower end.
Revise elevations of
Branch Interceptor
Downstream end
11.74+1.33
Upstream end
90° bend loss
Below orifice
ELEVATION
Invert HGL EL
13.07
0.80
13.87
13.73
0.80
14.53
0.07
14.87
14.00
0.80
14.80
0.07
14.87
Determine flow diverted in wet weather
33
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FIGURE 2.3.3.2
HYDRAULIC PROFILE
HORIZONTAL ORIFICE
REGULATOR
34
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2.3.3 Horizontal Orifice
Figure 2.3.3.2 Estimated
Q cfs
10" S =
V =
Top of sewer downstream
Exit loss
Friction loss
Bend loss
Subtotal
HGL above horizontal
Orifice V
Entrance loss 0.5 V2 /2g
Enlargement loss
HGL in orifice chamber
HGL in diversion chamber
2.0' x 1.5 opening
V = Q* (0.7) (3) (8.03); H
HGL in Orifice Chamber
Difference in HGL
Ratio WWF: DWF = WWF/0.5
10-year storm
4.3
0.039
7.9
13.90
0.97
3.90
0.24
19.01
Yes
(8.6)
0.58
0.02
19.61
19.60
0.07
19.53
0.08
Close enough
8.6
1-year storm
3.9
0.032
7.2
13.90
0.81
3.20
0.20
18.11
Yes
(7.8)
0.47
0.01
18.59
18.50
0.05
18.45
0.14
Close enough
7.8
2.4 Leaping Wiers
2.4.1 Description
Leaping weirs are of two types: (1) continuous
invert type; and (2) stepped invert type.
The" continuous invert type has no drop in the
invert at the horizontal orifice in the bottom of the
sewer to change the elevation of the invert. The
stepped invert type has the upstream invert raised
above the downstream invert. Since regulators usually
are constructed on existing combined sewers in which
no drop has been provided, this requires that a plate
with a raised lip be installed on the upstream side of
the opening..
Some designs provide for the installation of
adjustable plates to modify the size of. the opening
and thus the amount of intercepted flow. However,
considering the effect of bridging and clogging of the
weir with debris, the necessity of making such close
adjustments is questionable. It is also doubtful
whether such adjustments are ever made after
completion, due to the difficulty of operating nuts or
bolts in a constant stream of sewage.
2.4.2. Design Guidelines
There are no generally accepted design criteria
for a leaping weir. Several design methods are given in
standard text books and designers are referred to
these for further information.
35
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2.5 Side-Spill Weirs
2.5.7 Description
The small regulator shown on Figure 2.5.1
illustrates how a side-spill weir can be constructed in
an existing manhole. In the case shown, the designer
also has added a manually operated gate at the outlet
to the interceptor to further regulate the diverted
flow. It should be noted that too great a restriction
on the outlet may make the side:spill weir formula
inapplicable.
FIGURE 2.5.1.1
SIDE - OVERFLOW WEIR
FOR SMALL OVERFLOW
DAM
"A" 4
PLAN
SECTIONAL PLAN
STANDARD MANHOLE
FRAME AND COVER
BRICK
SECTION "A"-'A"
SECTION "B"-"B'
Courtesy Institution for Civil Engineering
Studies recently have been carried out on the
performance of side-spill weirs in England. (Ackers,
P., et al., "Storm Overflow Performance Studies
Using Crude Sewage.") The first spill occurred at an
inflow of 0.54 cfs compared with the design figure of
0.90 cfs. The maximum flow of 0.54 cfs compared
with the design figure of 0.90 cfs. The maximum flow
to treatment was 1.4 cfs when the total inflow was
6.5 cfs. When the orifice was removed from the outlet
pipe the flow to the interceptor was 2.6 cfs when the
total flow was 8.2 cfs. The report states: "Attempts
to calculate the discharges for this overflow from
classic side-weir theory failed to give satisfactory
agreement with observed values." It further states:
"The poor degree of control achieved with the low
side-weir overflow confirmed previous opinion. It
spilled prematurely, as well as failing to limit flows to
the desirable maximum."
A possible application of the side-spill weir using
a double weir is shown in Figure 1.12.6
2.5.2 Design Guidelines
Various formulas have been presented in the past
for the design of side-spiE weirs. However, they have
failed to be accepted and little or no data on actual
performance in the field have been presented to
confirm their validity. Two methods are described
herein which appear to offer more reliability than
previous formulas.
The characteristics of flow over side-spill weirs
are related to the type of flow in the main channel.
The work of investigators who dealt with this
problem indicates that when the depth of flow in the
main channel or pipe is at or below critical depth,
with the wier height lower than critical depth or
when the flow depth is greater than critical in a steep
slope channel and the weir height is above critical
depth, the surface curve of flow over the side-spill
weir will be lower downstream. When the channel or
pipe flow is 'at a depth greater than critical depth in a
channel on a flat slope and the height of the weir
crest is greater than critical depth, the surface curve
over the side-spill wier will be lower at the upstream
end but will rise downstream. For purposes of
hydraulic analysis the assumption is made that the
specific energy line Ho referred to the channel invert
remains horizontal for the length of the side-spill
weir. The error due to this assumption is generally
within acceptable limits.
a. Determination of Weir Discharge
by Use of Q Curve
A method for determination of side-spill weir
flow proposed by de Marchi5 utilizes the concept of
the Q curve which is a-graphical representation of the
changes that occur in a flowing stream or channel of
constant cross section of flow for a fixed value of the
energy level Ho.
The specific energy (referred to low point of
cross section, i.e. invert of channel) is generally
expressed as:
Energia Elettric, July, 1941
36
-------
H0=d + Q2/(A2x2g)
H0 = Energy line level
d = Depth of flow
Q = Quantity flowing
A = Area of flow
Assume the Ho value to be fixed, then
Q = A[2g(H0-d)] % = 8.02A [Ho-d] &
To construct the Q curve, let d vary from zero to
H0 and for each increment compute value of Q. Plot
computed values of Q on horizontal axis vs.
corresponding value of d on vertical axis. For a given
fixed H0 the maximum value Q will be at
dc=(H0-dm)^ where dm is the mean depth. Tor a
rectangular section dc=2/3 Ho; for a triangular
section dc=4/5 Ho; similarly for other cross sections.
The value of dc is the critical depth. For a given
energy level Ho, the maximum discharge will be at a
depth dc if the Q flowing is the necessary quantity to
support that flow depth.
The following is based in part on. a presentation
by Prof. K. Woycicki in his book "Kanalizacke",
published in 1955.
In the case of channels in which flows upstream
of the side weir are at depths greater than "dc", the
determinations of diversion over the weir are started
from the downstream end of the side weir. In cases
where the flow depth upstream of the side weir is
lower than "dc", the determinations should begin
from the upstream end of the weir. The Q curve is
drawn from the. channel section immediately
upstream of the side-weir. The length of weir is
estimated for the first calculation and then adjusted
by trial. Generally, known formulas may be used for
first trial. A side-spill weir flow formula adjusted by a
safety factor may be utilized for trial purposes.
Q = 2.01hm3/2(cfs)
(hm = Mean value of head on weir)
For computation purposes fhe side weir is divided
into an equal number of parts—L t, L2, L3, etc. The
above weir formula is also used for calculation of the
partial flows. Horizontal lines are drawn to the Q
curve to represent the level of the side-spill weir and
the maximum flow elevation in the channel upstream
or downstream as the case may be. The flow elevation
downstream is determined in relation to the desired
maximum flow to be delivered to treatment facilities,
employing usual procedures. In the case of an
upstream flow depth greater, than critical,
computations begin at the downstream end of the
side-spill weir. The downstream water surface
elevation, as above determined, minus the elevation
of the weir crest, gives the weir head hx from which
the partial flow is calculated; Subtracting the first
partial discharge from Q on the Q curve establishes
the next water surface level which,, in turn,
determines h2 on Section 12 Again Q2 is computed
and the procedure repeated until the entire water
surface curve for the side-spill weir is established. As a
check, the summation of partial Q's should equal Qt
Q2 the desired diversion quantity. In the case of an
upstream flow depth less than critical, the procedure
of calculation is similar except that computations
begin at the upstream end. In the event -of lack of
agreement, the side-spill weir length must be
modified, lengthened or shortened, and calculations
repeated until agreement with Ch - Q2 is obtained.
The above-described method entails, of necessity,
a cut-and-try procedure because of the unknown
varying head conditions on parts of the side-spill weir.
The theoretical considerations of the de Marchi
method are predicated on the following:
1. Steady flow conditions exist;
2. Weir is in a long channel of uniform
cross-sections;
3. Crest of the weir is parallel to the bed of the
channel;
4. Uniform flow exists upstream and
downstream of the weir;
5. Energy line is parallel to the bed of the
channel; and
6. Discharge over weir may be computed by a
weir-type expression.
Alternative Method for Design
of Side-Spill Weirs
A more direct determination of weir length was
developed by Mr. Peter Ackers in a paper published in
the Proceedings of the Institution of Civil Engineers
in 1957, titled "A Theoretical Consideration of Side
Weirs on Storm Water Overflows."
The formulas developed by Ackers apply only to
a falling profile and only when the weir height is less
than half the height of the energy line relative to the
channel bottom. If these conditions are satisfied the
formulas presented by . Mr. Ackers offer a ..rapid
approach to the determination of required length for
the side weir. This method is inapplicable with a
relatively high side weir. The insertion of dip-plates
(scum baffles) may greatly reduce the discharge if the
clearances are small and formulas for this condition
are also developed in the paper. Further this method
does not take account of downstream control. Where
a controlled outlet exists the method should be
applied with discrimination and only where
conditions are such that a falling profile would
otherwise occur, i.e., c/E^/ is less than 1. The paper
also discusses the effect of a tapered channel on the
method and states that a fate of taper in excess of the
ratio of the overflow per unit length to the channel
37
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the weir is set relatively low.
The paper develops a general differential
equation for the water profile along a side weir and
by substitution of certain factors derives formulas for
the length of weir based on a selected ratio of
upstream head on the weir to downstream head on
weir. The theoretical profile is shown in Figure 2.5.2.
The formulas are as follows:
Ratio n Formula for L
5 L = 2.03B(2.81 -1.55
7 L = 2.03B (3.90 - 2.03
10 L = 2.03B (5.28 - 2.63
15 L = 2.03B (7.23 - 3.45
20 L = 2.03B (8.87 - 4.13
Notes to above: Add 10% for broad-crested weir.
Halve length for double-sided weir.
The notation used is as follows:
L = length of weir
hi = upstream head on weir
h2 = downstream head on weir
n = hi /h2
c = height of weir crest above invert
B = width of channel or dia. of pipe
E = specific energy related to invert
EW = specific energy related to weir crest
a (alpha) = velocity correction coefficient
P (beta) = pressure correction coefficient.
Upstream of the weir a is 1.2 and |3 is unity.
Along weir a is 1.4 and 0 is 0.8
The original paper gave the following formula for
computing total head based on flow upstream of the
weir.
EW = 1.2 V2/2g + (dn-c) (Equation 1)
However, in discussion published subsequently
Ackers stated the use of this equation "could lead to
anomalies." Therefore, he suggests computing the
head at the upstream end of weir based on the
assumption that hi = % EW which results in
following:
EW = aQ2/2gA21 + %/JEjy (Equation 2)
If the area of the water in a rectangular channel,
i.e. B (c + & Ew) is substituted for AI equation 2
becomes:
[Vel x fl + (Ew/2c)]2 = a/(2-/3) x Q2/(gB2C3)
(Equation 3)
Figure 2.5.3 b was developed to solve this
equation for c/E^, for rectangular channels.
For circular sections the procedure might be the
use of equation 1 for a preliminary value of EW and
then the use of equation 2 by trial and error for a
more exact value.
Having determined C/EW and having selected the
ratio of n, the required length of weir can be
determined by use of Figure 2.5.2, or by the
equations given previously:
Example by Ackers Method:
A combined sewer 48 inches in diameter
constructed on a slope of 0.002, with Manning n of
0.013 has a capacity of 65 cfs flowing full. The
average dry-weather flow is 6.5 cfs. It is desired to
divert flows in excess of 2 x DWF
Upstream flow = 65 cfs
Upstream sewer = 48 in. dia.
Flow to be diverted = 52 cfs
dc = critical depth
dn = normal depth
D = diameter
Q"= sewer capacity
q = design flow
(1) Critical flow depth in 48-inch-diameter pipe
vs. maximum flow depth: From Figure 26,
ASCE manual No. 37
dc/D = 0.60, dc = 0.60 x 4.0 = 2.4 feet
dn = 0.8 x 4.0 - 3.2 feet
Since dn is greater than dc, drawdown will occur
at side weir.
(2) Determine c
forQ = 2xDWF=13cfs
q/Q= 13/65 = 0.20
d/D = O.SO, d = 0.30 x 4.0 = 1 .20 feet
therefore c = 1 .20
Weir crest must be set 1.20 feet above invert so
that 2 x DWF can continue directly downstream.
(3) Determine c/Ew
Assume Figure 2.5.3 B is applicable for circular
channels.
From Figure 2.5.2 B cJE^ = 0.60
Since C/EW is less than 1.0 a falling profile will
develop.
(4) Determine L
Use n = 5 and C/EW = 0.60
From Figure 2.5.2 c L/B = 3.9
L = 3.9x4.0 =15.6 feet or
7.8 feet per side if double weir is used.
(5) Determine hi andh2
c/Ew = 0.60
EW = 1.20/0.60 = 2.00 = 1.00 feet
(double weir)
hi = 0.5 EW =1.00 feet
h2 = 1.00/5 = 0.20 feet
(6) Determine flow to plant
d = c + h2 = 1.20 + 0.20 = 1.40
d/D =1.40/4.00 = 0.35
q/Q = 0.26 (from chart of hydraulic
properties)
q = 0.26 x 65 = 17 cfs which is greater
than 13 cfs desired
38
-------
FIGURE 2.5.2
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LOM«ITUOm»L MCTIOM
CALCULATION OF
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A. THEORETICAL PROFILE
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C. DESIGN CHART
ACKERS METHOD
FACTORS FOR
SIDE SPILL WEI R
.3 456 8 IO 15 2O SO 40 50
RATIO OF .Hi TO H2 - N
Courtesy Institution for Civil Engineers
39
-------
(7) Determine flow to plant for n = 10
If n = 10 were selected then
L = 7.5x4.0 = 30 feet
h2 = 1.00/10 = 0.10 feet and
q=15cfs
2.6 Internal Self-Priming Siphons
2.6.1 Description
Self priming siphons may be classified into two
types: (1) Internal self-priming where the siphon
action is induced by flow in the siphon, and (2)
external self-priming where the siphon action is
induced by flow in a priming tube situated outside
the siphon. An internal type is shown in Figure 2.6.1.
The following discussion relates to internal
self-priming siphons.
The internal self-priming siphon consists of: (1)
Entrance section; (2) upflow leg; (3) vertical throat
section; (4) downflow leg; and (5) outlet section. The
downflow leg is designed with an adverse slope to aid
in creating a negative pressure at the summit. As the
water level rises to the crest of the siphon the water
flows over the crest in a sheet and strikes the opposite
wall of the downflow leg thus sealing the siphon. As
the sheet falls it carries air from the summit with it.
When the upstream water level rises enough to seal
the air vent the falling sheet of water carries out the
remaining air in the summit and the siphon discharges
at full capacity. The siphon continues to discharge
until the upstream water surface falls below the air
vent and enough air is admitted to the siphon summit
to stop the siphonic action. For quick priming action
it is advisable to provide a water seal at the siphon
outlet.
2.6.2Design Guidelines
The use of this type of siphon is considered
herein for discharging excess storm flows to the
receiving waters.
The energy equation for flow through a siphon
is:
H = Vs/2g + K Vs/2g + f (1 + V2)/(D + 2g)
where H = difference in elevation of upstream
and downstream water surface in feet
FIGURE 2.6.1
DOWNSTR EAM
THROAT
CREST
DOWNFLOW LEG
UPFLOW LEG
UPSTREAM
VENT PIPE
WATER SURFACE
SEALING BASIN
INTERNAL SELF-PRIMING SIPHON
40
-------
v = velocity in fps
f = friction coefficient
1 = length of siphon in feet
D = diameter of siphon in feet
K = loss coefficients for entrance, transition,
bend and exit losses.
Due to the difficulty in determining the proper
loss coefficients in the above equation the following
equation also has been used:
Q = CA(2gH)^ where
Q = discharge in cfs
C = coefficient
A = area of throat in sq. ft.
H = same as above in ft.
The value of C. may vary from 0.3 to 1.0 but
generally will range from 0.5 to 0.85 in a
weE-designed siphon.
• Design criteria for siphon and values of the
various loss coefficients are given in paragraph 207 of
"Design of Small Dams, Bureau of Reclamation, First
Edition I960." Figure 237 of that publication is a
chart for determining the value of C for use in an
equation similar to the one given above.
Due to the uncertainty in selecting the proper C
value, some engineers in the past have recommended
this be determined by model test of proposed
siphons.
On a recent project in England, in 1958, siphons
were made of sheet copper and tested before
installation. The copper siphons were then encased in
concrete during construction.
The following, criteria are based on' British
experience:
1. ' The air vent pipe should have a minimum
area of six percent of the throat area.
2. A sealing basin at the outlet is necessary for
efficient priming.
3. A two-inch depth of flow over the crest at
the summit is the maximum necessary to prime
the siphon.
DYNAMIC REGULATORS - SEMI-AUTOMATIC
2.7 Float Operated Gates
2.7.1 Description
This regulator may consist of three chambers: (1)
Diversion chamber; (2) regulator chamber; and (3)
tide gate chamber, when required (Figure 2.7.1).
The diversion chamber contains a dam to deflect
the dry-weather flow into the regulator chamber. In
flat regions, the diversion dam usually is set a
maximum height of six inches above the invert of the"
combined sewer to minimize backwater effects
upstream in the combined sewer during storm flows.
The diversion channel invert is established so that
peak dry-weather flow can be diverted without
flowing over the dam. Excess storm flow will pass
over the dam into the tide gate chamber and to
overflow.
The regulator chamber contains the float, the
regulating gate and . the interconnecting Jinkage
between the float and the gate. The gate is installed
on an opening in the common wall between the
regulator and diversion chambers. Usually the float is
situated in a well which is connected by a telltale
passage to the channel of the combined sewer in the
diversion chamber, or to the channel of the
intercepted flow in the regulator chamber.
There are three principal methods of controlling
the regulating gate. These are designated herein as
Types A, B, and C. In the Type A control the telltale
passage extends from the float well to the combined
sewer and thus reflects the water level in the
combined sewer. This method is used if it is desired
to prevent any diversion of flow to the interceptor
.when the water surface in the combined sewer
reaches a certain level. .
In the Type B control the telltale passage extends
from the float well to the flow channel in the
regulator chamber. This type of control.is used if it is
desired to divert a certain quantity to the branch
interceptor before reducing the amount diverted from
the combined sewer.
The Type C control is similar to Type B except
that an orifice plate is installed in the flow channel
downstream frojn the entrance of the telltale to the
channel. This type of control is used if it is desired to
pass a predetermined quantity through the regulator
regardless of conditions in either the combined sewer
or the interceptor. This type of control generally can
be designed so that the desired discharge can be
controlled within plus or minus 5 to 10 percent. Type
C control is considered the most desirable and is used
herein for illustrative purposes. A typical layout of a
regulator using the Type C control is shown on Figure
2-7.1.
2.7.2 Design Guidelines and Formulas
Type C Control
For design, obtain all pertinent data for the.
combined sewer at the proposed location of the
regulator including diameter, invert elevation, slope,
average and peak dry weather flow and peak storm
flow. Similar data must be obtained for the
Interceptor at the proposed junction with the branch
interceptor. If the interceptor is being designed in
41
-------
FIGURE 2.7.1
"A"
j|
REGULATOR CHAMBER
BRANCH
INTERCEPTOR
««,,-,..=.
ORIFICE
ELl-™LE
FLOAT IN WELL — ^i
n
OVERFLOW
TIDE GATE CHAMBEF
~~
TIDE GATE^^-
DIVERSION
DAM
4,
FLOAT- OPERATED GATE
COMBINED SEWER
CHANNEL
•">• ••«'••; v.-.'v"'';-"^'^".:-:.' :-::..--v.v:/.-. v1 ;•;;?<•;-"•:: .••••>.•.•:.-'
DIVERSION CHAMBER
PLAN
IE
o
l-
Q.
Ill
O
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111
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REGULATOR
CHAMBER
Q
ORIFICE
DIVERSION
CHAMBER
GATE
p
! COMBINED
SEWER
SECTION "A"-lA
"""
TYPICAL LAYOUT
FLOAT-OPERATED GATE
42
-------
conjunction with the regulator, assume the elevation
for the interceptor and adjust as necessary by
subsequent computations.
First, set the limits on the maximum flow to be
diverted to the interceptor.' Usually the object is to
divert the peak dry-weather flow to the interceptor
and hence this value is selected as the maximum
dry-weather discharge through the regulator. This
represents the maximum discharge with the gate fully
open and only dry-weather flow in the combined
sewer. Then the maximum discharge through the
regulator in wet weather will be the peak dry-weather
flow plus a minimum amount varying 10 to 20
percent of the peak dry-weather flow—the maximum
discharge through the partially closed gate with storm
flow in the combined sewer. This minimum variation
between the maximum dry-weather diversion and the
maximum wet-weather diversion is necessary to
provide adequate variation in the water surface in the
float well to cause sufficient float travel as explained
hereafter.
For dry weather conditions the total available
head loss is divided between h ft., the head loss
through the gate and H ft., the head loss through the
orifice. Likewise, under maximum storm conditions
the total available head is split between h inches, the
head loss through the gate and H inches, the head loss
through the orifice. The difference in the water
surface upstream of the orifice under dry-weather and
storm conditions determines the float travel. The
difference in the water surface in the combined sewer
under dry-weather and storm conditions determines
the amount the gate must close, or the shutter travel.
If the ratio of shutter travel to float travel exceeds 2
then: (1) A new head loss must be chosen for the
orifice; or (2) the discharge through the regulating
gate during storms must be increased.
Computations may be made in the following
steps:
1. Design branch interceptor for peak
dry-weather flow.
2. Using peak dry-weather flow, determine
hydraulic gradient at the exit of the regulator
chamber on the following basis:
a. Determine the water surface in the
interceptor. If a drop manhole is required at
the interceptor so that flow at critical depth
occurs, then investigate to see if the branch
interceptor is long enough for the backwater
curve to attain normal depth at the upstream
end of the branch interceptor. Compute the
hydraulic profile upstream to the regulator
chamber.
b. Determine the water surface in the
regulator chamber. Select channel width.
Determine critical depth. Make flow depth
15 percent ox more greater than the critical
depth. Determine the energy line, hydraulic
grade line and invert.
3. Determine total available head between the
hydraulic grade line at the exit of the regulator
and the dam elevation in the combined sewer. To
minimize backwater effect in the combined sewer
during storm flows, it may be advisable to set the
dam a maximum of six inches above the invert of
the combined sewer.
4. Using about one-half of the total available
head as H ft., determine the orifice area.
Use Q = CA (2gH2)^ with C = 0.70.
5. Determine the hydraulic grade line
immediately downstream of the orifice. Use ds =
d? [l+(2V22/gd2) x (l-da/di)]^ (King 5th,
Equation 4-25)
Where ds = depth of flow
downstream of orifice
d2 = depth of flow downstream below
turbulence
V2 = velocity at d2
dj = height of orifice
Q = quantity
A = area
C = coefficient
6. Determine the total available head on the
basis of d2 above.
7. Determine h ft. (head loss through gate).
8. Select regulating gate.
Use Q = CA (2gHP with C = 0.95 to obtain
required area. Select the nearest regulating gate
size. On the basis of the size selected, determine
h ft. (Head loss through gate.)
9. Check orifice size. Determine new H ft. on
the basis of h ft. determined in Step 8. Repeat
computation for total available head and orifice
size until the error is minor.
10. Establish regulator gate elevations so that the
gate is submerged on the downstream side with
peak dry-weather flow.
Using the maximum wet-weather diverted flow,
proceed as follows:
11. Determine the hydraulic grade line at the
regulator chamber exit. Proceed upstream from
the upstream end of branch interceptor, selecting
trial depths and comparing the energy line in the
channel with the sum of the energy line in the
branch interceptor and entrance loss.
12. Determine H in., the head loss through the
orifice. Use Q = CA (2gH)^ with C = 0.7.
13. Check the hydraulic grade line downstream
43
-------
of the orifice, using equation in Step 5.
14. Determine the hydraulic grade line upstream
of the orifice.
15. Determine the float travel (F.T.) as the
difference in the hydraulic grade line upstream of
orifice for peak dry-weather flow and the
maximum storm diverted flow.
16. Determine shutter travel (S.T.), the amount
the shutter of the gate must close so that the
discharge during storm flow will not exceed the
maximum diverted flow. It is necessary to use
manufacturer's charts for this computation since
the coefficient of discharge for the .gate varies
with the closing of the gate.
17. Determine ratio of S.T. to F.T. If this ratio is
less than 2, design is satisfactory. If ratio is
greater than two, then redesign must be made, as
stated above.
Sample computations follow. The hydraulic
profiles for these computations are shown in Figure
2.7.3.
In the design computations friction head losses in
the channels are neglected since these losses are
minor. It is also assumed that there is complete loss
of velocity head of the flow entering the diversion
chamber and of the flow entering the regulator
chamber. A 90-degree bend in the channel of the
regulator chamber is considered advisable to eliminate
the latter velocity head so that the orifice design may
disregard the effect of approach velocity.
2.7.3 Sample Computation
Float-Operated Gate
Pertinent data
Interceptor sewer
D = 60", Invert el. = 10.0 ft., W.S. = 14.0 ft. for 34.2 cfs diversion
and 13.77 ft. for 30 cfs diversion
Combined sewer
D = 60", Invert el. = 17.0 ft., S = 0.0022
Manning n = 0.013, V (full) = 6.2 fps
DWF = Av. dry-weather
Peak dry-weather
Peak storm
cfs
15
30
120
d
ft.
1.20
1.70
4.00
W.S.
El.
18.20
18.70
21.00
V
fps
4.3
5.2
7.0
Distance from interceptor to regulator on combined sewer is 100 ft.
HGL = hydraulic grade line
EL = energy line
Use Brown & Brown Regulator with Type C Control. Maximum diversion will exceed design
diversion by 10 to 20%. Use 14%.
h' = head loss thru regulator gate during dry-weather flow
44
-------
FIGURE 2.7.3
«*• O _|
» I O
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os!-g
i ir °
O !|! O
h. « Ul
^
= 3 «
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111 111
a. a u
o o J
ui u ^
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< CD
HYDRAULIC PROFILES FLOAT-OPERATED GATE
45
-------
2.7.3 Float-Operated Gate
h" = head loss thru regulator gate during storm flow
H' = head loss thru orifice during dry-weather flow
H" = head loss thru orifice during storm flow
d = depth of flow
D = diameter
dc = critical depth
Regulator should pass peak dry-weather flow
Design diversion = Q = 30 cfs
Maximum diversion = Q'
Q+ 14% - (30) (1.14) = 34.2 cfs = Q'
Interceptor
Branch Interceptor Use n = 0.013
Determine hydraulic profile
Q' = 34.2 cfs
Use D = 30 in., S = 0.007
V (full) = 7.1 fps
V = 1.13 x 7.1 = 8.0 fps @ 2' flow depth
V2/2g=1.00
d = 0.8 x 2.5 = 2.0
downstream end
Rise = 100x0.007 = 0.70
upstream end
ELEVATION
Invert HGL EL
10.00 14.00
13.77
12.00 14.00 15.00
12.70 14.70 15.70
Q = 30.0 cfs
Q/Q1 =0.88
d = 0.71x2.5 = 1.77 ft.
V = 1.12x7.1 =8.0
46
-------
2.7.3 Float-Operated Gate
V2/2g = 1.00
downstream end
Rise = 0.70
upstream end
Regulator Chamber Q = 30 cfs
Use channel width = 2.5 ft.
dc = 1.62 (Fig. 37 ASCE Manual 37)
For stable flow d - 1.5 x 1.61 = 1.86
Determine d at chamber exit by trial for energy balance
d = 2.9ft. HGL = 12.70+ 2.9
V = 30 -5- (2.9) (2.5) = 4.13 fps
V2 /2g = 0.26 EL = 15.60 + 0.26
Entrance loss = 0.5 (1 — 0.26) = 0.37
EL - 15.47 + 0.37 = 15.84 < 15.86
Check OK
Neglect friction head loss in channel
Determine total head
Diversion dam = 17.00 + 0.50 = 17.50
W.S. regulator 15.60
Total head-1st trial 1.90
Trial H'= 1.90 + 2 = 0.95
Determine orifice size
ELEVATION
Invert HGL EL
12.00 13.77 14.77
12.70 14.47 15.47
12.70 15.60
15.86
30 = (0.70) A (8.03) V 0.95
A = 5.48
Try orifice = 2.5 ft. wide by 2.19 ft. high
47
-------
2.7.3 Float-Operated Gate
Determine HGL downstream of orifice
ds = d2 [ 1+2VJ (1 -dz) ]1/
(from King 5th, equation 4—25)
ELEVATION
Invert HGL EL
= 2.9 [ 1 + (2) (4.13)2 (1 - 2.9)
(32.2) (2.9)
2.19
^2.72
HGL = 12.70+ 2.72 = 15.42
Determine total head
Diversion dam = 17.50
HGL downstream orifice 15.42
Total head - 2nd Trial 2.08
12.70
15.42
Trial
Determine regulating gate size
Trial h' = total head - H'
= 2.08-0.95 = 1.13
Q =CAV2gH
30 = (0.95) (A) (8.03) V 1.13 , A = 3.70 sq. ft.
From Brown & Brown Catalog
Use Gate No. 7 A = 3.81
16 in. high x341A" wide
Determine h' based on Gate No. 7
30 = (0.95) (3.81) (8.03) Vli7"
Final h' =1.06
Re-determine orifice size
H' =2.08-1.06 = 1.02 ft.
30 =(0.7) (A) (8.03) V 1.02
A = 5.30 sq. ft.
Orifice = 2.5ft. wide x 2.12 ft. high
Re-check Total head
Ds = 2.70
HGL downstream orifice = 15.40
Diversion dam = 17.50
Final total head = 2.10
12.70
15.40
Final
48
_
-------
2.7.3 Float-Operated Gate
Re-determine orifice size
Final H'= 2.10 - 1.06 = 1.04
A =5.25 sq.ft.
Orifice = 2.5 ft. wide
2.1 ft. high
Upstream of orifice
HGL = 15.40+H'
= 15.40+1.04
Regulator Chamber
Determine setting of regulating gate
Submerge by 0.11 ft.
Top = 16.44 - 0.11 = 16.33
Invert =16.33 - 1.33 = 15.00
Determine conditions for Q' = 34.2 cfs
Head loss at orifice = H"
Q' = CAV2gH
34.2 = (0.7) (5.25) (8.03) V H"
H" =1.35 ft.
Upstream end of branch interceptor
Determine d at chamber exit by trial
for energy balance
d = 3.0 + HGL = 12.70 + 3.0
V = 34.2 4- (3.0) (2.5) = 4.56
V2 729 = 0.32 EL - 15.70 + 0.32
ELEVATION
Invert HGL EL
12.70 16.44 16.44
12.70 14.70 15.70
12.70 15.70
16.02
Entrance loss = 0.5 (1.00 - 0.32) = 0.32
EL = 15.70 + 0.34 = 16.04> 16.02
Check OK
Check HGL downstream of orifice
ds = d2 [ 1 + 2v| ( 1 - d2
gd2 dt
= 3.0 [ 1 + (2) (4.56)2 (1-3.0) ]1/2
.(32.2){3.0) 2.1
= 2.70
49
-------
2.7.3 Float-Operated Gate
ELEVATION
Invert HGL EL
HGL « 12.70 + 2.70 = 15.40
HGL upstream of orifice
HGL = 15.40+H"
= 15.40+1.35
15.40
16.75
Regulator Chamber
Float travel = F.T.
HGL for 34.2 cfs= 16.75
HGL for 30.0 cfs = 16.44
F.T. = 0.31
h" - 21.00 - 16.75 = 4.25 ft.
From Brown & Brown Catalog
C = coefficient of discharge
P = % of gate opening
CP =Q' =34.2
2gh" (3.81) (8.03) V 4.25
= 0.54
From chart D.S. 347, Brown & Brown
For CP = 0.54
C = 0.79
and P = 68.5%
Height of gate opening = .685 x 1.33
= 0.91 ft.
S.T. = gate shutter travel
S.T. = 1.33 - 0.91 - 0.42 ft.
S.T. = 0.42 = 1.35 < _2_
F.T. 0.31 1 1
50
-------
2.8 Tipping Gates
2.8.1-Description
The regulator structure is similar to that required
for manually operated gates. A typical regulator with
tipping gate and flap gate is shown in Figure 2.8.1.1.
The detail of the tipping gate as used in
Milwaukee about 1919 is shown in Figure 2.8.1.2.
The horizontal pivot is located so that one-third of
the plate is below the pivot. The housing for the gate
is precast concrete and was made with opening widths
of 12, 18, and 24 inches.
The detail of the gate as used recently is shown in
Figure 2.8.T.3. This gate is made in opening widths of
8, 12, 24, and 36 inches. Where an opening wider
than 36 inches is required, multiple gates are used.
This model of tipping gate is used by the Allegheny
County Sanitary Authority, Pittsburgh, Pa. The gate
differs from the gate used in Milwaukee in that: (1)
The housing is of cast metal rather than concrete; (2)
the bottom third of the plate below the pivot has a
deflection angle of about 24 degrees with the upper
part of the plate; (3) the top of the housing is curved
to provide minimum clearance between the housing
and the top of the plate as the latter rotates; (4) the
maximum and minimum opening can be adjusted;
and (5) the bottom is fixed rather than adjustable.
2.8.2 Design Guidelines
For design, obtain all pertinent data for the
combined sewer at the proposed location of the
regulator, including diameter, invert elevations, slope,
average and peak dry-weather flow and peak
wet-weather flow. The design flow is considered
herein to be the peak dry-weather flow. Similar data
for the interceptor at the proposed junction with the
collector are required.
Compute the hydraulic grade and energy lines for
peak dry-weather flow, starting at the interceptor and
proceeding upstream along the branch interceptor to
the tipping gate chamber. Determine the elevation of
the diversion dam in the diversion chamber.
Determine the differential head available and select
the size of gate and gate opening from Figure 2.8.2. If
the available differential head is greater than that
required for the design flow, the head can be
decreased by raising the branch interceptor .and
raising the water .surface downstream of the gate.
Since the data for Fig. 2.8.2 are based on a minimum
downstream water depth of 10 inches, the tipping
gate should be set with its invert 10 inches below the
downstream water surface. If the differential head is
not large enough to provide discharge equal to the
design flow, the branch interceptor should be
redesigned, or a larger gate used.
After selecting the gate opening required to pass
the peak dry-weather flow, the minimum gate
opening during wet-weather periods should be
determined. This is done by the trial and error
method using the following steps: (1) Assume
diverted discharge; (2) determine downstream water
surface; (3) determine differential head; (4) select
opening from Fig. 2.8.2 for differential head nearest
the assumed discharge; and '(5) repeat until the
assumed discharge is close to the discharge selected
from Fig. 2.8.2 and approximates the design diverted
flow.
Sample computations are given in paragraph
2.8.4. The given conditions are the same as those used
in the sample computations for the manually
operated gate. It should be noted that the ratio of
peak wet-weather flow (WWF) to average dry-weather
flow (DWF) is 4.9 for the tipping gate, compared to
6.8 for the manually operated gate. For this reason
the tipping gate is considered preferable to the
manually operated gate.
The hydrauk'c profile for the design diverted flow
of 2 cfs is given in Fig. 2.8.4.2. The hydraulic profile
for the maximum diversion of 2.45 cfs in storm
periods is shown in Fig. 2.8.4.3. Fig. 2.8.4.1
illustrates the hydraulic conditions affecting the gate.
At the diversion equal to the peak dry-weather flow
of 2 cfs, the differential head (A) is 0.4 feet and the
gate opening is 5.0 inches. When the differential head
(C) is 0.9 feet, the upstream head is 2.0 feet and the
gate begins to close. When the flow reaches its
maximum elevation of 19.6 feet in the combined
sewer the differential head (B) is 2.89 feet, the
opening in the gate has been reduced to 2.56 inches
and the flow diverted to the interceptor through the
gate is 2.45 cfs.
2.8.3 Design Formulas
In connection with their contract for furnishing
tipping gate regulators to the Wyoming Valley
Sewerage Project, the Rodney Hunt Company, was
required by Albright and Friel, the project engineers,
to have the gate calibrated by laboratory test. These
tests were made at the Alden Research Laboratories,
Worcester Polytechnic Institute, Worcester, Mass. The
following charts from this report are reproduced
through the courtesy of the Wyoming Valley
Sewerage Authority.
a. Figure 2.8.2 shows the relation between
discharge through a 12-inch wide gate and the
differential head between the water levels
upstream and downstream level constant at 10,
16, 22, and 28 inches and varying the upstream
head. Where two curves are shown for a given
opening the lower curve represents the flow for a
downstream elevation of 10 inches. Otherwise
51
-------
TIPPING GATE CHAMBER^?
TIPPING GATE
COMBINED SEWER
4A"
OVERFLOW
DIVERSION
CHAMBER
PLAN
SECTION "A"-"A" ALONG CHANNEL
TYPICAL LAYOUT
TIPPING GATE REGULATOR
Courtesy Rodney Hunt Co.
52
-------
FIGURE 2.8.1.2
SECTION "A"-"A"
(A) BOTTOM PLATE
(g) BOTTOM PLATE ADJUSTING SCREW
© SLOTTED STOP
(5) TRUSCON INSERTS
© STOP LUG
© GATE LEAF
(5) BEARING
® COUNTER-WEIGHT
(3) BAFFLE PLATE
PHI CAST CONCRETE HOUSIN*
POSITION OF BATE
DURIN* STORM PLOW
CONDITIONS
POSITION OP «ATE
OURIN* OMV WEATHER
FLOW CONDITIONS
J
CROSS-SECTION
BACK VIEW
TIPPING GATE
USED AT MILWAUKEE
Courtesy Rodney Hunt Co.
53
-------
FIGURE 2.8.1.3
STOP DISC BOLT
STOP LINK
TIPPING GATE
USED BY ALLEGHENY COUNTY
SEWAGE AUTHORITY
Courtesy Rodney Hunt Co.
54
_
-------
FIGURE 2.8.2
V)
u.
u
z
o
_l
U.
O
Courtesy Rodney Hunt Co. and Alden Research Laboratories
55
-------
FIGURE 2.8.3
Courtesy Rodney Hunt Co. and Alden Research Laboratories
56
-------
the curves represent the average of the data for
all downstream heads.
b. Figure 2,8.3 shows upstream water levels at
which the gate starts to close and to open. From
these data it is apparent that the upstream depth
must be about 2 feet before the gate starts to
close and the difference in head may vary
between 0.2 feet and 1.5 feet depending upon
upstream and downstream levels. The data on the
elevations at which the gate started to open were
obtained by stopping all inflow to the chamber
upstream of the gate. Since this condition is not
likely to occur in the field, these data are
considered to have little'significance in the design
of the gate.
For design purposes similar charts should be
obtained from the gate manufacturer for the various
size gates to be used.
2.8.4 Sample Computation
Tipping Gate
Pertinent data
D = diameter
Q = quantity of flow
d = depth of flow
V = velocity
S. = slope
interceptor sewer
D = 36", Invert el. = 10.0
Water surface =12.4
Combined sewer - Design Q = 100 cfs
D = 54", Invert el. = 16.0, S = 0.0026
Manning n = 0.013, V = 6.4 fps (full)
Flow
DWF = Dry-weather flow1 - av
Dry-weather - peak
1-year storm
10-year storm
Q
cfs
0.5
2.0
60.0
100.0
d
ft.
0.3
0.5
2.5
3.6
V
fps
1.8
2.5
6.7
7.2
WS
16.3
16.5
18.5
19.6
Distance from interceptor to regulator 100'
HGL = hydraulic grade line
EL = energy line
Design Q = 2 cfs
Branch Interceptor
L = 100' n = 0.013 Dia. = 10"
s = 0.008 V = 3.7 fps (full-
V at 0.8 depth = 1.13 x 3.7 = 4.2 fps
V2/2g = 0.27
57
-------
FIGURE 2.8.4.1
CHART
A- AH»O
•-AHs9
BASED ON
4* BATE 0
O ATE O
SAMPLE
'ENtNO >
E-MlMft-
ro CLOSE
MAX. UPST CAM DEPTH
WS UWTWEA • OF SATE
COMBINED 9 EWEft
WS UP9THE M OF BATE
DIVCBTI 0 FLOW
HYDRAULIC CONDITIONS
FOR TIPPING GATE
58
-------
FIGURE 2.8.4.2
1 rr
0_?5
- Ulg
'sjj
^ ¥
/"^ -\
HYDRAULIC PROFILE
FOR 2 CFS
TIPPING GATE REGULATOR
59
-------
2.8.4 Tipping Gate
Diversion dam elevation
= 16.0 + 0.5 = 16.5
Try 12" gate Figure 2.8.2
For 5.0" opening and 10" tail water differential head = 0.40'
Downstream WS = 16.5 - 0.4 = 16.1'
In Figure 2.1.3.1 for vertical orifice, downstream W.S. is
15.92. Therefore lower branch interceptor by 16.12 — 16.10
= 0.02 from that shown in Figure 2.1.3.1.
Branch Interceptor
Downstream invert
14.25 - 0.02
Neglect critical depth 14.23
+ 0.8 (0.83) = 14.23 + .66
V2/2g = 0.27
Friction loss 100 x 0.008 = 0.80
Upstream end
Entrance loss 0.5 V2/2g = 0.14
Neglect friction and bend loss in chamber
Set chamber invert 10" below
WS 16.10-0.83
differential head = 16.50 - 16.10 = 0.40
.-. Q = 2.0 cfs for 12" gate and 5.0"
opening from Figure 2.8.2
ELEVATION
Invert HGL EL
14.23
15.03
15.03
15.27
14.89
15.69
15.83
15.16
15.96
16.10
16.10 16.10
Determine diverted flow in storm period
HGL in combined sewer
Q diverted-cfs assume
10" branch S =
Lower end top elev. 1_/
10-year storm 1-year storm
19.60
2.4
0.012
18.50
2.2
0.010
1_/ This neglects critical depth at lower end and assumes
HGL is at top of pipe.
60
-------
FIGURE 2.8.4.3
HYDRAULIC PROFILE
FOR 2.45 CWS
TIPPING GATE REGULATOR
61
-------
2.8.4 Tipping Gate
10-year storm 1 -year storm
Exit loss V2/2g
Friction loss 100 x s
Entrance loss 0.5 V2 /2g
HG downstream of gate
differential head on gate
12" gate 2.56" opening Q =
Diverted Q = WWF
WWF _ WWF
DWF 0.5
Ratio
0.30
1.20
0.15
16.71
2.89
2.5
2.45
4.9
0.25
1.00
0.12
16.43
2.07
2.1
2.15
4.3
2.9 Cylindrical Gates
2.9.1 Description.
An isometric diagram of the cylindrical gate is
shown in Fig. 2.9.1. Combined sewer flow is diverted
by a dam through an opening in the side of the sewer
into the gate Chamber. The diverted flow drops
through the horizontal orifice to the intercep&r.
The operation of this device, when controlled by
the sewage level in the branch interceptor, is shown in
Figures 2.9.1B and 2.9.1C. When the level in the
interceptor is low, as in Fig. 2.9.1B, the air-vent pipe
prevents the formation of a vacuum in the interior of
the gate and the gate stays open. When the level in
the interceptor rises to a predetermined elevation, the
sewage blocks the air-vent pipe, as shown in Fig.
2.9.1C. The entrainment of air produces a vacuum in
the interior of the cylindrical gate and atmospheric
pressure forces the gate down and closes the orifice.
The control of the gate by the sewage level in the
combined sewer is shown in Figures 2.9.1D and
2.9JE. When the level in the sewer is low the
counterweight keeps the gate open, as in Fig. 2.9.1D.
When the sewage level rises, the weight of the liquid
on the conical part causes the gate to lower and close
the orifice
DYNAMIC REGULATORS-AUTOMATIC
2.10 Cylinder-Operated Gates
2J0.1 Description
The cylinder-operated gate may consist of two to
four chambers: (1) A diversion chamber; (2) a
regulator chamber containing sluice gate, cylinder and
float or bubbler tube; (3) an equipment chamber
when electrical equipment is required; and (4) a ti.de
gate chamber, if required. On some deep and large
chambers the diversion and flap gate chambers may
be combined, but the other chambers should remain
separate. Whenever possible it is desirable to
construct the equipment chamber above ground.
The diversion chamber contains an overflow dam
to divert the DWF into the adjacent regulator
chamber. The top of the diversion dam is usually set
to minimize the raising of the fiowline upstream of
the regulator during storm flows and prevent back
flooding. The diversion channel invert is establised so
that the peak DWF will be diverted without
overtopping the dam. During wet-weather periods the
excess flow goes over the dam to the tide gate
chamber and thence to receiving waters. The opening
between the diversion chamber and tide gate chamber
is equipped with one or more tide gates.
The regulator chamber provides for a
cylinder-operated sluice gate which governs the
amount of flow to the interceptor. The action of the
cylinder is related to the sewage level in the sewer by
a sensing device which can be sensitive to either
upstream or downstream flow conditions. The latter
location is used if the main object of the regulator is
to avoid overloading the interceptor and treatment
plant. Generally, the sensing device is a float or a
bubbler-tube. The cylinder is operated either by
water, air or oil pressure. Floats may be used in
conjunction with cylinders operated by water
pressure to avoid the addition of compressed air
equipment. During dry-weather periods the sluice
gate is fully open. In wet-weather periods the rising
sewage level will raise the float or increase the
pressure in the bubbler tube so that the gate will
partially close. The float or bubbler tube is located in
62
-------
FIGURE 2.9.1
GATE CHAMBER
BRANCH ,
INTERCEPTOR )
flexible
B
I
'flexible
W//A
^^
t2l ^
APPLICATIONS OF CYLINDRICAL GATE
COMBINED
SEWER
Courtesy Neyrpic Canada Ltd.
63
-------
a special well connected to the flow channel by a
telltale passage.
When the sensing device is located downstream of
the gate it is generally necessary to install a control
device to maintain subcritical flow in the regulator
chamber. One control which is satisfactory is vertical
timber stop logs used to decrease the channel width.
A vertical slide gate also can be used as a control to
act either as a weir or an orifice on the bottom of the
channel. The use of vertical wood stop logs has the
advantage that the width of channel opening can be
adjusted in the field, and there is nothing to impede
the discharge of debris which may be carried on the
bottom of the channel or may be floating on the
surface of the flow.
While the hydraulics of the regulator can be
computed, adjustments are usually required in the
field to accommodate actual flow conditions. Usually
the float or bubbler tube is set to act when the flow
level is about one inch above the actual peak
dry-weather flow line to insure that all sanitary flow
in dry weather is diverted to the interceptor.
Water used as a pressure medium is usually
obtained from the public water supply. Prevention of
cross-connection hazards will require the use of check
valves, vacuum breakers, and air breaks in drain lines,
based on effective design criteria. Since the pressure
in the water system may vary, the hydraulic cylinder
is usually designed to operate on a minimum pressure
of 25 psi. For small gates this pressure is adequate but
for large gates a very large hydraulic cylinder would
be required. None of the hydraulic cylinder
manufacturers will guarantee cylinders for water
operation. Therefore, the gate manufacturer is
required either to build the cylinder or go to a
speciality manufacturer for it. The chief advantage of
the use of water is that no electrical power is required
and, hence, the regualtor functions during power
failures, and a spearate chamber is not needed for
installation of air compressors or electrical
equipment. Tightening of the packings around the
piston rod and tail rod, if overdone, may increase the
friction forces. Sometimes valves become inoperative
due to rust or scale in the water supply. To prevent
this a strainer should be installed in the supply line.
Maintenance checks are necessary to insure that
clogging of the strainer does not cause gate
malfunctions.
When air is used as a medium for operating the
gate a separate chamber is provided for the air
compressors and electrical equipment. Air has been
used at pressures of 90 to 100 psi. The disadvantages
of this system are: (1) Electrical power is required
which is subject to failure; (2) a separate chamber
must be provided to house the- electrical and
compressed air equipment; and (3) difficulty is
experienced in maintaining electrical equipment in
subsurface chambers. Some jurisdictions using air
pressure for cylinder operation have converted to oil
pressure.
Recent practice in cylinder-operated gates seems
to favor oil as a medium rather than air or water. Oil
has been used at pressures of 350, 750, and 3000 psi
but pressures from 600 to 750 psi are favored. To
reduce corrosion, a separate chamber, preferably
located above ground, is provided for electrical and
pumping equipment. The use of oil results in less
corrosion of valves and cylinders than the use of air
or water. Smaller cylinders are needed to operate the
gate due to the higher pressures used. The
disadvantages are similar to those listed for air
cylinders.
A typical plan of a cylinder-operated sluice gate
regulator using water pressure is shown on Fig.
2.10.1.1. A schematic diagram of a cylinder-operated
sluice gate regulator using water pressure is shown in
Fig. 2.10.1.2 and one using oil pressure in Fig.
2.10.1.3.
The water-pressure operated cylinder, as shown
in Fig. 2.10.1.2, functions basically as follows: (1)
Water supply is usually obtained from a public water
supply system which should be protected with
adequate backflow prevention devices; (2) cylinders
should be sized and designed for actual pressure of at
least 5 psi less than minimum available pressure
specified by the user; and (3) water pressure on the
cylinder is controlled by a 4-way valve of the vertical
plunger type which is actuated by a float in a well
connected to the channel downstream of the sluice
gate.
There are four pipe connections to the 4-way
valve: (1) From the water supply; (2) to waste; (3) to
the top of the hydraulic cylinder; and (4) to the
bottom of the hydraulic cylinder. In dry-weather
periods the float is down, the valve is up and the
water pressure is supplied to the bottom of the
hydraulic cylinder to keep the sluice gate wide open.
During storm periods when the flow line in the
channel reaches a predetermined level, the float rises,
causing the 4-way valve to lower. This results in
admission of water pressure in the bottom of the
cylinder, thus causing the sluice gate to close. As the
discharge through the .orifice decreases the flow line
in the regulator chamber falls, causing a reversal of
this procedure. Thus the gate will "hunt" for its
proper position. A needle valve is used to control the
64
-------
FIGURE 2.10.1.1
REGULATOR CHAMBER
PLOW TIDE GATE
FLOW
<*
BRANCH
INTERCEPTOR
SEWER
COMBINED SEWER
PLAN
MAH
FLOW^
7^
y
y
^
i
/
^y yy yy / y y y y y y1^
REGULATOR CHAMBER
/VERTICAL STOP LOGS
1 , I AFLOAT WELL
yyyyyyyi
DIVERSION
CHAMBER
y^Z
y
i
i ^
| FLOW
^
COMBINED
SEWER
BRANCH INTERCEPTOR SEWER
CYLINDER-OPERATED GATE
65
-------
FIGURE 2.10.1.2
PUBLIC SI/
WATER
SUPPLY
4-WAY VALVE
FLOAT
GATE OPEN
GATE CLOSING
SCHEMATIC DIAGRAM
CYLINDER-OPERATED GATE
(WATER ACTUATED)
CYLINDER
25 PS I WIN.
GATE
CYLINDER
25 PSI MIN.
SATE
66
-------
FIGURE 2.10.1.3
SCHEMATIC DIAGRAM
Q'
6
FLOW
IO
1
2
3
4
5
6
7
8
9
IO
OIL RESERVOIR
ACCUMULATOR-OIL UNDER CONSTANT AIR PRESSURE
AIR COMPRESSOR
BUBLER TUBE
FOUR-WAY VALVE
OIL LINES TO POSITIONER a CYLINDER
ELECTRIC CONTROL
POSITIONER
HYDRAULIC CYLINDER
GATE
CYLINDER-OPERATED GATE (OIL ACTUATED)
-------
rate at which the water pressure is transmitted to the
cylinder to prevent rapid up-and-down movements of
the gate. The usual installation will involve a vertical
movement of the float of three inches and of the
4-way valve of.3/4 inch.
A cylinder-operated gate using oil pressure, as
shown in Fig. 2.10.1.3, functions as follows: An air
compressor supplies air continuously to a bubbler
sensing device located downstream of the gate. The
pneumatic pressure on the bubbler-tube is
transmitted to a "positioner" on the cylinder. Oil is
fed by an electric-motor-driven pump to the
accumulator where the oil is kept under pressure by
air supplied from the air compressor. When the
position of the gate is out of balance with the level
indicated by the bubbler-tube a signal from the
positioner actuates a pneumatically operated
four-way valve in the hydraulic control, which directs
the oil to the top or bottom of the cylinder as
required to open or close the gate.
Regulators of this type have been installed
without a "positioner." Its use results in less
"hunting" by the gate and is recommended.
A manual or diesel operated pump should be
provided for gate operation in case of power failure.
The major advantage of this regulator is that the
gate position can be transmitted to a remote control
point either by a pneumatic signal, for distances up to
800 feet, or by an electrical signal to any distance.
Such a system can also permit positioning of the gate
from the remote control point.
2.10.2 Design Guidelines.
Obtain all pertinent data for the combined sewer
at the proposed location of the regulator. This will,
include diameter, invert elevation, slope, average and
peak dry-weather flow and peak storm flow. Obtain
similar data for the interceptor at the proposed
location of its junction with the branch interceptor.
Also obtain data on high water levels in the receiving
waters. If the interceptor is being designed in
conjunction with the regulator, assume an elevation
for the interceptor and adjust as found necessary by
subsequent computations for the regulator.
After making a preliminary layout the energy and
hydraulic grade lines should be computed for the
branch interceptor, regulator and combined sewer.
Insofar as possible, the designer should select
elevations that will result in uniform flow. If
non-uniform flow occurs it may be necessary to
compute backwater or drawdown curves.
Initial design should be made on the basis of
diverting the maximum dry-weather or peak sanitary
flow, when peak sanitary flow occurs in both the
interceptor and branch interceptor. The elevation of
the water surface in the combined sewer as thus
computed should be below the elevation of the
diversion dam, which usually is established as six
inches above the invert of the combined sewer. The
sizes and elevations of the proposed structures should
be adjusted as necessary so that this computed water
surface is just below the dam elevation.
The hydraulic and energy grade lines also should
be determined for the maximum storm flow and peak
sanitary flow in the combined sewer and peak
sanitary flow in the interceptor. If the receiving
waters into which the combined sewer discharges are
subject to variation in elevation the effect of this
variation should be included in the computations.
Good design requires that the water surface in
the float well will be dependent on the flow through
the sluice gate and not be affected by flow conditions
downstream in the branch interceptor or interceptor,
and the diversion chamber and tide gate, if used, will
not raise the water surface in the combined sewer
during storm flows to an extent that damage from
flooding will occur upstream of the regulator. If there
are downstream constraints on the interceptor and if
excessive flows are diverted to the interceptor, it may
be possible for the hydraulic gradient to rise
sufficiently in the regulator chamber to cause the
float to close the sluice gate completely, thus
eliminating all flow interception.
2.10.3 Design Formulas
The sample computations given are based on the
hydraulic formulas outlined below. The designer may
wish to analyze the problem in more detail than is
given, by reference to texts on hydraulics.
As a result of turbulent flow in the regulator
during periods of peak flow and because of clogging,
it is doubtful if any regulator will act exactly as
designed. The designer must use judgment as to how
precise his computations shall be made. The following
are design considerations:
a. Friction losses in pipes and channels.
Friction losses in the computations herein
are based on the Manning formula using a
constant n friction coefficient with variation
in depth.
b. Contraction or inlet loss.
H = K(V22/2g-V12/2g)
where H = head loss in feet
K = 0.5 for sharp-cornered entrance
K = 0.1 for gradual transition
Vi = upstream velocity in fps
V2 = downstream velocity in fps
c. Enlargement or outlet loss
68
-------
FIGURE 2.10.4
UJ
oc
0>
0.
0. O
O <
s
UJ
O
ui
»-
o
(9
O
a
o
0)
9
/
^
••t
*
0
tn
^ <
HYDRAULIC PROFILE FOR REGULATOR
WITH CYLINDER-OPERATED GATE, Q OF 30 CFS
69
-------
= K(V,2/2g
V22/2g)
where H = head loss in feet
K = 1 .0 for sudden enlargement
K = 0.2 for gradual transition
Vi = upstream velocity in fps
V2 = downstream velocity in fps
d. Loss in 90-degree bend
H = 0.25-V2/2g
where H = head loss in feet
V = velocity in fps
e. Flow through orifice
where H = head loss in feet
Q = discharge in cfs
A = area of orifice in square feet
C = 0.7 for sluice gate or vertical orifice
C - 0.6 for horizontal plate orifice
f. Discharge through opening between vertical
stop planks
Q = 3.09bH3/2
where Q = discharge in cfs
b = opening width in feet
H = total head upstream of stop planks
The above is applicable only if the downstream
water depth is 2/3 or less of the upstream head.
g. Critical depth.
Critical depth may be determined for
rectangular and circular conduits from Fig.
26 and for circular conduits from Table XVI
both of which are in ASCE Manual No. 27.
h. Backwater and drawdown curves.
these curves may be computed by either of
the methods illustrated in Tables XV and
XVI in ASCE Manual No. 27.
Pertinent data
2.10.4 Sample Computation
Cylinder-Operated Gate
Interceptor sewer
D = 60", Invert = el. 10.0, W.S. = el. 14.0
Combined sewer
D = 60", Invert = El. 17.0, S - 0.0022
Manning n = 0.013 V (full) = 6.2 fps
DWF = Av. dry«weather
Peak dry-weather
Peak storm *
cfs
15
30
120
d
ft.
1.20
1.70
4.00
W.S.
18.20
18.70
'21.00
V
fps
4.3
5.2
7.0
1 Includes peak dry-weather flow
Distance from interceptor to regulator on combined sewer is 100 ft.
For hydraulic profile see Figure 2.10.4
HGL = hydraulic grade line
EL = energy line
D = diameter, V = velocity, Q = discharge
d = depth of flow
S = slope
L = length
70
-------
2.10.4 Cylinder-Operated Gate
Interceptor — Peak dryweather flow
Branch Interceptor n = 0.013
D = 30in., Q = 30cfs, s = 0.0054
d = 0.8 x 2.5 = 2.0 ft.
V = 1.13 x 6.2 fps
V2/2g = 0.76ft.
Lower end
Pipe outlet loss 1 (0.76 - 0) = 0.76
Upper end
Friction loss 100 x 0.0054 = 0.54
ELEVATION
Invert HGL EL
10.00 14.00
12.00 14.00
14.76
12.54 14.54 15.30
Regulator Chamber
Say b = 2.5 ft., d = 2.0 ft.
V = 30 = 6.0 fps
2.5 x 2.0
V2 /2g = 0.56
Pipe inlet loss = 0.5 (0.76 - 0.56) = 0.10
HGL = 15.40 - 0.56
Invert = 14.84 - 2.0
Determine if flow is stable from Figure 26 ASCE
Manual 37
Q = 30 cfs b = 2.5 feet
dc/b = 0.65
dc = 0.65x2.5 = 1.62
2.0 = 1.24 > 1.15 Flow is stable
1.62
However to reduce chance of backwater effect from
interceptor raise flow line 1.0 foot by inserting
vertical stop logs in channel
12.54 14.54 15.30
12.84
d = 3.0 feet
V = 3.0
2.5 x 3.0
V2/2g = 0.25ft.
= 4.0 fps
14.84
12.84 15.84
15.40
16.09
71
-------
2.10.4 Cylinder-Operated Gate
Determine stop log opening
Q = 3.09 b H 3/2
30 = 3.09 x b x (3.0 + 0.25)3/2
b= 1.65 feet (opening)
Condition upstream stop logs
Channel friction loss
L = 10ft. n = 0.015
V = 4.0fps r = 0.88
From nomograph S = 0.0018
Friction loss = 10 x S = 0.02
Assume complete loss of velocity of discharge from
sluice gate from impact on granite slab:
Upper end of channel
ELEVATION
Invert HGL EL
12.84 15.84 16.09
12.84 15.86 16.11
12.84 16.11 16.11
Regulator Chamber
Head loss in sluice gate
Try 30 in. x 24 in.
Q =CAV2gH
30 = (0.7) (2.5) (2.0) (8.03)
H =1.04 ft.
Diversion Chamber
Invert =16.11 -2.0
16.11 + 1.04
Approach Channel
b = 2.5 ft.
d = 17.15 -14.11 =3.04 ft.
V= 30 =4.0fps
2.5 x 3.0
= 0.25
Neglect friction loss in channel
Bend loss 0.25 (0.25) = 0.06
Required upstream of bend
Available in combined sewer
Dam elevation 17.00 + 0.5 = 17.50
> 17.21 Design OK
14.11
17.15
17.40
14.17 17.21 17.46
17.21 17.46
17.00 18.70 19.12
72
-------
2.10.4 Cylinder-Operated Gate
Determine sluice gate opening during peak storm
Q =120 cfs in combined sewer
HGL =21.00 in combined sewer
H =21.00-16.11 =4.89 ft.
Q
Q
= CAV2gH
= 30 cfs through sluice gate
30 = (0.7) (2.5) (d) (8.03) V 4.89
d = 0.97 ft. — height of gate opening
Thus gate travel is 2.0 — 0.97 = 1.03 ft.
The following adjustments could be made in the foregoing design. Since the computed
HGL in the diversion chamber is 0.29 feet (17.50 -17.21) below the top of the dam the invert
of the structure between the diversion chamber and the stop logs could be raised 0.29 feet.
Since the stop logs control flow upstream thereof, the HGL downstream of the stop logs could
be lowered by decreasing the length and/or increasing the diameter of the branch interceptor.
Since the drop in EL at the stop logs is 0.69 feet (16.09 - 15.40) any rise in water surface of
the interceptor exceeding 0.69 feet will result in backwater effect on the regulator.
2.11 Motor-Operated Gates
2.11.1 Description.
A regulator using a motor-operated gate consists
of two to four chambers; (1) A diversion chamber;
(2) regulator chamber containing the sluice gate and a
sensor; (3) a motor chamber; and (4) a tide gate
chamber, when required. On some deep and large
chambers the diversion and tide gate chambers may
be combined but the other chambers should remain
separate. Whenever possible it is desirable to
construct the motor chamber above ground. The
diversion chamber is as described for
cylinder-operated gates in 2.10 of this Section.
The regulator chamber contains a motor-operated
sluice gate which governs the amount of flow diverted
to the interceptor. The action of the gate relates to
the sewage level by a sensing device which can be
used to respond to flows either upstream or
downstream of the sluice gate. The latter location is
used if the main object of the regulator is to avoid
overloading the interceptor and treatment plant. The
sensor could be a sealed electrode type, pressure cell
type or possibly pressure-sensitive electric type. A
float or compressed-air bubbler tube could also be
used. The design of the regulator chamber is similar
to that of the cylinder-operated gate (see 2.10.)
2.11.2 Design Guidelines.
Guidelines for hydraulic design are the same as
those for the cylinder-operated gate. Design formulas
for sample computations for this regulator are as
indicated for the cylinder-operated gates.
2.12 External Self-Priming Siphon
2.12.1. Description
This device is currently in use in Europe and is a
new flow control method which could lend itself to
"total systems control."
The external self-priming siphon uses an exterior
device to prime the siphon and the design of the
siphon conduit is not as critical. A siphon of this
type, as shown in Fig. 2.12.1, was proposed by A.
Moan and Y. Ponsar of France, for use as a
flood-stage or tide-water check valve (tide gate) to
protect the interceptor. -When the upstream water
surface is higher than the downstream water surface
the sewage will flow through an orifice plate in the
top of the priming tube and through the priming tube
to the downstream side. This flow will carry air with
it, causing a partial vacuum on the underside of the
orifice. By connecting the summit of the siphon to
the priming tube, a vacuum is created on the siphon
summit, causing the siphon to discharge. To prevent
siphonage in the opposite direction a float and air
valve device is provided so that when the downstream
level raises the float an air valve is open, allowing air
at atmospheric pressure to enter the summit. The use
of this type siphon with a "Ponsar Regulator" as a
73
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FIGURE 2.12.1
AIR FILTER
SPONSAR REGULATOR
FLOATER
LEVEL SENSING
PIPE ASSEMBLY
SNUBBER
ORIFICE
CLEAR WATER
IN FLEXIBLE
PLASTIC BULB
(RISES TO HEAD
ON WEIR)
LEVEL SENSING TUBE
VACUUM Ot OR DP
TOP OF ORIFICE
MUST BE ABOVE
CROWN OF INLET
SEWER
OUTLETS MUST
BE SUBMERGED
CLEAN OUT GATE
(MANUAL)
PONSAR SIPHON
Courtesy Degremont S.A. and New York City, N.Y.
74
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combined sewer regulator is described in subsequent"
paragraphs.
The Ponsar siphon also has been used in waste
water treatment plants but, so far as is known, has
not been used in either the United States or Canada
in connection with combined sewer regulators. The
treatment plant in Geneva, Switzerland, utilizes this
type of siphon- to automatically distribute flow
equally to the remaining number of treatment units
in operation if one or more is taken out of service,
and to divert flows in excess of fixed maximums to
other units of the treatment plant.
Its use also has been suggested for diverting a
predetermined amount of combined sewer flow to a
plant, as shown in Fig. 2.12.1. The minimum flow
that can be diverted by this type of siphon is
governed by the fact that, to prevent clogging, the
priming tube should have a minimum diameter of
eight inches and the orifice a minimum diameter of
five inches. Using these, sizes the application of the
Ponsar siphon to diversion flows less than 8 cfs would
not seem practical.
The priming 'tube is used to develop negative
pressures in the siphon summit. If the inlet and outlet
branches of a siphon are submerged, a priming tube
can be utilized effectively to establish siphonage,
provided air evacuation velocities are developed in the
priming tube and its cross-sectional area is large
enough to pass suspended materials transported by
the incoming waste water flow.
Upon establishment of appropriate vacuum
conditions within the siphon, the water column will
rise to the summit of the siphon and flow will be
established over the siphon crest or weir into the
discharge branch. By controlling the intensity of
vacuum conditions within the siphon, the discharge
can be effectively regulated to desired discharge
limits.
Basic Components:
The siphon installation comprises three basic
elements: (1) An upflow branch with a priming tube
within the upflow branch; (2) a vacuum chamber
with- a vacuum regulating device; and (3) a discharge
branch. A self-contained siphon installation
incorporating these basic elements is shown in Fig.
2.12.1.
The priming tube consists of a priming pipe with
an orifice plate attached at the top. The orifice is set
at a level high enough above the crown of the inlet
sewer to assure continuously complete submergence
at entry to the siphon upflow branch. The lower end
of the priming pipe extends to the flow level of the
receiving conduit where it must be submerged below
the lowest downstream discharge level.
The orifice serves to establish a jet discharge
which draws entrapped air from the space directly
under the orifice, surrounding the jet contraction,
and from the siphon summit through an air suction
pipe installed for that purpose. The air and waste
water mixture is drawn down the priming pipe where
the air escapes to the downstream water surface. The
rate of air evacuation tends to increase with the
length of the priming pipe. The pipe connection from
the siphon summit to the priming pipe, immediately
below the orifice serves to remove air from the siphon
initially and after full flow is established.
Consideration of Flow Conditions
in Priming Pipe
Experimental work reported by Kalinske in
"Hydraulics of Vertical Drains and Overflow Pipes,
Bulletin No. 26, Studies in Engineering, University of
Iowa," provides data on downdraft flow in pipes
roughly comparable to flow conditions in a priming
tube. In accordance with Kalinske's findings, the
maximum ratio of air removal to water flow is
approximately 0.65 when discharging about 1.1 cfs of
water through a 6-inch diameter pipe 6.67 ft. long,
and is approximately 1.0 when the water discharge is
at a rate of 1.0 cfs in a priming tube 11.0 ft. long. For
short pipes of 2- to 3- ft. length, jet flow occurs
without touching the walls of the pipe. The negative
pressure immediately below the pipe entrance
increases with the discharge and length of pipe.
Although longer pipes will produce a higher vacuum
the discharge does not increase correspondingly. In
general, the ratio of head "H" on the priming pipe to
pipe diameter "D" is proportional to the Froude
number, particularly when the priming pipe is not
flowing full. However, the Reynolds number becomes
important when the priming pipe begins to flow full.
The critical values of H/D at which the latter occurs
may be estimated at approximately 0.9 to 1.1 for
pipe lengths ranging from 20 to 50 pipe diameters.
The orifice may be expected to modify the critical
head.
Air bubbles will tend to rise against the
downward water flow at a velocity of approximately
0.75 fps. Therefore, downward current velocities
greater than 0.75 fps must be maintained to evacuate
air. For effective priming, a necessary condition is
that the downflow rate of liquid in the priming pipe
must exceed 1 fps and should preferably be about 2
fps. As air is removed from the siphon an equivalent
volume of water will be drawn up into the siphon and
into the priming tube. Similarly, after flow is
established over the crest of the siphon, more air will
75
-------
be drawn out through the downdraft tube and the
water level will likewise rise in the downdraft tube.
2.12.2 Design of Priming Pipe (Based on data
furnished by Degremont Corp., Paris)
Operation of the priming pipe is similar to a
hydraulic compressor in which hydraulic power is
converted to compressed air power.
Let: Absolute suction pressure at inlet = Pa (ft. of water)
Discharge pressure due to submergence at outlet
= P (ft. of water)
Ratio of pneumatic to hydraulic power = u
Air compression rate = (Pa+ P)/Pa
Output ratio of volume of air to volume of water
= Qa/Qw
Available operating hydraulic head = h
Then:u = (34Qa)/(h Qw) x I0ge (Pa+ P)/Pa
For priming 'tubes the ratio of (air power)/(water
power) "may be estimated at 40 percent.
The hydraulic air compressor may be considered
the reverse of an air lift and the design could proceed
on that basis. The relationship of available operating
hydraulic head, depth of submergence at outlet,
specific gravity of air plus water mixture and
hydraulic losses may be expressed as follows: (based
on "The Control of Water" by Philip A. M. Parker.)
(h + d)/(l + K) -d = hf+hv
Where:
Available operating hydraulic head = h (ft)
Depth of submergence at outlet = d (ft)
Losses due to friction = hf (ft)
Misc. other head losses = hv (ft)
K = (34Qa)(dQw) x I0ge x (34+d)/34
In the above value of "K" the air supply is
measured hi cu. ft. at atmospheric pressure. In this
connection it may be pointed out that 1 (1 + K) is
the specific gravity of the air + water mixture.
The preceding considerations provide a basis for
estimating the air discharge rate, "Qa" and,
correspondingly, the time required to produce the
desired vacuum conditions and the duration of
back-up conditions in the incoming sewer.
The use of an orifice of smaller diameter than the
priming pipe is necessary to provide an initial jet at
downdraft with partial vacuum around the jet below
the orifice.
Control of Flow Through Siphon
The rate of flow through a siphon can be
controlled to any desired limit below the rate of flow
at full siphon action, by introducing air into the
siphon chamber at a regulated rate so as to maintain
the desired partial vacuum for design conditions. This
objective can be accomplished by use of a vacuum
pump with suitable provisions for its operation in
relation to desired flow control. Either electrical
power, or hydraulic power by water under pressure
must be provided to operate the air pump.
An automatic, self-regulating device with
appropriate accesories described as the Ponsar
Regulator is available to perform the function of
vacuum regulation inside the siphon without the use
of external power.
The Ponsar Regulator is essentially a
vacuum-operated, float-balanced air valve which
responds to the vacuum intensity and liquid level in
the siphon chamber. The air valve is normally closed.
It opens only to admit air in response to siphon
conditions, as required to maintain the design flow
and to prevent vacuum intensity in excess of desired
design conditions.
The Ponsar Regulator consists of two basic
elements: (1) A regulator valve which has a floater at
the top of the valve immersed in oil over a mercury
seal and a connecting shaft to an air inlet valve at the
bottom; and (2) a level sensing pipe assembly with its
lower end inside a separate chamber where a
water-filled plastic bag is attached at the bottom. A
level-sensing tube is installed inside the level-sensing
pipe. The top of the pipe has an airtight joint where
the level-sensing tube passes to the outside. As the
water level within the siphon rises due to increased
vacuum conditions, the liquid in the plastic bag is
compressed, raising the water level in the pipe until
the mouth of the level sensing tube is submerged.
Filtered air is drawn in through an air filter and a
small orifice at the top of the level sensing tube. The
quantity of air drawn in is dependent on the water
level in the level sensing pipe. This air lowers the
vacuum pressure in the level sensing tube and the
reduced pressure is transmitted to the top of the
floater. The lower part of the air valve has a tube
connection to the top of the level sensing pipe,
thereby maintaining vacuum conditions therein equal
to the vacuum in the siphon. As the vacuum pressure
increases, the water level in the siphon rises above the
design level, the air valve is subjected to a higher
vacuum intensity than the top of the float, the air
valve "descends, its air ports are opened, and air is
admitted to the siphon until the vacuum intensity is
reduced and the design flow level is restored.
For purposes of discussion, the vacuum suction
pressure at the top of the float is designated Df and
the vacuum suction pressure in the siphon as Ds. If
the air inlet orifice at the top of the level sensing tube
becomes clogged or its diameter is too small to admit
sufficient air, then Df will approach Ds and the air
76
-------
valve will open, because the buoyancy of the floater
is greater than the weight of the moving valve element
by a vacuum pressure differential, X, equivalent to a
predetermined value. Whenever Ds exceeds Df plus X,
the air valve opens. The air valve remains closed as
long as Ds is less than Df plus X. The level sensing
tube is movable and can be reset to desired design
elevations. A separate indicator gauge is provided to
show the water level in the siphon, which permits
setting the level sensing tube at the proper elevation.
Problems of Siphon Operation
Since siphon operation is governed by partial
vacuum conditions, some air will always remain at its
summit. It also can be expected that additional air
will be introduced by release of entrained air in the
incoming waste water flow and by direct inward
leakage at siphon joints and connections. However,
air admitted by the regulating device will be the
major air component.
Changes in upward velocities of the siphon flow
may cause some surging at the water surface. It is
impractical to completely suppress surging effects
inside the siphon, except as can be accomplished by a
snubber provided in the level-sensing tube above the
clear water container.
In general, the.lower range of operation, to about
1/3 of the full siphon capacity, will be unstable in
action because of inadequate air evacuation at low
flows. Greater stability will prevail when the siphon
operates at 2/3 or greater capacity.
Flow conditions in the incoming sewer will be
affected by operation of the siphon. In order to
prevent entry of air from the incoming sewer to the
upflow branch of the siphon, entry to the siphon
must always be submerged. The top of the priming
tube therefore must be set higher than the inside top
of the sewer connection entering the siphon.
Additional backup in the sewer will be caused by the
head required above the orifice to establish effective
air evacuation and necessary vacuum conditions. The
backup of flow will result in a temporary reduction
of flow velocities and temporary storage in the
incoming sewer. After appropriate vacuum pressures
are established in the siphon; the flow in the sewer
will be restored to normal levels related to submerged
inlet conditions.
77
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SECTION 3
DESIGN GUIDELINES FOR TIDE GATES, THEIR
CHAMBERS AND CONTROL FACILITIES
CONTENTS
Page
3.1 General Information
3.2 Design
3.3 Sample Computation
81
87
91
79
-------
-------
3.1. General Information
3.1.1 Principle
Tide gates, also called backwater or flap gates, are
installed at or near sewer outfalls to prevent the
back-flooding of the sewer system by high tides or
high stages in the receiving waters. Tide gates are
hinged at the top and are designed to permit
discharge through the gate with small differential
head on the upstream side of the gate and to close
tightly with small differential head on the
downstream side of the gate.
3.1.2 Application
Tide gates are required at all sewer outfalls where
there is a possibility of the sewer system being
flooded by a rise in the level of the receiving waters.
In combined sewer systems without regulators,
tide gates usually are installed at the end of the
outfall. The outfall is terminated in a concrete
headwall and the tide gate is mounted on the face of
the wall. This tide gate location very often makes
maintenance work difficult, particularly if the gate is
partially submerged. In this case, boats may be
required to carry out normal maintenance
procedures.
When regulators are constructed on combined
sewer systems, consideration should be given to
locating the tide gate in a chamber adjacent to the
regulator chamber. This has several advantages. The
gate will be easier to service than when located in or
near the water. The gate can be inspected in
conjunction with maintenance visits to the regulator.
Provision can be made in the chamber for use of stop
logs downstream of the flap gate so that the gate can
be serviced "in the dry" if necessary. A further
advantage of installing the gate in a chamber is that
motorized equipment can.be operated directly over
the chamber for use in maintaining or replacing the
gate.
The chamber width should provide a minimum of
6 inches clearance between the tide gate and the wall.
When multiple gates are used the" post or column
between the gates should have a minimum width of 2
feet.
Shaft and surface openings should be provided
with dimensions of about 1 foot greater than those of
the gate. When the gate is always partially submerged
it may be desirable to install two gates in series to
provide a safeguard against one gate being clogged
open. In the latter case the chamber can be enlarged
to permit this series installation of gates.
3.1.3 Description
Tide gates are available in three types depending
on the material used for the flap as follows: (1) Cast
iron; (2) pontoon; and (3) timber.
Tide gates with cast iron flaps are available within
circular, square or rectangular shapes. Circular flaps
range from 4 to 96 inches in diameter. Sizes available
from one manufacturer are given in Figure 3.1.3.1
Square and rectangular cast iron tide gates are
available in sizes ranging from 8 inches square to 96
inches square. Sizes available from another
manufacturer are shown in Figure 3.1.3.2.
Pontoon flap gates are fabricated of sheet metal
to form a number of air cells. This increases the
buoyancy of the gate and enables it to open under a
smaller differential head than is possible with a cast
iron gate, particularly 48 to 120 inches, as shown in
Figure 3.1.3.3. Square and rectangular shapes are
available in sizes ranging between 48 inches square to
120 inches square as shown in Figure 3.1.3.4.
Type 316 stainless steel is used for large pontoon
fabrications. It is weldable, has physical properties
comparable to mild steel, and has satisfactory
corrosion resistance.
In recent years, there has been a revival of timber
tide gate flaps. This is due in all probability to the
pollution in major harbors. Teredos and ship worms
cannot live in polluted water. Therefore, the timber
will have a long life. Warping is partially prevented by
the use of strong backs bolted to the timbers. These
are -pieces of railroad track that are hot dip galvanized
after all machining is completed. Timber gate leaves
are not as tight as the metal tide gates because it is
difficult to seal the space under the metal seat band
between the timbers.
Timber gates are available in the same sizes as the
larger size cast iron square and rectangular gates. One
manufacturer's models are shown in Figure 3.1.3.5.
Creosoted yellow.pine is frequently used in timber
gates. Recently greenheart timber has been
introduced. This wood grows only in British Guiana,
requires no wood preservative treatment and is
resistant to wood-destroying fungi. It is extremely
dense, weighing approximately 70 pounds per cubic
foot, and is well suited for flap gates as it requires
little additional weight to offset buoyancy
Greenheart also is more resistant to seasoning splits
and checks 'than common structural woods, it
machines well and resists distortion well. The
following table compares the working stresses for
greenheart and other structural woods.
81
-------
FIGURE 3.1.3.1
CAST IRON CIRCULAR FLAP GATES
Anchor bolts In
concrete structure
Mounted to standard
. pipe flange
Anchor bolts In
concrete structure
with concrete pipe
"E" drilled holes on "F" Bolt 1" Grout pad
Circle also available
25 Ib & 125 Ib drilling
"6" Flange thickness
Mounted to cast-iron
wall thimble
METHODS OF INSTALLATION
TABLE OF DIMENSIONS (Inches)
A-Dla.
4
5
6
B C D E F G
9
10
! 11
8 ! 131/2
10
12
14
15
16
18
20
21
24 '
27
30
36 '
42 '
48
54
60
66 '
72
78 ;
84
16
19
5Vu
SVn
SVn
63/4
8'/4 •
93/4
21 | 12
22 12
23'/2
25
27'/2
29
32
35'A
38'/4
46
53
59Va
66'A
73
79
86'/2
93V.
99J/4
96 ! 113'/4
12J/4
14'/2
16V.
16V.
19'/2
21V.
24
28'/2
33
38
42
-------
SQUARE AND RECTANGULAR CAST IRON FLAP GATES
: D
FIGURE 3.1.3.2
1" Grout pad
ftecomnwnded method* of Installation include mounting on cast-
Iron wall thimble (top) or mounting on concrete wall (bottom)
- Width -
Height
"E" thickness of mounting flange. Mounting flange drilled
for mount Ing on a wall thimble or directly to concrete.
TABLE OF DIMENSIONS (Inches)
Width x Height ABODE
12 X 12
18 X 18
24 X 24
30 X 30
36 X 24
36 X 36
36 X 48
36 x 54
42 X 42
48 X 18
48 X 24
48 X 30
48 X 36
48 X 48
48 X 60
54 X 54
60 x 36
60 X 48
60 X 60
60 X 72
72 x 48
72 x 60
72 X 72
84 x 84
9o X 96
19
25
32
38
45
45 '
45
46
51 Vi
56
5&
56
56
57'/2
57Vi
64
69'/2
69'/2
69'/2
69V»
81 Vi
83
83
95
107
19'/4
27
35V»
43
36
51
66%
72Vi
583/4
28
35Vi
43
51
66V.
81 3/4
74'/2
51 V«
663/4
81V*
95Vi
643/4
82'/2
95
-------
FIGURE 3.1.3.3
CIRCULAR PONTOON FLAP GATES
DIMENSIONS —INCHES
Sizt
Diarri.
48
54
60
66
72
78
84
SO
96
102
108
114
120
A
59Yj
66M
73
80
86^
93
992*
104
113J4
119%
126
132K
139
B
54
60
66
72
78
84
90
96
102
108
114
120
126
C
3T/4
40M
43J4
46J
-------
FIGURE 3.1.3.4
SQUARE AND RECTANGULAR PONTOON FLAP GATES
w. WIDTH of
DIMENSIONS —INCHES
CONSTRUCTION
1. - Flap—Stainless steel
2. - Frame-Cast iron
3. - Hinge link-Cast steel
4. - Hinge-Bronze
5. - Adjusting screw—Bronze
6. - Seat—Neoprene
7. - Lifting eye-Stainless steel
8. - Hinge post—Bronze
9. - Pins—Bronze
Size
Wdth. x Hgt.
48x48
54x54
60x60
66x66
72x72
78x78
84x84
30x90
96x96
102x102
108x108
114x114
120x120
A
57
63
69
75
81
87
93
99
105
111
117
123
129
B
54
60
66
72
78
84
90
96
102
108
114
120
126
C
37%
40J4
43J4
46%
49%
52%
55%
58%
6VA
64%
67%
70%
73%
0
48
54
60
66
72
78
84
90
96
102
108
114
120
These gates are also available in
rectangular types in any width and
height in 6" increments; for exam-
ple—60"x48"; 72"x96"; 108"xl20",
etc.
Dimensions are approximate.
Courtesy Caldwell-WUcox Co.
85
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FIGURE 3.1.3.5
SQUARE AND RECTANGULAR TIMBER FLAP GATES
D—I
TIMBER FLAP VALVE DIMENSIONS
Width x Height ABC D
36x48
36x60
48x48
48x60
60x36
60x48
60x60
72x48
72x60
72x72
84x48
84x60
84x72
84x84
96x48
96x60
96x72
108x36
108x48
108x60
120x72
120x84
46
46
58
58
70
70
70
82
82
82
94
94
94
94
106
106
118
118
118
118
130
130
58
70
58
70
46
58
70
58
70
82
58
70
82
94
58
70
82
46
58
70
82
94
13
13Vi
13'A
14'/4
14
14'/4
15V4
14V4
151/4
16
17V4
18'/4
19
19'/2
17V4
18'/4
19
19
19»/4
20'A
21
21 Vi
3J/4
33/4
4'/2
4
-------
ALLOWABLE WORKING STRESS (psi)
Timber
Compression
Yellow-Pine
Cypress
Douglas Fir
Greenheart
Tension
1550
1466
1100
3000
Parallel
to Grain
Shear
2000
1733
1450
3300
Compression
135
133
95
400
Perpendicular
to Grain
455
300
390
1500
Greenheart (Ocotea Rodioli) is used for the lock
gate sills in the Panama Canal. The gfeenheart is eaten
by the teredo and has an average life of 9 years
compared to 2 to 4 years for oak or pine. The high
temperature of the water is considered responsible for
its short life in Panama since there are records of its
use in England and Germany for periods up to 40
years.
Generally cast iron gates are used for smaller sizes
and pontoon or timber gates for the larger sizes. The
use of cast iron for large flaps makes the gate
difficult to handle and increases the differential head
under which the gate will open. For this reason New
York City limits the application of cast iron gates to
48 inches square.
The choice between timber and pontoon types
depends on several factors. In New York City, where
tidal waters are corrosive, the life span of pontoon
gates is 10 to 12 years compared to upwards of 30
years for timber gates. The pontoon gates have a
more stable shape than timber gates but eventual
corrosion of the plates causes the air cells to fill with
water and destroy the flap buoyance. One procedure
to prevent this is to fill the cells with a plastic such as
styrofoam. While timber gates have greater life they
are subject to warping and destruction by marine
borers.
Tide gates may be installed on concrete walls by
use of anchor bolts, cast iron pipe flanges or cast iron
wall thimbles embedded in the concrete wall. The use
of a wall thimble is preferable.
The gate is attached to the frame by at least two
hinge arms. Each arm should be provided with two
pivot points with lubrication fittings. Proper
maintenance requires periodic lubrication of these
fittings.
The seat between the flap and frame can be
either bronze or resilient material' such as neoprene or
Buta-N rubber. The use of a resilient material is
preferable to achieve water tightness.
The gate should be provided with a lifting eye on
the lower edge. It is desirable to provide a permanent
chain from the lifting eye to an accessible point so
that the flap can be opened when clogged, for
removal of debris.
Tide gates require periodic inspection during low
tides for cleaning and during high tides for
observation as to their water tightness.
3.2 Design
3.2.1 Guidelines
The addition of a tide gate, a regulator and the
required chambers at a sewer outfall increases the
head loss through the sewer and raises the backwater
effect in the sewer during periods of high stages in
receiving waters. This increase of backwater levels
may not be great enough to be of serious con'cern;
however, as a precaution, the possible change in the
hydraulic profile should be computed for anticipated
high water levels in the receiving waters.
Since the peak storm flow and the maximum tide
or stream elevation are both events of short duration,
the probability of the simultaneous occurrence of the
two events may not be very great and is outside the
scope of this Manual. The designer must use his
judgment in selecting the tide or stream high water
level for use in his computations.
The additional hydraulic losses resulting from
installation of the regulator and tide gate are due to:
(1) Loss through the tide gate; (2) losses in the
diversion chamber of the regulator; and (3) losses in
the tide gate chamber. It should ,be noted that the
friction head loss in the storm sewer downstream of
the regulator may decrease due to the lessened
discharge resulting from some flow diversion at the
regulator.
The discharge through the tide gate will be the
flow in the upstream sewer, less the flow diverted to
the interceptor. If the tide gate is placed at the end of
the storm sewer the flap usually will be the same size
as the sewer. If the gate is placed in a chamber it
87
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usually will be square 'Or rectangular in shape, with a
width equal to the diameter of the upstream sewer,
and a height somewhat greater than the water depth
upstream of the gate. The gate invert will be the same
elevation as the regulator diversion dam.
A typical plan of a regulator structure with a tide
gate chamber and the hydraulic profile through the
storm sewer and regulator is shown in Fig. 3.2.1.
Sample computations for the profile shown in Fig.
3.2.1 are given in the following paragraphs.
The sample computations are based on the data
used for design of cylinder-operated gates. In the
latter computations the water surface in the diversion
chamber was arbitrarily selected at elevation 21.00.
The computations which follow indicate that the
water surface should be at elevation 21.77 as a result
of additional hydraulic losses due to the tide gate
chamber. Therefore, in final design the computations
shown herein for the cylinder-operated gate should be
revised to reflect this higher water surface.
5.2.2 Design Formulas
The head loss through tide gates may be assumed
to be 0.2 feet, according to some gate manufacturers.
The design criterion of one city is to select a tide gate
with an area 10 to 15 percent greater than the area
of the combined sewer and to place the invert of the
gate not more than 0.5 feet above the invert of the
combined sewer. One city specifies that the head loss
through the gate shall not exceed 0.5 feet; another
city specifies a maximum of 0.33 feet. The relation
between tide gate head losses and conduit velocities is
presented in "Hydraulics Design Chart 340-1" in
"Hydraulic Design Criteria" by the U.S. Army
Engineers, Waterway Experiment Station, Vicksburg,
Mississippi. With respect to this chart the design
criteria state:
1. Flap gate head losses can be determined by
the equation: HL = KV2/2g
where
HL = head loss in ft. of water
K = head loss coefficient
V = conduit velocity in ft. per sec.
2. Hydraulic Design Chart 340-1 presents head
loss coefficients for submerged flap gates. The
data result from tests by Nagler6 on 18-and
30-inch diameter gates.
3. Modem tide gates are heavier but similar in
design to those tested by Nagler. It is suggested
that Chart 340-1 be used for design purposes for
submerged flow conditions until additional data
become available. Head loss coefficient data are
not available for free discharge.
The chart in Fig.3.2.2 relates head loss through
the gate to the velocity in the conduit. This chart is
based on circular gates attached to circular conduits
of the same size; hence the velocity in the conduit
and through the gate will be similar. In the case of the
regulators considered, in this Manual the velocity in
the upstream sewer and through the tide gate may
differ; therefore, in the sample computations herein,
the velocity through tide gate has been used .in
connection with Fig. 3.2.2.
Other hydraulic losses through the regulator are
computed from the applicable formulas outlined in
the subsection on cylinder-operated gates, in Section
2 of this manual of practice.
6 F. A. Nagler, "Hydraulic tests of Calco automatic
drainage gates," The Transit, State University of
Iowa, vol. 27 (February 1923).
88
-------
FIGURE 3.2.1
89
-------
FIGURE 3.2.2
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HEAD LOSS COEFFICIENTS
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wu •-•<>
Courtesy Waterways Experiment Station, Corp^ of Engineers
90
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3.3 Sample Computation
Flap Gate
Note: Use same data as for cylinder-operated gate.
Assume that design high water level in receiving stream is same as normal depth in combined
sewer for 10-year storm prior to construction of regulator. Determine effect of regulator on
water surface in combined sewer.
V = Velocity
Vt = upstream velocity
V2 = downstream velocity
d = depth of flow
D = diameter
g = acceleration of gravity
Data on combined sewer prior to
construction of regulator
At regulator
D = 5.0' s = 0.0022 Q = 120 cfs
d = 4.0' v(full) = 6.2fps
V = 7.0' V2/2g = 0.76
At outlet 100' from regulator
100x0.0022 = 0.22
.* Design high water level is
After construction of regulator
Diverted Q = 30 cfs
Q in storm sewer = 120 — 30 = 90
Storm sewer L = 100'
Downstream end
d (normal) = 3.20
d (actual) =4.00
9
» «
compute backwater effect
in storm sewer
V = 5.4 fpsV2/2g = 0.44
Compute backwater curve upstream by
standard-step method (see Table XVII,
ASCE Manual No. 37)
Upstream end
V = 5.5 fpsV2/2g = 0.47
ELEVATION
Invert HGL EL
17.00
21.00
21.76
16.78 20.78 21.54
20.78
16.78 20.78
21.22
17.00 20.80 21.27
91
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3.3. Flap Gate
Flap Gate Chamber
V = 90 = 2.5 _N/1 = 0.10
8 x 4.5 2g
(in chamber)
Entrance Loss
0.5 (V? - V|) = 0.5 (0.47 - 0.10) = .18
2g 2g
Neglect friction loss
Flap gate loss - use Figure 3.2.2
Use 60" x 60" gate
V - 90 = 4.5 fps
5.0 x4.0
V2/2g = 0.31
D_=.5JP_= 16
Hv .31
K = 0.7
HL = 0.7x0.32 = 0.21
21.56 + 0.21 =21.56
ELEVATION
Invert HGL EL
17.00 21.35 21.45
Upstream of flap gate
21.56 + 0.31
Diversion Chamber
V
90
.= 2.8 fps
8 x (21.5-17.5)
V2/2g = 0.12
Contraction loss
- 0.1 (V| -V? ) = 0.1 (0.31 - 0.12) = 0.62
2g 2g
Outlet loss = (V? -V|)
2g 2g
= 0.76-0.12 =0.64
Combined sewer
17.50 21.56
21.87
17.50 21.77 21.89
17.50 21.77 21.89
17.00 21.77 22.53
Therefore the installation of the regulator will raise the water surface of the combined
sewer upstream of the regulator during a 10-year frequency storm by 21.77 — 21.00 or 0.77 feet.
92
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SECTION 4
INSTRUMENTATION AND CONTROL OF REGULATOR FACILITIES
CONTENTS
Page
4.1 Elements of Instrumentation, Activation: General 95
4.2 Metering 98
4.3 Telemetering 99
4.4 Communications 101
4.5 Data Handling 102
4.6 Decision Making 103
4.7 Supervisory Control 104
4.8 Activation of Control Element 106
93
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4.1. Elements of Instrumentation
Activation: General
This section is directed principally at the more
recent techniques of control and instrumentation that
may be adaptable to the development of more
suitable means of regulation. It is prepared from the
viewpoint of the electrical and instrumentation
designer: the subject matter pertains specifically to.
equipment for:
1. Metering - means of measuring and sensing
system conditions;
2. Telemetering - means of transmitting data to
some data gathering points;
3. Communications - means of interconnection
from remote to data gathering point;
4. Data Handling - means of collection, display,
storage and manipulation of data;
5. Decision Making - means of translation of
data to control requirement;
6. Supervisory Control - means of dispatching
control to activation facilities; and
7. Activation of Control Element - means of
activating regulating device.
These concepts imply the establishment of a total
system control center at which point a complete
system of sewers and all its associated components
appurtenances may be under the direct supervision
and control of management. This will be a necessity
at some large jurisdictions and to a lesser degree at
smaller jurisdictional systems where only a few
manually supervised elements are used. The general
principles will be the same and installation in the
instrumentation-control field should embody the
concept of the ever-widening scope of which each
element may become a part.
The development of the regulation control center
must be a step-by-step undertaking, starting with the
gathering of data and implementing remote control
while gradually increasing the control center's data
handling capability with additional equipment.
Present regulator practice makes use of both
fixed and adjustable hydraulic devices such as: Dams,
horizontal orifices, vertical orifices, overflow weirs,
leaping weirs, adjustable gates; tipping gates, and
siphons.
The amount of flow in each case is seldom
measured, but by nature of the regulator design is
supposed to be within certain limits based upon
hydraulic calculations under assumed conditions such
as, for example, free discharge downstream. Two
major conditions arise, however, which make the
effectiveness of present regulation practices a
continuing problem. First, the desired orifice
becomes altered or gates malfunction because of
clogging and second, downstream channels may
become surcharged. Since there is usually no means
of indicating flow, there is no means of indicating the
degree of regulation which occurs.
In the case of fixed or static regulator stations,
nothing can be done to correct a control malfunction
except to remove the obstruction. Sensing of the
problem can be accomplished and communicated
with suitable identification to supervisory personnel
and conveyed to maintenance personnel for remedial
action.
Adjustable regulating stations can be monitored,
and gate openings can be remotely adjusted from a
central control, provided such facilities are made
available, to compensate for the changed conditions
affecting the station. If, for example, a partial
blockage restricted an orifice, the gate could be
opened wide to effectively change the port area to
allow the desired flow.
With regard to instrumentation and activation
facilities, instrumentation only applies to static
regulators. In this respect, monitoring devices with
suitable communication facilities can detect and
indicate the hydraulic conditions either in the vicinity
of the regulator or at some point on the system that
reflects the operating condition at the regulating
station.
Both instrumenation and activation facilities can
be used with automatic dynamic regulators. In this
application instruments can be used for sensing the
conditions and for handling information, whereas the
activation facilities may be employed to manipulate
the configuration of the regulating stations.
The concept of controlling an individual
regulating station is a simplification of the concept of
regulation as it applies to a complete waste water
system. Complete system regulation requires the
development of facilities and techniques to efficiently
route, limit divert, transfer, and "park" or store waste
waters.
Regulation of sewers, like any other control
system, can be broken down into the following
elements: Measurement; status determination;
information or data gathering; manipulation of data;
decision making; execution, verification, and
evaluation.
Measurement and status determination is effected
by sensors of various types developing electrical
signals to represent such objectives as flow, level,
head, differential pressures, gate positions, and
equipment status. Data gathering equipment is used
to condition or code electrical signals for transmission
95
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over usual communications channels. Equipment for
manipulation of data consists of indicators, recorders,
loggers, alarms, and computers. Decision making is
performed by supervisory personnel or by computer
programs. Execution is by dispatching service and
maintenance personnel, or by employment of
supervisory control equipment for remotely operating
the stations. Verification is carried out by updated
measurements and status indications. Evaluation is a
decision or judgment-making process, either manual
or automatic, to determine the results of the initial
execution of a control action. Repeated control
cycles are performed until satisfaction occurs.
The control equipment may take many forms.
Generally, sluice gates or shear gates will be.employed
to limit and re-route flows; whereas pumping
equipment may be used for transfer to and from
off-system storage or holding facilities. Pumps also
may be used for transfer within a system to take full
advantage of system capacities for storage. Not only
is it essential to manage storm water flows, but also
some treatment, chlorination for instance, may be
required. In such instances, the control equipment
will likely include remote dosage monitoring of
chlorinators with the rate of chlorine feed
automatically paced by the measured rate of storm
water flow. Additional sensors may be required for
determination of such situations as chlorine residual
and contact time before release from the system.
Usually, means to transfer flow has a variable
capacity in order to match the incoming flow.
Equipment used may include control and monitoring
facilities for variable speed pumping equipment.
An interesting example of regulated pumping is
the case where pumping from the downstream
terminal of an interceptor sewer is performed only at
a rate of flow necessary to .lower the hydraulic
gradient so that incoming flow to the interceptor can
be accepted, thus always pumping at the minimum
head necessary to match the incoming flow. Under
this condition the pump station wet well is at
minimum level at maximum flow or maximum level
at low flow or low pumping rates. Moreover, the
capacity of the interceptor is used to its maximum
capability for storage. Such a scheme becomes quite
complex and requires programmed control which
may either be built into the control equipment or be
effected by computer.
Although the treatment of sewage falls outside
the scope of regulation, those who manage the
regulation of a complete system must be concerned
with the operating capacities of plants and with
outfall sewer conditions. Thus, plant flows and
receiving body water levels are pertinent data
required at the regulator control center. Additional
stream monitoring data pertaining to water quality
also might be transmitted to the control center for
overall guidance and record purposes. Additional data
such as weather reports from the Weather Bureau and
rain gauge data telemetered to the control center
should assist management to effect adequate controls
when a storm impends.
Successful development of means to effectively
regulate complex sewerage systems, either combined
sanitary and storm wastes or separated wastes,
requires a management information and control
system. In spite of the interest that exists, as is
evident from the number of articles, and discussions
on the subject, few such information systems actually
have been implemented. One reason for this has been
cost. Another reason is that there is neither a
well-defined perception of the range and extent of
the. information and control requirements nor tried
and proved methodology for its implementation. The
traditional justification for information systems,
monitoring of sewer levels for example, has been
based to a great extent only on reduction of
operating costs. Justification for an information
system, in the future, should be based on the net
worth of the information. The net worth may be
defined as the difference between the value of the
information obtained and the cost of obtaining this
information. Traditionally, the instrument and
control designers determine the cost; Management
must determine its value.
Information is even more valuable when it flows
to and from management, allowing decision-making
and execution, and thus more responsive control.
From an instrument and control standpoint, a sewer
monitoring system is an example of information
flowing only one way—to management. By
implementing supervisory control equipment for
remote control, the value of the information is
greatly increased if it allows management to exercise
real time control. Real time control is the ability of
management to detect and correct a deviation from
plan or standard before the deviation becomes so
great that it is not possible to return to the original
plan or standard. It is not necessarily instantaneous or
even fast control, since the speed of response required
for a real time control depends upon the nature of
the activity being controlled. For waste water systems
control the speed of response usually may be in
minutes and hours.
The constraining factors in the development of
information and control systems are control facilities,
96
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communications, power, and site preparation. None
of these except hardware is necessarily difficult and
needs no particular discussion in this manual. Very
little has been accomplished, however, in the design
and development of suitable hardware for sensing the
rate of flow. In this respect, and at the present stage
in the art of instrumentation, it should be recognized
that immediate values of velocities and levels are of
more value than totalized quantities of waste water.
Determining the specific information and control
requirements is probably the most critical part in the
design of any information and control system. These
needs also must be taken into account in the future
design of sewer systems. The cost to harness a
regulating station with monitoring devices and remote
control has little relationship to the size of the
station. In future designs it may be prudent to
employ only a few large regulating stations rather
than a large number of smaller ones. It will also be
important to locate regulators where they can be
conveniently attended and serviced.
Information and control systems offer
tremendous benefits to the water pollution control
agencies and represent practically a new frontier for
instrumentation and data handling. Examples of
beneficial regulating practices are many.
In one jurisdiction where storm water overflow
or diversion occurs the major purpose is to avoid
hydraulic overload of treatment works in addition to
avoiding flooding of local areas. Overflow chambers
are metered and other overflows are. electrically
controlled and telemetered to the plants for their
operation. The control center is located in a main
office building to which data are transmitted
concerning rainfall incidence and waterway
elevations. The engineer of waterway control provides
information to the engineers of treatment plant
operation who decide the course of action.
To achieve the objective of using available storage
within the existing combined sewers for regulating
storm w,ater flows, the jurisdiction installed -a
"Computer Augmented Treatment and Disposal
System." Reduction of sewage overflow frequency
and magnitude also is part of its objective. When
overflows cannot be avoided, the system controls
discharges at selected stations to minimize harmful
effects on marine life or public beaches. Storage
control is effected through remote electric control
and local automatic controls of the pneumatic type.
These local control units come into use only when
the remote control equipment fails. Gates at each
outfall are remotely controlled by electronic .
circuitry. Remote control of-the datum level chosen
at each location is carried out by transmission of an
operation command signal to the remote terminal
equipment. When the desired datum has been
reached, a command signal is transmitted to the
remote terminal to deactivate the equipment. When
the remote control units fail, local automatic control
is restored. The control center is outfitted with an
operator's console and wall map which relate to the
system. Data are telemetered to a central location
over leased telephone lines and the information is
entered in a process control computer which also
directs data gathering.
At another jurisdiction, it has been found -that
about 80 percent of the annual overflow volume is
discharged from 20 overflow structures.
Consideration is being given to the elimination of all
overflows in'some areas. This would be accomplished
by bringing all combined sewers to a central gate
chamber where the gates would be power-operated
and remotely controlled by means of a telemetering
and supervisory control system. The chamber would
be operated as a single overflow during periods of wet
weather. Control of the overflow would be
accomplished by a central operator who would have
telemetered data concerning waste water flows at
treatment facilities, the water level and available
storage capacity in the intercepting sewers and the
water level at critical points in the system and at the
gate chambers. Thus the operator at the control
center could affect the flow throughout the system.
Use would be made of the monitoring and
telemetering system in the operation and control of
the system, in particular for surveillance of the pump
stations for malfunctions, failures, and other system
problems.
The benefits of flow control in combined sewers
at one sanitary district appear to warrant a significant
expenditure for equipment. Flow in the sewer system
was studied, using pneumatic depth of flow recorders
placed at key positions. Purpose of the gauging was to
determine the extent of system loading, in addition
to gathering other data. In 1960 it was found that a
volume equal to 10 mgd in the joint interceptor sewer
required an expenditure of $600,000 based on
dry-weather flow. This means that every 10 mgd of
storm water removed from the joint interceptor had
an equivalent worth of $600,000 of sewer capacity.
This concept of providing capacity for sanitary flows
led to consideration of using powered regulators and
a system of controls for removing flow from, or
permitting flow to remain within the interceptor
system. Effective control of the regulators was seen as
a measure for reducing the overall quantity of raw
97
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sewage diverted to receiving waters during rainfall
periods. The system being considered included an
integrated system of regulator operations with
supervisory control of key regulators. The regulator
operation would be based upon interceptor usage.
Power-operated gates controlled by a supervisory
system from a control center would use telemetering
to provide information concerning the gate positions,
flows, and flow levels in the interceptor sewers. Data
collected would inform the operator of the system
the situation and permit system adjustments. The
operator would have the choice of bypassing flow
quantities at certain locations. Evaluation of the
receiving water conditions at various locations would
be made by the operator who would make required
adjustments. Automatic readout of data for analysis
and use of manual or computer techniques are
visualized.
Still another example of the requirements of
monitoring and supervisory control is the situation in
another sewer district where a second conduit will be
installed to parallel an existing relief sewer. In this
case, it will be necessary to retain peak flows in one
of the two conduits until a quantity is reached where
it is possible to divide the flow between the two
sewers and still maintain adequate velocities in both.
Obviously, some form of level and velocity
monitoring and power-operated gates are likely
solutions.
4.2 Metering
Regulation, herein is defined as the control of
waste water flow. Control implies exercising direction
over the amount, the rate of flow, and the routing of
the flow. Effective regulation therefore must be
accompanied by some means of measurement.
Important characteristics of waste water flow
are: (1) Conduits usually are only partially filled; (2)
substantial amounts of debris are carried"; (3) flow is
not under pressure other than gravity; and (4)
conduits frequently are located at considerable
depths below grade.
Conventional measuring devices used on water
distribution systems are not practical for measuring
waste water flow. Open channel flow metering
structures can be employed with some degree of
success but they are accompanied by additional
problems peculiar to the waste water system. Such
structures can become • very large and expensive and
are most appropriately placed near the surface where
they are more accessible. Open channel meters are
not only directional, but also become inoperative
whenever they become submerged.
Always a problem of using an open channel
metering structure is the measurement of water level.
Most of the open channel flowmeters are designed
with the intent of using floats for measuring levels.
The use of floats in waste water metering practices
only can be practical for temporary meters or those
which will be installed within stilling wells and
continuously purged with clear water, or those which
can be continually supervised and maintained. The
use of bubbler systems for measurement of
differential levels across Parshall flumes has been
employed with greater success. Bubbler systems for
direct level measurements provide some advantages
over floats.
None of the conventional flow measuring devices
is designed for the express purpose of waste water
measurement and all presently in use are designed for
a much narrower range and higher accuracy than
would be required for the monitoring of waste water
flow. Therefore, the practice of regulation can not be
expected to be any more successful than the available
means for sensing flow.
Successful regulation practices will depend on the
development of new methods, principles, and designs
of flow measuring devices adaptable specifically to
sewers and waste water characteristics and
environments. Unfortunately, the present state of the
art of waste water flow metering is seriously behind
most other metering accomplishments.
Managers of sewer systems must make known
these requirements to research, development, and
manufacturing organizations. Rather than
concentrating on the development of flowmeters, for
example, it might be wise to explore the development
of a pair of sensors, one to determine level and the
other velocity. Then with level and velocity as basic
data, the flow could be computed by taking into
account- the conduit configuration. Immediate
velocity and level measurements would provide
management with a better description of the
conditions taking place at some point in a conduit
than would a flow measurement, and each possibly
could be more accurate than some emperical
determination reflecting the combination of the two.
Another concept that might be explored is that
of sampling for level and velocity measurements.
Such an approach might lend itself to the possibility
of employing retractable devices or probes for these
purposes so that fixed obstructions would not impede
the normal transport of solids and debris. Retractable
probes could continually sense level and velocity,
interrupted occasionally for retraction, so that any
debris held by the probes could float on downsfream.
The probe could not only be level and velocity
98
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sensitive, but could also be bi-directional, sensing
velocity in either direction. Such a probe should be
sufficiently strong to withstand the impact of heavy
floatables and be constructed of corrosion-resistant
materials. Probes of this type are patented and are
presently being considered for development by
several instrument suppliers. It may be wise to ease
the requirements for accuracy and sensitivity
normally expected for metering and settle for greater
durability and simplicity of equipment.
Other new developments in the field of
measuring liquid velocity and volume flow rates make
use of sonar principles to determine transient travel
of an acoustic pulse between submerged probes. The
meter probe provides an unobstructed flow path
without head loss. This equipment is represented to
measure flows from 0.02 ft:/sec. to 300 ft./sec.
continuously and to have successfully measured flow
in a 24-foot-diameter conduit at no more than one
percent error.
A relatively new device which is convenient for
use in measuring liquid level is the controlled leak,—a
precision, porous-metal • gas flow restricter. This
device can be used to bleed gas such as nitrogen from
a bottle, at a rate of less than one bubble per second.
The back pressure on a pipe bleeding the gas into a
fluid bears a direct relationship to the length of the
submerged portion of pipe. For measuring liquid
level, this allows the use of a nitrogen bottle and
controlled leak to replace the usual installation of an
air compressor and differential regulator and the
accompanying appurtenances normally required for a
bubbler system. Such a system can last for many
months without refilling a standard size gas bottle.
Solid state pressure, level, and flow transmitters
are being developed for telemetering which can be
powered over a standard telephone line, thus
eliminating the requirement for power at the
transmitter site.
4.3 Telemetering
4.3.1 General
Telemetering is a means of Conversion of a
measured variable or sensed condition into a
representative electrical signal, the transmission of
that signal, and its reconversion to a suitable
quantitative form which may be displayed, indicated,
recorded, logged, or stored and utilized to compute
or control.
The selection of the type of telemetering
equipment to insure its maximum effectiveness for a
particular application requires not only a careful
evaluation of the many types available, but more
significantly of the design criteria which may be
imposed by the particular purpose for which it is
applied.
For regulation practices, certain design, criteria
are dictated by the characteristics of a sewer system.
Such design criteria are:
1. Wide coverage—data are required from all
over the system and its environs;
2. Relatively small amounts of data—only a
comparatively few and in some cases only one
point of data is required from each site;
3. Unattended sites—data measurement are
frequently required at unattended sites;
4. Uncontrolled environment —data
measurement are generally at site of uncontrolled
environment; and
5. Alterable and expandable—points of data
requirement occur gradually and in small
increments, only to keep pace with sewerage
system expansions.
From the above, it readily can be determined
that certain features of the outlying station
telemetering equipment are particularly desirable,
such as:
1. Inexpensive;
2. Infrequent service requirement—not more
than quarterly or semi-annually;
3. Applicability for wet and corrosive
environment;
4. Applicability for unregulated, normal power
supply;
5: • Applicability for ordinary two-wire
telephone;
6. No distance limitations; and
7. Adaptability to grouping of a number of data
signals on one communications channel.
Of the many major types of telemetering
equipment available, some of the most commonly
employed with respect to their transmitted signals are
as follows:
4.3.2 Current Type
The output signal is a variable electric current.
This type requires a continuous two-wire,
fully-metallic individual circuit and is quite limited in
distance. It is most suitable for in-plant and on-site
telemetering, particularly where electronic
instrumentation is involved.
4.3.3 Voltage Type
The output signal is a variable voltage. This type
requires a continuous, two-wire fully metallic
individual circuit, is limited in distance, and is quite
subject to induced interference. In many instances
this type requires a shielded circuit.
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4.3.4 Frequency Type
The output signal is a variable frequency. This
type requires two-wire circuit or the equivalent. It has
no distance limitations and is suitable for high speed
data transmission. It has not experienced widespread
use for water or waste water signaling, perhaps
because it generally has been more expensive and
more of a proprietary item than other types available.
4.3.5 Pulse Count Type
The output signal is a variable rate of operation
of a contact-making device. This type is a simple,
inexpensive electro-mechanical system. It requires
only a two-wire circuit or the equivalent and has no
distance limitations. Primarily, it is used for dynamic
variables such as flow' or running counters, and
generally is not adapted to more static variables such
as pressure, level, or position.
4.3.6 Pulse Duration
The output signal is a variable duration of the
closure period of a contract-making- device being
operated at a constant rate. This type is frequently
called time-impulse. Usually it is a simple,
inexpensive, electro-mechanical system, utilizing any
two-wire circuit or the equivalent. It has no distance
limitations and commonly has' been used for water
and waste water signaling of such variables as flows,
pressures, levels, and positions.
4.3.7 Digital
The output signal is a coded pulse train. This
type of equipment generally is more sophisticated
an3 expensive; however, its signal format is
particularly suitable for automatic data logging and
data handling. It has very high accuracy and speed
transmission, operating over a two-wire circuit or the
equivalent without distance limitations. It is the
newest in the art of telemetering," although not yet
developed to the stage where transmitters specifically
designed for waste water measurements are yet
available.
4.3.8 Commentary Concerning- Telemetering
Equipment
In addition to taking into consideration the
characteristics of an overall system, the desired
features of the particular application, and the most
appropriate transmission signal, it generally has been
necessary to choose and specify equipment for which
there are competitive suppliers. Since pulse duration
type of telemetering is furnished by a number of
manufacturers and also meets the normal
requirements, it is perhaps the best known and most
widely used system for control of combined sewer
flows. Presently, governmental jurisdictions
successfully utilize a large number of pulse duration
type telemeters. In such cases it might not be prudent
to change unless there is sufficient justification,
Advantages of the other types, however, should not
be overlooked.
Presently, telemetering consists of remote
transmitters and indicating or recording receivers
located at pumping stations and treatment plants, or
central operations control centers. No automatic data
handling other than the pointer or pen positioning on
the receiver is usually involved. If additional handling
of the data is required, however, other considerations
are necessary. For example, a time-impulse signal
cannot be adapted for automatic logging. So the
various types of telemetering devices should be
reviewed with the prospect of automatic data logging
in mind.
Automatic data logging and computer data
handling require that the data signal be in digital
form. It would seem that digital telemetering would
be a more suitable choice of equipment.
Unfortunately, at this time' no primary metering
equipment for waste water type measurements has a
direct coded digital output. To obtain a digital output
signal, it is necessary to employ a conventional
primary meter with a current or voltage output, (an
electrical analog output), then to use an
analog-to-digital converter to obtain a digital output
for transmission to the control center. Such a scheme
requires expensive and elaborate facilities at outlying
stations. This is contrary to the design criteria, and
rules out the use of digital telemetering as a suitable
means for wide area gathering of flow, level, pressure,
and position data. This is not to say that its use will
not be common when more practical digital
transmitters are developed. Nor should this be
interpreted to apply in other circumstances where a
block of digital information is available at a site with
suitable environment for transmission to another
suitable location. It could be concluded that digital
.telemetering at least, would not be considered as a
substitute or replacement for the time-impulse type.
Frequency-type telemetering is suitable as a
substitute for pulse duration telemetering. However,
because it is not available from as many sources as the
pulse duration types, there is no particular price
advantage, and because many jurisdictions have a
large amount of pulse duration equipment in service,
a case for its specific use would not seem arguable.
Pulse-count-type telemetering, from an electrical
standpoint, also is suitable from the standpoint of
design criteria. Its application' is generally limited,
however, to displacement flowmeters or counting
systems which require a rotating body in the stream;
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hence it is not suitable for waste water applications.
Moreover, it is not as readily adaptable to time
division or tone-type multiplexing which, are simply
techniques for grouping a number of transmitted
signals on one communications circuit. Usually where
a number of analog data functions are involved, the
pulse count code would be converted to one of the
other forms of telemetering for multiplexing.
Voltage-type telemetering only should be
considered for on-site applications because of its
distance limitations. It does have the advantage of
having the data measurement in an electrical analog
form which lends itself to direct analog-to-digital
conversion.
Current-type telemetering should be considered
only for on-site applications because of its distance
limitations. It has the advantage of having a data
signal of an electrical analog form suitable for direct
analog-fo-digital conversion. Furthermore, it is not so
susceptible to electrical interference and usually
would not .require a shielded cable for its transmission
circuit. Consideration should be given to the use of
current-type telemetering for on-site applications.
Not only is it adaptable to digital data, it has
immunity to interference. The inherent requirement
of only a simple ammeter for an indicating
instrument make it desirable for compact panel
arrangement. The present trend in electric or
electronic instrumentation is toward the current and
voltage types. The current type is most frequently
used. Wherever the measurement data are required in
digital form, it is first'necessary to obtain it in either
its current or voltage analog. For the accumulation
and conversion of much data to digital form at any
on location, current-type metering is quite
appropriate.
Pulse duration telemetering holds a somewhat
unique position for water and waste water
measurement. Certainly none of the digital
equipment presently available can supplant its
existing utilization in water and waste water facilities.
Most types of chemical feeders as standard equipment
are presently designed to take pulse duration signals.
Many pump controllers and most analog
instrumentation are designed for use with pulse
duration equipment. Not until the requirement for
data in a digital form arises is the use of pulse
duration telemetering seriously questioned.
Perhaps the most straight-forward means for
converting pulse duration to digital form is the
employment of a standard re-transmitting
slide:wire-type potentiometer in a pulse duration
receiver. Voltage or current in the potentiometer
circuit could then be converted to a digital signal
proportional to the position of the slide-wire. The use
of a slide-wire, however, introduces another
component requiring service and replacement.
Therefore, it is desirable to obtain' a current or
voltage signal conversion from pulse duration without
the requirement of a slide-wire.
Another possibility of converting the pulse
duration signal to digital form is the employment of a
shaft position to digital encoder in a pulse duration
receiver. Although this is not available with present
standard receiving equipment the possibilities of this
concept should be more thoroughly investigated
before commitment is made to acquire digital
conversion equipment.
4.4 Communications
4.4.1 Communications Facilities
The most common communication link for
telemetering and supervisory control in the waste
water field is the leased telephone line. The
monitoring of regulation practices, like that of
monitoring in most other related industries, has used
leased telephone lines for both their existing
telemetering, circuits and their supervisory control
circuits. Generally, most experiences with the leased
lines have been reasonably successful, particularly in
cases where the importance of the communications
link has been sufficiently impressed upon the
telephone utility. Another means of communications
which could be employed would be by microwave.
4.4.2 Microwave Facilities
Microwave, a form of directional—point-to-
point-communication's utilizing ultra high frequency
equipment, provides a very large communications
signal capacity. Usually, there is not a sufficient
quantity of data signals at any given station on a
waste system to justify the choice of microwave on
that basis alone. Generally it is justified on
point-to-point applications where the distances are
quite great, and it is found that leased telephone
service either is not available or that the service
simply is unsatisfactory. Microwave equipment must
be operated on a line-of-sight basis from transmitter
to receiver, with intermediate repeater stations as
required by the nature of the terrain. Generally,
microwave is too expensive. for the wide coverage
necessary for control and supervision of the many
remote stations which may make up a waste water
system.
In cases where it is necessary to lease
communications links from several intermediate
telephone companies to form a complete circuit, it
may be necessary to employ microwave equipment.
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Microwave equipment is available from a number of
suppliers, is reliable and flexible, but requires
maintenance by an organizations's own personnel or
by the service contract.
4.4.3 Telephone Lines
Leased telephone lines, as normally furnished by
a telephone company, fall into three principal
classifications. Other classifications have been
recently established for very high speed data
transmission. These classifications may vary in quality
and performance from one place to another and
between companies.
1. Class 1, or Class C-is a direct current slow
speed telegraph circuit. Pulsing speeds are limited
to 15 cycles per second. These circuits are
generally continuous metallic with ground return.
Such circuits are quite suitable for single pulse
duration telemetering or individual control
circuits and presently are used under appropriate
conditions by many municipalities.
2. Class 2, or Class B-is also a direct current
(DC) or low frequency (AC) teletypewriter or
teleprinter circuit. Pulsing speeds are limited to a
range generally of 60 to 100 pulses or cycles per
second. Frequently, the Class 1 and Class 2
circuits are no.t available in residential areas. No
particular need for this class of circuit is foreseen.
3. Class 3, or Class A-is a voice grade circuit.
Generally, this class circuit may pass audio
frequency (AC) signals up to 3000 cycles per
second on short distance lines. Longer lines using
repeaters usually pass audio tones from 300 to
3000 cycles per second. This type of line is most
suitable for normal requirements in the subject
field.
4. Although not normally required, other
special classes used for high speed data
transmission have been developed and can be
furnished under special arrangements. Prior to
consideration being given to the actual acquiring
of any high capacity, high speed data handling
equipment, the telephone company should be
contacted regarding the type of equipment, the
nature and characteristics of their
communications circuits, availability, and cost.
4.5. Data Handling
4.5.1 General
Data is information that can be expressed
symbolically-measurements, time, equipment status,
identification, etc. Indicating and recording
instruments, alarms, mimic busses, and lights all have
been used for data handling. Data use will become
more complicated as it is used with regulation control
practices and techniques. At some point, automatic
handling of data will become necessary. The system
designer then must consider the use of computers for
logging and control.
Data logging has generally been the first step
toward data handling beyond the usual display of
data on indicator scales or recorder charts, or lamp
indications. The first models of data loggers usually
used some means of receiver self-balancing
potentiometer to position a shaft upon which a shaft
position encoder was mounted to digitize the output
of the receiver. Various inputs were switched to the
receiver encoder combination by telephone-type
stepping switches. The output of the encoder was
then fed to an electric typewriter. With the exception
of the encoder, the components—receivers, stepping
switches, and electric typewriters-generally had been
in use. Applications of such equipment have proved
quite successful in logging a great amount of data in a
short period of time, and where there was adequate
time between uses for service and maintenance.
Utilities requiring trouble free, day-in, day-out
logging service, however, found such equipment to be
in frequent need of service and repair. These
electro-mechanical-type data loggers are not
recommended for the continuous service required for
waste water regulating practices.
A second generation of data loggers has been
developed, using solid state voltage or current
generators in place of the self-balancing
potentiometers, digital voltmeters to digitize in place
of shaft position encoders, and reed or mercury relay
type scanning programmers in place of stepping
switches. Such instruments greatly reduced some of
the problems encountered with the earlier loggers and
permit higher speed and more flexibility in setting
alarm points or set-point control.
Either first or second generation loggers are
basically prewired systems. The second is easier to
modify because of its use of pin boards for
convenient changing of alarm, span, and zero
suppression settings. In either case the output of the
logger is basically a fixed log only, with no
convenient means of data manipulation such as might
be required if the data are to be used in conjunction
with a computer for trend alarms, computational
analysis, averaging, or other programmed
requirements.
The most recent data logger is the general
purpose, stored-program digital computer which is
used as the central data processor of a modern data
handling system. Once the digital computer is put
into the system, it will do the jobs which were
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difficult or impossible to do with the original logger.
It will also do anything the second generation loggers
could do, and store data, permitting the data to be
used in whatever manner a programmer may call for,
including closed loop computer control.
4.5.2 Digital Computer Capacity
The data handling digital computer can have the
following capabilities:
1. Computer memory can store alarm settings,
and zero and suppression settings, -thus
eliminating fixed wire pin boards or separate
instrument alarm contacts.
2. Subroutine programs can eliminate the clock
and calender required in the earlier type loggers.
3. Computer can remember alarm points during
the last scan and initiate and display programmed
instructions when an alarm is found.
4. Linearizing of signals can be done by
computer programming.
5. Pulse inputs can be counted directly by the
computer, eliminating the individual pulse
counters.
6. Time duration inputs can be read directly by
the computer by means of program interruptions.
7. Analog-to-digital converters can become a
part of the computer.
8. The computer can measure zero drift on low
level signals and compensate for it.
9. The computer can sense an excessive rate of
change of variable, to give trend alarms prior to
reaching the point of alarm condition.
10. Simple to complex computations can be
performed on the data received.
11. Memory of the computer permits an
operator to recall data prior to an alarm for
examination. For example, in the event of an
alarm, the data handling system can
automatically or on demand print out the values
of significant variables for say every ten seconds
of the five minutes preceding and following the
time of alarm.
12. A trend recorder can plot data from storage.
For example, in only a few seconds a 24-hour
recording of an input such as a flow, pressure, or
temperature can be made by simply selecting the
variable to be analyzed.
13. The computer can accept new commands
from the operator.
14. The complete logging program may be
revised or modified without making any external
changes.
15. The digital computer-type data handling
system can be adapted to closed loop computer
control.
The greatest advantage of the digital computer
logger is that once it is put into the system, it can be
programmed to do additional work unforseen at the
time . of its original installation, at almost no
additional cost.
The data handling facilities must have the
capacity for handling a vast amount of data, yet be
capable of discriminating between that which is
normal and that which must be called to an
operator's attention. Data requirements for the future
can not be determined with accuracy. Thus a
hard-wired electro-mechanical logging system should
not be purchased. Hard-wired systems become more
and more complex and inflexible as the number of
points of data increase. The computer-type logger, on
the other hand, can originally be purchased with a
great amount of data handling capability with
characteristics and execution methods to be changed
as the input data amount increases.
Concentration of effort on the acquisition and
accumulation of suitable data must precede
installation of a system.
4.6. Decision Making
When measuring devices, telemetering,
communications, data handling, supervisory control
and outlying station activation facilities have been
acquired, only the decision and execution need be
performed .to close the regulating control loop. How
well the system is regulated then becomes a matter of
interpreting the data and judging tiie amount of
control to be executed. Deciding what to do may be
an extremely flexible arrangement wherein the
operations control center operator or attendant uses
his best judgment: Or it may be a fixed and inflexible
arrangement determined ahead of time and
incorporated in a programmed operation
automatically performed by the data handling
equipment or computer. Arguments can be made for
both arrangements.
A capable attendant can permit a wide range of
allowable conditions under various circumstances, not
necessarily defined by only the measured inputs;
whereas, with the computer, more nearly identical
controlled conditions can be depended upon during
similar situations. .
Closing the control loop manually is known as
off-line control. Closing the control loop
automatically is known as on-line and real-time
control.
A system which includes data logging, data
handling and supervisory control equipment of the
recent and more sophisticated types, can, with slight
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modification function with some on-line control. Any
system with the capabilities of on-line control must
be capable of switching to off-line control when
desired.
4.7 Supervisory Control
4.7.1 General
For management to exercise fullest authority
over the regulating control facilities, it is desirable to
have information regarding the effectiveness of a
regulator, and means to override or put into effect
additional controls. Control is a result of some
decision-making process and may be performed
manually or automatically.
Supervisory control equipment consists of three
basic elements: (1) The dispatcher's equipment; (2)
the means of communication; and (3) outlying
station equipment. Systems will vary from the
simplest-a control switch, directly connected to a
regulating gate operator—to a sophisticated regulating
system operated by a computer on closed loop
control. The methods and techniques used to
transmit information are similar to those used for
remote control. A computer handles not only data,
but also generates control output, either manually or
automatically initiated. It is necessary to recognize
the essential differences between conventional
supervisory and computer control. Because
supervisory control and computer control are such
broad, generic terms these are defined for the purpose
of this Manual.
Conventional Supervisory Control
A custom-designed group of selector switches,
push-buttons, indicators and electronic circuits
connected by a wiring harness and packaged in
completely integrated assemblies for installation at
the central and remote stations. These stations are
specifically designed and wired for the specific
application. The operation and performance is fixed
by the wiring, which has led to the use of the term
"hardwired" control.
Computer Control
A digital computer with standard logic, memory,
and wiring, installed at a central station. The
customizing for a particular application is done by a
list of instructions and programming, which are
magnetically stored in the machine. This electronics
programming gives rise to the term "softwired" type
for its particular application.
Either of these two classes of electronic control
systems allows the operation of remote equipment
from the point of central control. The central station
may have the data logging, data display and other
data handling options. Both require essentially the
same communication means. An operator at a control
center could not generally tell whether controls are
handled by a softwired- computer or a hardwired
conventional supervisory control system. There are a
number of ways in which these two classes of
equipment may be implemented. Four general
techniques to consider are:
1. Conventional Supervisory;
2. Computer On-Line Control;
3. Conventional Supervisory with Off-Line
Computer Monitoring; and
4. Computer On-Line with Conventional
Supervisory Standby.
Hardwired conventional supervisory control
equipment is a type that many operators have used
for years. It has the advantage of having a low initial
cost and central control may be implemented in
step-by-step stages of development.
Softwired digital computer control can not only
take over and perform all of the functions, but can
also accomplish additional tasks beyond the ability of
the conventional supervisory control.
The digital computer has no prewired control
capability. Therefore a program must be written to
customize the computer to a particular application
before it is used in a control system. Programming the
computer for control of remote stations requires
special skills. A combination of waste water practice
experience and computer application technique is
required. Conceivably, the programming expense
could exceed the cost of the conventional supervisory
control system.
The value of the computer system lies in the
additional benefits that fall into two general areas:
(1) The flexibility of modifying and expanding the
control system; and (2) the capability for data
processing.
The value to the waste water management of the
flexibility of modification and system expansion
alone are not of sufficient importance to influence
the selection of a computer. The control system for
any specific remote station will normally remain
static and unchanged after the initial requirements
have been determined and successfully established,
except for remote station expansion which could
generally be taken into consideration during the
initial implementation of the equipment.
4.7.2 Advantages of Data Processing
The capability for data processing, can be a most
important benefit. These benefits alone may justify
the higher cost and problems of program writing.
Some of the benefits to be realized by data processing
could be as follows:
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1. Programmed data logging at periodic
intervals;
2. Selective data logging, for example high
repetition log on a particular variable for
engineering study;
3. Computation and logging of quantities for
selected time intervals;
4. Computation and logging of the summation
of flows;
5. Computation and logging of inventory
storage facilities;
6. Rate of change alarms on flows, levels,
pressures, etc;
7. Deviation checking for off-normal conditions
with alarms;
8. Computation and logging of equipment,
operative status and running time;
9. Programmed or selected display of variables;
10. Programmed printout of instructions to
operators;
11. Computation of load and system studies;
12. Storage of information and computation for
billing purposes; ,
13. Preparation of data for storage in the form of
punched card, punched paper tape, or magnetic
tape;
14. Economic computations for operation
guidance; and
15. Capability of actually performing as an
element of the control scheme; that is, closing a
control loop by performing its own control
action.
Although the initial programming may be a
relatively costly item, it should be a non-recurrent
expense, and updating and changing to conform with
system growth or altered data manipulation should be
accomplished inexpensively.
4.7.3 Disadvantages of Data Processing
The disadvantages of each system are:
1. The conventional supervisory equipment:
a. Must be customized for each particular
application;
b. Requires rewiring to change control
patterns;
c. Has limited capability of data handling;
d. Lacks flexibility; and
e. Maintenance costs may be high due to
large number of components.
2. The digital computer control equipment:
a. Costs more initially;
b. Requires costly programming;
c. Compounds the maintenance and service
problem by requiring technical know-how in
two additional technologies, one, the
electronics of the computer and another,
programming techniques, in: addition to the
electronics of the fixed wired conventional
systems used at the remote stations.
4.7.4 Combining the Advantages of Supervisory
Control and Digital Computer Control
In comparing the two techniques, the
conventional supervisory control and the digital
computer control, it is easily concluded that there
would be considerable merit in initiating a
construction program in which the advantages of
both could be realized. This necessitates the use of
both classes of equipment in either of two
arrangements:
1. The conventional hardwired supervisory for
remote control supplemented with a computer
for monitoring and data handling;
2. The computer for on-line control and data
handling, supplemented with the conventional
supervisory equipment as standby for,use when
the computer is in down-time.
This second arrangement could be an outgrowth
of a successful experience with the first. In this
approach the hardwired conventional supervisory
control would be purchased and installed in
increments amenable to any overall program for
converting the outlying station' from manned to
unmanned remotely controlled facilities. As the
control system is expanded so are the computer
facilities for monitoring and data handling, together
or separately as the conditions and circumstances
govern.
Advantages of the on-line availability, of the
supervisory system, together with the data handling
capability of the computer, may then be realized in a
gradual manner without an initial full commitment to
either. This arrangement also has the advantage of
allowing the computer to be taken off-line for
program maintenance, problem solving or other uses
for which the computer can be applied without
disrupting the control of the remote stations.
The operations control center attendant would
initially generate all control function messages to
remote stations by manipulation of switches or
push-buttons at his dispatcher's panel or console. The
computer could monitor all messages going out to
remote stations and all remote equipment status and
remove measurement data being received from
remote stations. The computer could therefore
"listen-in" and be instructed to interrogate, check for
limits and off-normal conditions, process and log the
measurement data and cause whatever printouts
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including alarming and instructions the programming
diagnostics would provide. Ultimately the computer
might be programmed and interfaced with the
supervisory equipment to exercise a certain amount
of logical and routine control. This latter degree of
sophistication would be approaching the case of
computer on-line control with the manual supervisory
as standby.
For the management of sewerage systems, it
seems appropriate to place emphasis upon the
long-range establishment of an operations control
center. The plan of development should not require,
however, the initial investment for the procurement
of supervisory or data handling capacity for functions
that are not expected to be required for several years
nor for those partially known or unknown
requirements of the future.
System growth should not be projected too far
into the future. Changes, not only in the design and
technique of control and data handling but also of
the system affect future requirements. Rather than
forecasting and perhaps freezing the requirements, it
is better to arrange for considerable flexibility and
the possibility of gradual expansion.
Consoles and panels, for expample, should be
procured for only those control and metering
functions initially required without panel cutouts or
blanked panel space for the indefinite future. Console
and panel arrangements should be such that
additional sections or modules can be procured and
installed when required. Nor should the initial
equipment be designed to preclude the feasibility of
replacement or rearrangement of certain console or
panel sections or operational groups to meet future
changes of the controlled system or even the layout
and arrangement of the operations control center.
If the ultimate needs for the control center were
known, it would seem most logical to choose one
class of equipment designed for the combined
^requirements of control and data handling. This is not
fusible. Plans should be prepared for the gradual
implementation of both the conventional supervisory
control equipment for remote control and the digital
computer for monitoring and data processing.
4.8 Activation Equipment
Activation equipment refers to the power
operators for regulator devices. Self-powered
regulators such as floats and hydraulic cylinders, have
been described in 2.7,2.9,2.10 and 2.11.
Electric motor operating regulating devices have
been quite successfully employed on open-close type
regulators and have been arranged for inching
controls for intermediate positioning. Intermediate
positioning control schemes have been arranged by
using a series of limit switches and timers. In addition
to the problems encountered with electrical
equipment, the problem of loss of power is always of
concern since this is most likely to occur during a
storm which is precisely the period during which the
regulator is most likely to function.
Recent development of electric motor operators
for modulating or throttling control of valves, bring
to the user a new and more appropriate drive unit for
regulators. These drive units use low voltage, direct
current motors with direct current power derived
from silicon controlled rectifiers powered from the
standard alternating current power sources. Small.
direct current batteries, similar to car or truck
batteries, may now be used as standby power for
regulator operation during power failures. These new
motor designs can be controlled directly by presently
available electronic instruments.
In the past, reversing contactors were required
for throttling control of the standard motor. It was
the reversing contactor, not the motor, that could not
withstand continued reversing duty. The new motor
designs eliminate the reversing contactor and
continuous regulator control is possible. Gates, for
example, can be controlled automatically to maintain
a certain water level; they can be made to "hunt" in
direct or indirect relation to the rise and fall of water
level within a given band width; or they- may be
remotely positioned at any point within their full
travel by a remote set point signal from a central
control station. Gate position and water level, can be
telemetered to the control station over the same
control line. New motor operators and electronic
instruments are small, allowing them to be placed in
enclosures which protect them from exposure to
adverse conditions. This new equipment, after it has
been placed in service should prove to be of
considerably less trouble and prove, to be less
expensive to maintain. However, its initial cost will be
more than the cost of conventional equipment.
An example of a design problem using total
system control is presented in Section 7.
106
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SECTION 5
PRACTICES FOR IMPROVED OPERATION AND
MAINTENANCE OF REGULATORS AND
THEIR APPURTENANCES
CONTENTS
Page
5.1 General 109
5.2 Common Causes of Failure 109
5.3 Frequency of Inspection Required 109
5.4 Recommended Maintenance Program 109
5.5 Personnel Requirements HO
5.6 Equipment Needs HO
5.7 Safety Precautions HO
5.8 Maintenance Costs 111
5.9 Records and Data Analysis HI
107
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-------
5.1 General
Satisfactory operation of combined sewer
overflow regulator facilities depends to a large extent
on adequate, regular inspection and maintenance. The
purpose of this is twofold: First, to locate and correct
any operational failures; and second, to prevent or
reduce the probability of such failures.
5.2 Common Causes of Failure
Some of the factors causing failure as related to
regulator types are as follows:
1. Static regulators
a. Clogging
b. Sating
2. Dynamic-semi-automatic
a. Clogging
b. Silting
c. Sticking (lack of lubrication)
d. Parts failure
e. Corrosion
3. Dynamic-automatic
a. Clogging
b. Sticking (lack of lubrication)
c. Parts failure
d. Power failure
e. Water pressure failure in float-actuated,
hydraulically operated units
Of these factors, clogging is the principal
offender. It affects all types of regulators to some
extent and is practically impossible to eliminate
entirely. Silting affects most regulators, but it can be
controlled by regular flushing of the regulator station
by the maintenance crew. The other factors apply to
mechanical, electrical, or hydraulic types of
regulators and their effects can be eliminated or
minimized by proper inspection and maintenance.
5.3 Frequency Of Inspection Required
The susceptibility to clogging, to an important
degree, determines the required frequency of
regulator inspection. Several things affect this
susceptibility. They include the type and size of
regulator, the size of the combined sewer, the size of
the connection to the interceptor, and the quantity
and quality of the combined sewage.
Experience has shown that regulators of the
orifice type, or which depend on an orifice for
operation, particularly the horizontal orifice and
leaping weir, readily clog, especially when the orifice
is small.
Horizontal orifices, or drop inlets, protected by
grates appear to be more subject to frequent clogging
than any other type of regulator. Even daily
inspection and cleaning may not be adequate to
insure proper operation of this type of regulator.
Practice in the jurisdictions included in the
National Investigation varies from daily or more
frequent inspections to as few as three per year. The
average number of inspections is approximately 70
per year.
Inspection must be as frequent as required to
keep the regulators in as continuously operable
condition as practicable. In general this will require
an inspection schedule of at least each week and after
every storm. Small orifices and drop inlets with grates
will require more frequent inspection. It is
recommended, however, that no regulator be
inspected less frequently than twice per month and
after each storm.
Experience will indicate which regulators require
more frequent attention than others. The schedule
should be adjusted to meet local or changing
conditions. In this way maximum efficiency of
operation will be achieved with minimum use of
personnel.
5.4 Recommended Maintenance Program
The regulator chamber should be cleaned after
every storm and more frequently if necessary to
maintain satisfactory working conditions in the
chamber.
For all types of regulators, each visit should
include a visual inspection of the regulator and
removal of any debris preventing or tending to
prevent its operation. Preventive maintenance
programs recommended for the various types of
regulators are as follows:
1. Static Regulators
a. Orifices
Orifices clog frequently. Maintenance
equipment should include hooks, sewer rods,
and scoops, so that as much clearing of
debris as possible may be effected from the
ground surface. The regulator chamber may
then be flushed out, also from ground
surface.
b. Drop Inlets and Leaping Weirs
Grates protecting drop inlets should be
checked to be sure they have not been
damaged or weakened by corrosion. Inlets,
particularly large ones without gratings
should be fitted with grates or guard rails for
the protection of the maintenance crew, as
well as prevention of the entrance of large
objects. Where blockages are excessive the
gratings should be replaced by ones with
larger openings. Leaping weir plates must be
lubricated and adjusted semi-annually to
prevent "freezing'.'
109
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c. Side-Spill Weirs
Weir crests should be inspected for
damage and be repaired promptly.
d. Manually-Operated Gates
Manually operated gates should be
operated on a regular basis through the full
range from the open to closed position and
reset at the proper opening. The floor stand,
if any, operating stem and guides should be
freed of corrosion and be well lubricated.
2. Dynamic Regulators
a. Float-Operated Gates
If possible float-operated gates should be
operated through a complete cycle. Float
wells should be cleared of deposits of sand or
sludge and all accumulations of debris should
be removed from the float and float well.
Chains and gears should be cleaned of rust
and other deposits and thoroughly
lubricated. All parts of the mechanism
should be examined for wear or corrosion
and, if necessary, promptly replaced or
repaired.
b. Tipping Gates
Tipping gates should be checked to be
sure they move freely on the pivot shaft.
Adequate lubrication of the bearings is
essential. In some cases it may be advisable
to replace existing shafts and bearings with
stainless steel shafts and bronze bearings.
c. Motor-Operated Gates
Motor-operated gates should be operated
through the full range from open to closed
position and reset at the proper opening.
Where remote control is provided, the cycle
should be run through, using the remote
controls while the maintenance crew
observes the operation and checks the final
setting of the gate. Water level indicating and
transmitting equipment should be checked to
insure that it is functioning properly and
measuring water levels accurately. All
equipment should be inspected for signs of
wear or corrosion, repaired or replaced, if
necessary, and properly lubricated.
d. Cylinder-Operated Gates
If possible, cylinder-operated gates
should be operated through a complete
cycle. Float wells should be cleared of
deposits and all accumulations of material
should be removed from the float and float
well. Strainers on the water supply line
should be cleaned and inspected. Water
supply lines, valves and cylinders should be
inspected for leakage; and the pressure
available at the cylinder under all operating
conditions should be checked. Water level
sensing equipment on hydraulically-oil-
operated gates should be checked to insure
that it is functioning properly and
accurately. All equipment should be
inspected for signs of wear or corrosion,
repaired or replaced, if necessary, and
properly lubricated. Cross-connection
hazards should be detected and corrected to
prevent pollution of public water supplies.
5.5 Personnel Requirements
Maintenance of regulators should be carried out
by crews of three to five men, depending on the type
and complexity of the regulators used, A minimum
crew of three men is recommended in order that one
man may remain on the surface while two men enter
the chamber.
For simple regulators, three-man crews with one
foreman to direct several crews should be
satisfactory. Where remote controls, water level
sensing devices and motor-operated gates are used, a
crew of five men, including a technician and foreman
may be required.
The number of crews required will depend on the
number and types of regulators and the frequency
with which they must be inspected.
5.6 Equipment Needs
Adequate equipment should be provided for the
safety and efficiency of activities of the maintenance
crew. The following items of equipment are
considered necessary:
a. A P/i-ton panel truck with a two-way radio,
winch and A frame
b. 110-220 volt portable generator
c. 1 and 2-hp submersible pumps
d. One lV£-hp blower unit
e. Various chains, ropes, hoses, ladders, pike
poles, sewer hooks, sewer rods, chain jacks, tool
kits, etc.
f. One oxygen deficiency meter, one
explosimeter, and one H2 detection meter, safety
equipment, helmets, harnesses, first aid kits,
danger flags, signs, barricades, life jackets, flares,
gas masks or air packs, gas detector lamps, fire
extinguishers, extension cords, rubber jackets,
pants, boots, waders, etc.
g. Spare parts.
5.7 Safety Precautions
Precautions necessary to protect the maintenance
crews from the hazards in the sewers and regulator
110
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chambers and from traffic are relatively uniform
throughout the country. The following instructions,
issued to the crews in Philadelphia, are typical:
1. Truck should be parked so as not to obstruct
traffic but, if possible, should be used to protect
men working near the open manhole. If truck is
used for this purpose, suitable flashing lights
must be used on the truck.
2. Warning cones, flags, signs, and lights should
be used to make areas safe for both vehicle and
pedestrian.
3. Manhole cover should be raised with a safe
tool and bar placed under it so that it can be
rolled to one side.
4. A manhole guard should be placed around
the open manhole.
5. The air in both sewer and chamber should be
checked for explosive mixtures and hydrogen
sulfide. Oxygen deficiency should be checked.
7. If there is an indication of gases, the portable
blower should be used to clear the area.
In addition to the above safety precautions it is
considered essential that at least one man remain at
the surface at all times to summon or render
assistance in the event of an accident.
5.8 Maintenance Costs
The cost of maintaining sewer regulators, as
reported in the National Survey, varies widely. In
most cases the reported expenditures are probably
not adequate to maintain the regulators in completely
satisfactory condition. The annual cost per regulator
required to conduct a satisfactory maintenance
program is estimated to be as follows:
Description
Vertical orifice
or siphon
Leaping wen-
Drop inlet
Side-spill weir
Manually operated
gate
Float-operated
gate
Tipping gate
Cylinder operated
gate
* From Report, Section 5
Annual Cost
per Regulator*
$ 600 - 800
700- 900
1200-1500
400- 500
900-1100
1100-1200
1100-1300
1200 -1300
5.9 Records and Data Analysis
Complete records should be kept of all inspection
and maintenance work. The time and date of each
inspection should be recorded together with a
description of the condition of the regulator and the
work performed. The number of man-hours spent at
each regulator should be noted.
The data obtained should be tabulated for each
regulator and summarized for each type of regulator.
These records will quickly reveal any regulators which
require excessive maintenance or are out of operation
with unusual frequency. The causes should then be
investigated and, if possible, corrected.
The records also will provide the data needed to
compare the cost and efficiency of different types of
regulators for guidance in the design of new
regulators or the remodeling of existing regulators.
Ill
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SECTION 6
DESIGN AND LAYOUT, AS INFLUENCED BY
OPERATION AND MAINTENANCE -
TYPICAL CRITERIA AND DETAILS WITH RESPECT TO
OPERATIONS AND MAINTENANCE
CONTENTS
6.1 Typical Layout Criteria
6.2 Materials
Page
. 115
. 117
113
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6.1 Typical Layout Criteria
6.1.1 General
The layout of a regulator station should meet
two criteria: The first, based on the hydraulic
requirements; and the second, based on the operation
and maintenance requirements. Very often the
designer gives little attention to operating and
maintenance requirements, with the result that the
regulator fails to function properly due to^ lack of
adequate maintenance. Hydraulic design principles
have been outlined in Section 2. This Section
considers the layout from the viewpoint of operation
and maintenance.
6.7.2 Location
The designer may have little choice with regard
to the location of the regulator. Regulators often
must be located on existing combined sewers. Where
the area is highly developed and there is no choice
except to place the regulator station within the street
right-of-way. If the street is a cul-de-sac and
terminates at the water's edge it may be possible to
fence off the end of the street for the regulator site.
Where areas are partially developed, it may be
possible to relocate the combined sewer so as to place
the regulator on a site other than the traffic
right-of-way. For maintenance purposes and for
operator safety this is most desirable. If this is not
possible, access to the facility should preferably be
from the rear of the curb in order not to block traffic
while routine maintenance is being performed.
6.1.3 Access
Separate access should be provided to each
chamber of the regulator station. This is necessary
when the chambers are small or the maximum level of
the sewage in the chamber is near the ground surface.
In large chambers where the depth permits,
access to the diversion and tide gate chambers may be
combined.
Access to regulators located in streets is made
through conventional manhole shafts with a vertical
ladder or with manhole steps set 12 inches on centers..
If the regulator is deep, stairs should be used at a
reasonable level below the ground surface.
When the regulator is located off the street,
consideration should be given to alternate means of
access rather than the standard manhole. If there is
objection to a structure extending above ground,
access can be provided by a floor door or hatch and a
ship's ladder. A ship's ladder is a fixed inclined ladder
with an angle to the horizontal of beteen 40 and 56
degrees. The minimum width of tread between
stringers should be two feet. Ladders steeper than 56
degrees should not be used.
Where there is no objection to a superstructure,
stairs can be provided. This increases the length of
superstructure opening to 11 feet and requires a
superstructure approximately 13 feet long, 5 feet
wide, and 8 feet high. Details of such a stairwell are
shown in Fig. 6.1.3. If a superstructure is required for
electrical equipment the stairwell superstructure may
be built adjacent to its exterior wall.
Spiral stairs should be considered where space is
not available for standard stairs. These are
constructed in various diameters, from 4 feet,
considered a minimum for ease of access, to 6 feet or
more depending on the requirement. They are usually
constructed with either 12 or 16 treads to a complete
circle. On a 12-tread circle, 9-inch risers will provide 6
feet 9 inches of headroom, and on a 16-tread circle
7-inch risers will produce 7 feet of headroom when
calculated on the basis that three-fourths of the
vertical height of a full circle is required for free
passage.
6.1.4 Light, Heat and Ventilation
As a rule, insufficient consideration is given to
light, heat and ventilation in regulator chambers of
average size, particularly when no electric power is
required for operation of the regulating device.
Portable lamps are usually used for lighting
purposes. When the chambers are large, at least two
manhole openings should be provided for each
chamber for adequate light and ventilation. If the
regulator is located below the point of access and is
properly fenced, roof gratings can be used to increase
light and ventilation. Whenever electric power is
available at the regulator chamber, provision for
electrical lighting in all parts of the-regulator station
is normal.
Heating is not considered necessary in
underground chambers for the comfort of personnel.
However, when dehumidifiers are used to prevent
corrosion of electrical equipment, heating is
sometimes provided to prevent freezing of the
dehumidifiers and to reduce the relative humidity.
Superstructures, if used, should be heated.
Shallow regulator stations using static regulator
devices requiring little attention can be adequately
ventilated by use of portable blowers. Such chambers
should be tested for flammable gas or oxygen
deficiency before entering. In deep chambers tests
also should be made for the presence of carbon
monoxide and hydrogen sulfide. Where mechanical
equipment is used consideration should be given to
the installation of ventilating equipment. Such
ventilating equipment is considered essential for wet
wells in sewage pumping stations. Present
115
-------
FIGURE 6.1.3
-SURFACE
RISER 10.0"
EFFECTIVE TREAD 6.7"
SHIP'S LADDER WITH t'-G" X 6'-On DOOR
50"
I ^ounrMV/c. I
RISER 9.25
EFFECTIVE TREAD 7.8"
SHIP'S LADDER WITH Z-6X 8-0 DOOR
DOOR 2-6" X 6'- 8"
SURFACE
RISER 8.0
TREAD 9.5"
SUPERSTRUCTURE DIMENSIONS
I3'-0"X 5'-0"x 8'-0"
STAIRWAY WITH SUPERSTRUCTURE
ACCESS STAIRS
116
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recommendations for such use by health authorities
("Recommended Standards for Sewage Works."
Great Lakes-Upper Mississippi River Board of State
Sanitary Engineers, 1968) include: (1) Provide at
least 30 complete air changes per hour for
intermittent ventilation; (2) interconnect
intermittently operated ventilating equipment with
the lighting system; and (3) introduce fresh air into
the wet well by mechanical means. The
recommendations for pumping station wet wells,
noted above, should be equally applicable to
regulator chambers containing mechanical equipment
and requiring frequent inspection.
6.1.5 General Features
The designer should visualize all possible
activities of maintenance personnel and attempt to
provide adequate and convenient facilities in which
they can perform their duties. Walks or platforms,
preferably above the maximum sewage level, should
be provided so that all parts of the regulator station
can be reached and so that the inlet and outlet sewers
can be observed and are readily accessible. Benches
for access landings should have a minimum width of
l]/£ feet. Headroom should be at least 6% feet.
Guard rails should be provided around all
openings or sudden drops. However, officials of one
city interviewed in the National investigation stated
that they generally do not use protective railings in
the regulator chambers since the staff feels that
reliance on a railing which may fail due to corrosion
is more hazardous than the omission of the railing.
However, this city uses railings of structural steel,
encased in concrete, to prevent failure due to
corrosion at regulator stations that are particularly
hazardous and where a fall might mean death or
serious injury.
Cast iron stop plank guides should be provided to
shut off or divert flow to, or from a channel when
required for maintenance purposes.
6.1.6 Gates
The sluice sizes available from one manufacturer
are shown in Table 6.1.6. Normally the smallest size
used in a regulator chamber should be 12 by 12
inches.
When a cylinder-operated gate is activated by
water pressure the gate size is generally limited to a
maximum of nine square feet. The size of gate when
oil pressure is used is not limited.
A shaft and ground surface opening should be
provided over each gate. The dimensions of this
opening should be at least one foot greater in each
direction than the overall dimensions of the gate, to
allow quick, problem-free operation or removal.
6.2.7 Float Well
The float well should have minimum dimensions
of three feet square. The bottom of the well is set
above, the invert of the adjacent channel and
connected thereto with a 12-inch wide passage or
telltale. The telltale should be aimed downstream
from the float well to prevent floating solids from
entering the well or plugging the telltale.
6.2 Materials
6.2.1 Metals
The best of the bronzes for corrosion resistance
and strength is silicon bronze. This is a very high
copper, zinc-free bronze. Manganese bronze castings
and extrusions wear well. They are used for valve
seats and operator stem nuts for this reason. Among
the stainless steels, the 18-8 chromium-nickel content
percentage respectively endures best. Types 303, 304,
and 305 are used for valve stems, studs, nuts and
bolts. Type 326 stainless steel is especially good in sea
water and less costly than monel which also gives
excellent service in salt water. Heavy body castings
are usually grey iron castings, conforming with ASTM
specification A126, Class B. However, in highly
corrosive applications, Ni-Resist Type 1A has been
used successfully. This is a trade name of
International Nickel Company for an iron-casting
with the following percentage composition: 14%
nickel, 6% copper, 2%% chromium. Both cast iron
and wrought iron are customarily coated with a hot
coal-tar enamel in accordance with AWWA
Specification C2031 Bronze, stainless steel and monel
are not usually coated.
Sluice gates.generally should conform to AWWA
Standard C501. This standard also covers sluice gate
operating mechanisms of the manual, electric-motor
and hydraulic-cylinder types. The latter type is oil
operated at 2000 psi working pressure. The .Suma
Standard, Sect. 103, states that the purchaser may
specify other operating media or pressures, as desired.
One manufacturer has suggested four combinations of
materials for sluice gates for use under various
conditions. These combinations are shown in Table
6.2. Combination No. 1 which meets AWWA
Standard C501 is not considered satisfactory for use
in raw sewage service because it contains naval
bronze. De-zincification, where zinc is dissolved from
bronze leaving a weak, porous material, can occur
with naval bronze in contact with either acid or alkali
fluids. The low zinc content of phosphor or silicon
bronze enables these alloys to resist de-zincification.
Material Combination No. 3 would provide
117
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TABLE 6.1.6
SLUICE GATE SIZES
Size of Gate
Inches
" Rectangular
Width X
Height
6x 6
8x 8
10x10
12x12
12x18
12x20
12 X 24
14x14
15x15
16x16
16x24
18x12
18x18
18x24
18x36
20x20
20x24
20x36
24x12
24X18
24x24
24x30
24X35
24x48
24x60
30x24
30x30
30x36
30x48
30x60
Circular
Diameter
6
8
10
12
14
15
16
18
20
21
24
30
36
Area of
Clear Opening
Square Feet
.1964
.2500
.3491
.4444
.5454
. .6944
.7855
1.000
1.500
1.667
2.000
1.0S9
1.361
1.227
1.562
1.396
1.778
2.667
1.767
1.500
2.250
3.000
4.500
2.182
2.778
3.334
5.001
2.405
3.142
2.000
3.000
4.000
5.000
6.000
8.000
10.000
4.909
5.000
6.250
7.500
10.000
12.500
7.068
Size of Gate
Inches
Rectangular
Wldlh X
Height
36x18
36x24
36x28
36x30
36x36
36x42
36x48
36x60
36x72
36x84
42x24
42x27
42x30
42x36
42x42
42x48
42x60
42x72
48x27
48x30
48x36
48x48
48 X 54 .
48x60
48x72
48x84
48x96
48x108
54x48
54x54
54x72
60x36
60x48
60x60
60x72
60x84
60x96
66x66
Circular
Diameter
42
48
54
60
66
Area of
Square Feet
4.50
6.00
7.00
7.50
9.00
10.50
12.00
15.00
18.00
21.00
9.62
•7.00
7.88
8.75
10.50
12.25
14.00
17.50
21.00
. 12.57
9.00
10.00
12.00
16.00
18.00
20.00
24.00
28.00
32.00
36.00
15.90
18.00
20.25
27.00
19.64
15.00
20.00
25.00
30.00
35.00
40.00
23.76
30.25
Size of Gate
Inches
Rectangular
Wldlh X
Height
66x72
72x42
72x48
72x60
72x72
72 x 84
72x96
78 x 78
78x96
84x36
84x60
84x72
84x84
84x96
84 X 108
96x48
96x60
96x72
96x84
96X96
92x120
96x144
108x48
108 x 60
108x108
120x42
120 x 72
120x84
120 x 96
' 120x120
120x190
144 x 48
144 x 144
Circular
Diameter
72
78
84
88
90
96
102
108
120
Area of
Clear Opening
Square Feet
33.00
28.27
21.00
24.00
30.00
36.00
42.00
48.00
33.18
42.25
52.00
38.48
21.00
35.00
42.00
49.00
56.00
63.00
42.20
44.18
50.26
32.00
40.00
48.00
56.00
64.00
80.00
96.00
56.75
63.62
36.00
45.00
81.00
78.55
. 35.00
, 60.00
;?o:oo
80.00
100.00
158.33
48.00
144.00
Courtesy Rodney Hunt Co.
118
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TABLE 6.2
SLUICE GATE MATERIALS
Material Specifications:
CAST IRON
AOSTEN1TIC GRAY IRON
CASTING (Ni-Resist)
STAINLESS STEEL (Seating
Faces and Anchors)
MONEL (Faces and Fasteners)
MANGANESE BRONZE (Lift
Nuts and Wedges)
NAVAL BRONZE (Faces and Stems)
PHOSPHOR BRONZE (Faces)
SILICON BRONZE (Fasteners)
SILICON BRONZE (Castings)
STAINLESS STEEL (Fasteners)
STAINLESS STEEL (Stems
and Anchors)
A126, Class B or C
A 436, Type 2 or 2b
A 276, Typo 302 or 304
B164, Class A or B
B147, Alloy 8A
B 21, Alloy B
B139, Alloy A
B 98, Alloy A, B or D
B198, Alloy 12A
A 320, Grades BS or B8F (Bolts)
A194, Grades 8 or 8F (Nuts)
A 582, Type 303
Material Combinations:
Gate Part or Hem
of Asssrably
WALL THIMBLE
#1 Material #2 Material #3 Material ^4 Material '
Combination : Combination Combination Combination
Cast Iron
Cast Iron
Cast Iron
Ni-Resist
CATE ASSEMBLY
FRAME AND SLIDE
SEATING FACES
YOKE (NRS ONLY)
SIDE WEDGE BLOCKS
CONTACT FACES
SIDE WEDGES
TOP AND BOTTOM
WEDGES
FASTENERS
Cast Iron
Naval Bronze
Cast Iron
Cast iron
Naval Bronze
Manganese Bronze
Manganese Bronze
Silicon Bronze
Cast Iron
Stainless Steel
Cast Iron
Cast Iron
Stainless Steel
Stainless Steel
Stainless Steel
Stainless Steel
Cast Iron
Phosphor Bronze
Cast Iron
Cast Iron
•°hosphor Bronze
Silicon Bronze
Silicon Bronze
Silicon Bronze
Ni-Resist
Monel
Ni-Restst
Ni-Resist
Monei'
Monel
Mone!'
Monel
FLUSH BOTTOM ASSEMBLY
STOP PLATE AND
RETAINER
Cast Iron
Cast Iron
Cast Iron
Ni-Resist
STEM ASSEMBLY
STEM
STEM BLOCK
STEM SPLICE
Stainless Steel
Manganese Bronze
Stainless Steel
Stainless Steel
Ni-Resist
Stainless Steel
Stainless Steel
Silicon Bronze
Stainless Stee!
Monel
Ni-Resist
Monel
119
-------
compatible materials for this condition. Combination
No. 2 would also satisfy this condition.
Ammonia-bearing fluids such as raw sewage may
cause stress-corrosion cracking to which copper based
alloys are extremely susceptible. Since the 300 Series
of stainless steel is not affected by stress corrosion
cracking, the No. 2 Material Combination replaces
with stainless steel all bronze gate parts subject to
high stress. Combination No. 4 is intended only for
salt or brackish water installations and combines the
most corrosion-resistant materials.
Piping for air, water or oil should be
corrosion-resistant. A suitable pipe for this purpose is
seamless red brass pipe meeting ASTM specification
B43. Suitable fittings for this pipe are copper-base
alloys meeting ASTM specification B30, Alloy 4B.
Manhole steps usually are made of cast iron or
aluminum. Vertical ladders usually are made of
galvanized steel or aluminum. Ship's ladders can be
fabricated with either galvanized steel or aluminum
stringers and either cast iron or cast aluminum
abrasive treads. Spiral stairs also can be obtained with
cast iron or cast aluminum treads. Normally the
center column is a 3 to 4-inch-diameter steel pipe; for
regulator use the center column should be stainless
steel. Aluminum used in the foregoing is usually
specified to be 6061-T6, 6063-T5, 6063-16 and
6063-T832.
6.2.3 Elastomers and Gasket Materials
The most commonly used elastomer is Neoprene.
Neoprene is a copolymer of butadiene and acrylic
nitrile. It has good resistance to hydrocarbons and
ozone and resists air-hardening. Nitrile and a blend of
nitrile and polyvinyl chloride also have good
resistance to the sewage atmosphere. Natural rubber
deteriorates in sewerage applications and is not
recommended. Gaskets and packing should be made
of asbestos, teflon coated asbestos or tallow
lubricated flax.
6.2.4 Electrical
Motors located in underground chambers or in
above-ground chambers into which sewer atmosphere
may escape should be explosion-proof conforming to
National Electric Code Article 500 for Class I, Group
D, Division I locations. Wires should be in conduits of
corrosion-resistant materials such as polyvinyl
chloride.
6.2.5 Plastics
Although plastics and plastic-coated metals have
not been used to any appreciable extent in combined
sewage regulator installations, they offer considerable
promise for the future. Coatings such as epoxy, vinyl,
nylon, and celloplosic applied by the fluidized bed
process all endure well in sewage service. They are
quite abrasion-resistant, an important consideration
as combined sewage contains much grit. These
coatings applied to steel and aluminum offer
maximum corrosion resistance, coupled with good
strength characteristics.
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SECTION 7
EXAMPLE OF SYSTEMS CONTROL
THROUGH INSTRUMENTATION
CONTENTS
Page
7.1 General 123
7.2 Description of Project Problem 123
7.3 Project Requirements 124
7.4 Comments 132
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7.1 General
The following example of total system control of
a hypothetical combined sewer system through the
use of instrumentation, automation, and data control
devices, has been developed to provide a practical
demonstration of the application methodology
required for its implementation. The intent of the
section is to examine how an effective control system
may be developed.
7.2 Description of Project Problem
CENTROPOLIS
PROJECT NO. 5468
CONTRACT 13
REGULATING STATION NO. 5
General This will be located near Eight-Mile creek at
approximately Station 28+00 on the Eight-Mile
interceptor just west of the west right-of-way line of
Highway 6 out of Worden. Ground elevation is
approximately 885. The City has entered into a
contract with the adjacent Minneola Sanitary District
to divert part of the combined sewage from this
interceptor to a new system which will allow the
postponement of treatment plant expansion for
several years. The structure will be similar in
appearance to Station No. 2 for Appenouse which
was completed this spring. A downstream regulated
weir will be part of another contract.
Head Conditions Maximum hydraulic gradient at the
regulating station influent will be EL. 870. Minimum
gradient is assumed to be El. 845. Minimum gradient
of the connection to the Minneola interceptor will be
El. 820 and maximum gradient may approach El.
862.
Flow Limitations The present contract limits the
maximum rate of diversion under any condition to
500 gpm. In addition, the maximum rate of diversion
from 3:00 p.m. to 9:00 p.m. on any day when the
temperature -is 90°F or higher is limited to the
average hourly diversion rate during the 24 hour
period ending at 9:00 a.m. on such date.
Equipment The station will contain the following
major items of equipment:
1. One throttling gate. This gate normally shall
remain fully open for gravity flows up to the
amounts limited by the contract. For higher
flows the gate shall then be automatically
throttled to maintain the flow within the
contracted amounts.
2. One mechanically operated check gate to
automatically prevent backflow through the
check gate. This will require no control or
electric equipment.
3. Two 125-horsepower variable speed pumping
units, each sized to deliver up to the contracted
maximum quantity under any imposed head
condition. Either pumping unit may be selected
as the lead pump with the other serving
automatically as a standby pump if the lead
pump fails. Pumps shall always start at a
minimum speed.
4. Each variable speed pump will have a
discharge valve of a particularly low allowable
working pressure. It will, therefore, be necessary
to design the control to prevent a differential
pressure across the valve in excess of 10 psi.
5. Influent level shall be measured at Station
43+00, approximately 7500 feet upstream from
the diversion regulating station. Control shall be
such that at a certain adjustable low level the
regulating station will shut down to prevent any
diversion from the Eight-Mile interceptor.
6. The regulation station effluent flow shall be
metered and used for feed-back to the control.
The control and instrument designer shall
investigate and determine the type of metering.
The effluent conduit will be 36-inch concrete
pipe.
7. The Minneola Sewer District plant influent
screen chamber wet well level shall be measured
and telemetered to the regulating station. At an
adjustable plant influent high level, the regulating
station shall be shut down.
8. Provision shall be made for two incoming
480-volt, 3-phase, 60-hp. services. Only one
service is to be installed originally with space for
the second service in the future.
9. Gate and valve operators shall be' electric or
pneumatic with independent opening and closing
speed adjustments.
10. Pumps, motors and controls shall be housed
indoors, separated from sewers. The building
shall be force-ventilated.
Sequence Of Operation The station controls shall be
such that the flow diverted from the Centropolis
Eight-Mile interceptor will be maintained at a
set-point rate, adjustable between 200 gpm and
1200 gpm. The sequence should be such that first the
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throttling gate opens slowly when Eight-Mile
interceptor reaches Elevation 1.5 at level measuring
Station 43+00. If the hydraulic conditions are such
that set-point flow can be maintained by gravity, the
throttling gate shall be 'automatically positioned
to effectively operate as a rate-controller. As the level
rises and set-point is maintained by the gate no
pumping is required.
If the hydraulic conditions are such that the
throttling gate is open, the level remains above 0.5
feet at the level measuring station, and the diverted
flow is less than set-point quantity, the lead pumping
unit should start at minimum speed and rise in speed
slowly to deliver set-point flow. In this case the
pumping unit shall continually vary in speed to
effectively operate as a rate-controller. The pumping
unit discharge valve should not commence to open,
however, until the pump discharge pressure is greater
than the station discharge pressure. During the
sequence of putting the pumping unit on line, the
speed also should be such as to limit the differential
pressure across the pump discharge valve to a
maximum of 10 psi. It may be decided not to start
the lead pump until the level reaches approximately
2.0 feet at Station 43+00. If, due to malfunction, the
lead pump should fail to start, the standby pump
should be started in a similar pump and discharge
valve control sequence whenever the Eight-Mile
interceptor level rises to Elevation 2.25. In this case
the standby pump is to effectively operate as a rate
controller to maintain set-point diversion
rate-of-flow. The two pumps shall never operate in
parallel.
Pumping, once commenced, shall be maintained
until the Eight-Mile interceptor level falls to 1.0 foot,
in which case the .pump speed shall be reduced to
minimum, the discharge valve slowly closed, and
finally, the pumping unit stopped.
High water level at the Minneola Sewer District
Plant No. 1 shall override all controls and shut down
the regulating station by stopping the pumps and
closing the throttling gate.
In case of power failure, an over-riding control
shall slowly close the throttling gate and pump
discharge valves.
Arrangements shall be made for the future
monitoring of station equipment status and alarm
conditions at the proposed Operations Control Center
whenever it is designed.
Miscellaneous During the first years of operation it is
anticipated that the required quantity of diverted
flow by gravity through the regulating station will
sometimes, under certain hydraulic conditions, not be
of sufficient quantity to fill the interconnecting
conduit during normal contracted flow rate.
Therefore the flow meter must not be of a design
requiring a filled pipe.. Flushing water will not be
available for several years.
The final selection of the throttling gate and
check gate has not yet been determined.
The plans and specifications must be completed
in early June to be eligible for appropriations
approved for this project. Plans and specifications are
80 percent complete. Rather than delay the project,
certain detailed features of equipment may have to be
modified and covered by change order after award of
contract.
7.3 Project Requirements
This is a common situation. The project must
meet a certain deadline. The problem is defined. The
solution is somewhat hazy, however, depending upon
the ingenuity of the control and instrumentation
designer together with those of each of the other
disciplines involved.
At this point the designer will begin to conceive
the parts and their relationship to the whole. These
parts or subsystems will be reduced to functional
block diagrams and schematics. These subsystems will
then be put into greater systems until all are
combined into one system.
It is not feasible or practicable in many cases to
wait until all of the necessary details are resolved
before proceeding with the scheme of control. In this
case, it is recognized that some suitable means for
metering flow must be determined, and that this may
be a real hurdle but for the purpose of starting the
control schematic this is assumed possible and the
development of the scheme is taken from the point of
a metering signal representing flow. The control
designer can make other assumptions too, such as the
means of varying the speed of the pumps. In this case
it can be assumed that some type of slip coupling can
be used for speed regulation; then, if some other
means of variable speed drive is selected the control
scheme can be modified to conform to that particular
drive circuitry.
It may be, as in this case, that the throttling valve
and check gate may not be definitely determined as
to type, manufacturer, etc.; however, the control
designer must assume that such equipment will be
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found and that it can be driven by standard type
operators. Again, the control designer may have some
misgivings regarding the hydraulics, as defined in the
memorandum; however, he must proceed upon the
assumption that such information is reasonably
correct or will be corrected. It also must be assumed
that suitable means of communications links, such as
leased telephone lines will be made available, the
details of which can be ascertained later. All of this is
simply to show that the instrumentation and control
scheme can be commenced early in design stage, as it
certainly should be, since its development points out
more clearly all of the special requirements of the
system equipment.
The control designer will choose from his past
experience whether to use as a basic control media
pneumatic, hydraulic, or electric devices, or perhaps a
combination of such instruments. In this particular
case, he chooses to use both pneumatic and electric
systems with some hydraulic devices for timing
control.
For those who are interested in examination of
yet more detail that must be conceived, an example
of the functional block diagrams and schematics for
this hypothetical project is shown in the following
figures together with a written description of the
actual performance of each particular element
employed.
The block chart is a typical exercise in the logic
that must be conceived and employed in the design
development of a control scheme. The diagram is
used to describe the instrumentation, whereas
schematics are used to describe the electrical circuits.
By reference to these diagrams while reading the
following steps, one can follow the design logic used.
No two designers would necessarily arrive at the same
means of solution. For example, whereas this solution
has used a considerable number of pneumatic control
devices, the problem could be solved using almost all
electric and electronic equipment.
It has been assumed that the station would best
be designed to function automatically with local
controls, then to superimpose the necessary remote
control features after this local automatic mode of
control is fully explored and developed. This is
reasonable since the station must be constructed to
be operable locally for such contingencies as loss of
remote control facilities, or even to be operated prior
to the construction of the Central Operations Center.
Details, such as time of day that certain rates might
be allowed are also disregarded at this stage of the
design, since they too can be assumed to be
superimposed on the basic scheme.
The following describes the step-by-step features
for both the local-automatic and the local-manual
control modes:
Automatic Control
1. The Eight-Mile interceptor waste water level,
measured over a five-foot control range for
control accuracy only regardless of overall depth,
is telemetered from the measuring station to a
telemetering receiver at the regulating station.
The telemetering receiver is equipped with
adjustable contacts for control circuit switches,
as follows:
EM-1 Normally open contact, closes on
rising level at 0.5 feet and remains closed
above. This contact prevents pumping when
the interceptor level is below 0.5-feet.
EM-2 Normally open contact, closes on
rising level at 1.0-foot and remains closed
above. This contact prevents pumping when
the interceptor level is below 1.0-foot.
EM-3 Normally open contact, closes on
rising level at 1.5-feet and remains closed
above. This contact prevents the regulating
station beginning operation until the
interceptor level rises to 1.5-feet.
EM-4 Normally open contact, closes on
rising level at 2.0-feet and remains closed
above. This contact prevents the beginning of
any pumping to commence until the level
rises to 2.0-feet.
EM-5 Normally open contact, closes on
rising level at 2.25-feet and remains closed
above. This contact prevents any standby
pumping to commence until the level rises to
2.25-feet.
EM-6 Normally closed contact, open on
rising level at 0.05-feet and remains open
above. This contact can be used for
monitoring and alarm of the level measuring
equipment by sensing an essentially zero
level measurement.
2. The Minneola sewage treatment plant
influent wet well level is measured and
telemetered to the regulating station. The
regulating station is not to operate during the
time that this plant is over-loaded. Contacts are
therefore provided in the plant level telemetering
receiver for use in the control circuits. Only one
contact, STP 1, which is normally closed and
opens on rising level at some high level setting is
required.
3. A rise in waste water level on Eight-Mile
interceptor to 1.5-feet closes receiver contact
125
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EM-3, which is in series with the Minneola plant
level receiver contact STP-1, to complete a
control circuit through relay R2 to energize relay
R2.
4. When relay R2 is picked up (energized) it
seals itself in through one of its own contacts R2
so that it will remain energized until power to the
relay is interrupted by either a fall in the
intercepter level to 0.5 feet causing the level
contact EM-1 to open or high level at the plant to
cause contact STP-1 to open. It should be noted
that relay R2 has a number of contacts which
will be called upon to perform various functions
and that relay R2 will act as sort of a master
switch for placing the station into service and for
taking it out of service.
5. One of the relay R2 contacts will close when
the relay is energized to energize solenoid valve
"A" that connects the station rate setter output
signal to rate controller No. 3 which in turn
controls the position of the throttling gate
allowing flow by gravity through the station at a
controlled or regulated rate as required by the
rate setter. Relay R2 contacts also partially
enable circuits, that is they help to set up
circuits, for solenoid valves 1A, IB, 2A and 2B,
on pumping units No. 1 and No. 2 respectively,
should their operation become required.
6. The throttling gate, the flowmeter and the
controller function as a rate controller under this
condition to maintain the set-point flow rate as
determined by the rate setter. The rate setter
develops an output signal representing the desired
rate of flow. Controller No. 3 receives this signal
as its input and compares it with the feedback
signal which represents actual flow. The output
of controller No. 3 automatically varies as
required to position the throttling gate to that
position necessary to establish an actual flow
signal equal to the set-point signal. Under this
condition the actual fl w is equal to the desired
or set point flow. This is referred to as closed
control loop with feedback.
7. If the Eight-Mile interceptor level falls to a
level below 0.5 feet, relay R2 is de-energized,
switching the controller input set-point signal line
to exhaust (zero flow signal) causing the
throttling gate to close to satisfy the zero flow
signal. This, in effect, shuts down the station,
after it normally has functioned by gravity flow
for a period, without having entered a pumping
stage.
8. If the desired (set-point) flow cannot be
maintained by gravity flow through the throttling
gate, the gate obviously will have reached the
fully open position, since it is positioned to try
to satisfy controller No. 3. In this situation the
diverted flow signal pressure will be less than the
rate setter (set-point) signal pressure. By sensing
the occurrence of this condition, the sensor can
be used to initiate pumping. This sensor is
differential pressure switch "A".
9. Differential pressure switch "A" shall be set
to close a switch contact whenever the rate setter
output signal exceeds the flow transmitter output
signal by approximately 1.0 psi.
10. The switch contact of differential pressure
switch "A" connected in series with a throttling
gate limit switch, which closes only when the
gate is fully open, energizes the time delay relay
TD2. This time delay relay is to prevent starting
of a pump unless this condition lasts for a
reasonable period.
11. The time delay relay TD2 is adjustable from
0.2 to 3 minutes. If the throttling gate is open
and the rate of flow through the regulating
station is less than the desired (set-point) rate for
a period equal to the time delay relay setting
(one minute, for example), the time delay relay
contact TD2 closes to pick up relay R3.
12. Relay contacts R3 close to complete the
starting circuits of both pumps. It will not
complete the starting circuit on the pump
selected as "standby"; however, it will complete
the starting circuit for the pump selected as
"lead" provided there is sufficient suction level
and that the second pumping unit is not running
(a condition which could occur, for example, if it
has been started under manual control). These
conditions are imposed on the starter circuits by
the series connection of contacts Rl and M2 in
Pump No. 1 and contacts Rl and Ml in Pump
No. 2.
13. To insure that sufficient water level on the
influent to the regulating station exists for
pumping, a level switch installed on the suction
piping closes its switch contact at a measured
water depth of 3-feet and above. This switch
energizes time delay relay TD1.
14. The time delay relay TD1 is adjustable from
0.2 to 3 minutes. This relay, when energized
closes its contact TD1 instantaneously but when
de-energized the contact will delay opening for a
period equal to the time delay relay setting (one
minute, for example). Thus, loss of influent
water level must be sustained for a reasonable
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period to cause the time delay relay TD1 contact
to open. This prevents stopping the pump upon a
transient fall in water level during pump starting
that is not sustained after pumping is
commenced,
15. Time delay relay TD1 contact closes to pick
up relay Rl.
16. Relay Rl contacts energize each pump
starting circuit, discharge valve control circuit,
circuits to control the pump speed. These
contacts are used in such a manner that, if a
pump is . running, loss of water level on the
suction for a definite period de-energizes relay
Rl; causing the pump to reduce speed to
minimum, the pump discharge valves to close,
and the pump motor to stop.
17. Thus with sufficient suction water level
available, closure of relay R3 contacts as stated
above, starts the "lead" pump;
18. The pump starts at minimum speed. The
set-point signal pressure to the pump speed
controller is connected to exhaust (minimum
speed signal) through solenoid "B". Note at this
point that solenoid "B" is still de-energized.
19. When the motor starts, its motor starter
holding coil (Ml or M2) is sealed by respective
auxiliary (Ml or M2) starter contacts (Ml or M2)
in series with a "Stop" push-button contact and a
knee action limit switch on the pump discharge
valve, thus eliminating any further effect of time
delay relay TD2 and relay R3.
20. The closure of either pump motor starter
auxiliary contact (Ml or M2) picks up solenoid
"B", which switches the pneumatic set-point
signal of the speed controllers (No. 1 and No. 2)
from exhaust pressure (zero flow signal) to the
rate' setter signal pressure. This forces the
pumping unit always to start from minimum
speed.
21. The pump discharge valve is not to open
until the developed pumping head exceeds any
possible station discharge pressure by 5 psi.
Differential pressure switches "1A" and "2A" on
pumps No. 1 and No. 2, respectively, close their
contacts as soon as the pump pressure exceeds
the station discharge pressure by 5 psi.
22. Closure of the differential pressure switch
contacts (1A or 2A) completes the control circuit
through time delay relay TD5 contact, the
automatic position of the pump
"Manual-Off-Auto" switch, relay contact R2,
relay contact Rl, and the respective motor
starter auxiliary switches (Ml or M2) to the
pump discharge valve (VI .or V2) control
solenoid (1A or 2A) and relay (R5 or R6) on
pump No. 1 or No.2, respectively, to initiate
discharge valve opening.
23. When the pump discharge valve control
solenoid (1A or IB) becomes energized, it is
immediately sealed by its associated relay (R5 or
R6) contact so that the pump discharge valve
continues to travel to the fully open position.
24. Also, during the starting and stopping of a
pumping unit, the pump speed never is allowed
to cause a differential pressure across the
discharge valve in excess of 10 psi. To sense this
condition, differential pressure switch (IB or 2B)
across valve (VI or V2) on pump No. 1 or No. 2;
respectively, closes its contact when the
developed pump pressure exceeds the station
discharge pressure by 10 psi.
25. Closure of the' differential pressure switch
(IB or 2B) energizes solenoid (IB or 2B),
respectively, which switches the pneumatic
control signal to the positioner on the pump
speed potentiometer to exhaust (zero speed)
pressure, causing the positioner to start to
operate in the direction of speed reduction. As
speed is reduced to the point where the
differential across the valve is within 10 psi, the
solenoid (IB or 2B) is de-energized, thus
connecting the controller output back to the
positioner for continuation of speed control.
26. When the pump discharge valve is completely
open, the variable speed pump together with the
flowmeter and pneumatic controller associated
with that pump then function as a closed control
loop to regulate flow at the desired rate setting.
27. If the lead pump should fail to start and the
Eight-Mile interceptor level rises to 2.0 feet, time
delay relay TD3, which is adjustable from 0.2 to
3 minutes, will pick up relay R4 if this condition
persists for a period equivalent to the relay time
setting (one minute, for example).
28. Relay 4 contacts would then close to start
the standby pump. The starting sequence of the
standby pump would be as described above for
starting of the lead pump. Note, however, that
the standby pump will not start if the lead pump
is running because of the interlocking starter
auxiliary switches (Ml or M2).
29. As the hydraulic conditions vary, the variable
speed pump may go to full speed if necessary to
try to maintain the rate-set flow.
30. Also as the hydraulic conditions vary, the
variable speed pump may reduce speed to a
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minimum, .yet the flow through the station might
then exceed the rate-set (set-point) flow. When
this condition develops, the station obviously
could perform by gravity, without the pumping
units. In this case the flow transmitter output
signal pressure will exceed the rate setter output
signal pressure. This condition is sensed by
differential pressure switch "B" which closes its
switch contact whenever the flow transmitter
signal exceeds the rate setter signal by one psi.
31. Differential pressure switch "B" contact then
closes to energize time delay relay TD4, which
must be energized for a period (adjustable from
0.2 to 3 minutes) before its contact closes; hence,
station flow greater than the required set-point
flow for one minute, for example, will.cause
relay TD4 contact to close to pick up time delay
relay TD5.
32. Time delay relay TD5 is one which has
contacts that open immediately when energized
and remain open after being de-energized for an
adjustable period of 0.2 to 3 minutes.
33. The normally closed time delay relay TD5
contacts will then open to de-energize the control
solenoid (1A or 2A) which causes the pump
discharge valve (VI or V2) to close. The purpose
for the delay of the TD5 contacts is to allow
sufficient time for the pump discharge valve to
fully close. This relay should be set for a delay
period slightly greater than the time it takes for
the discharge valve to close.
34. As the discharge valve closes, the differential
switch (IB or 2B) will prevent speed increase to
occur to the point where the differential across
the valve exceeds 10 psi, as explained previously,
should the flow through the station fall below
the set-point flow thus causing the pump speed
controller to try to cause an increase of pump
speed.
35. As the pump discharge valve closes the pump
bypass check gate will commence to open to
allow flow through the throttling gate by gravity.
36. As the pump discharge valve moves in its
closing direction a knee action limit switch
mounted on the valve will momentarily open the
holding circuit of the motor starter as the
discharge valve passes its 95 percent closed
position, to stop the pump motor. The knee
action switch on the valve is adjustable from 90
percent to 97 percent port closure. (The knee
action limit switch on the discharge valve is
normally closed and stays closed while the valve
opens and during valve closure with the
exception of opening momentarily during the
closing stroke at approximately the position of 5
percent valve port opening.
37. As soon as the motor starter is de-energized
auxiliary motor starter contact (Ml or M2) opens
to de-energize solenoid "B" which disconnects
the rate setter signal from the pump speed
controllers, causing the set-point signal pressure
to the pump speed controlers (No. 1 and No. 2)
to drop to exhaust pressure (zero speed signal
pressure). This in turn causes the pump speed
control potentiometers to be returned to zero
speed position.
38. Controller No. 3 is then in control of the rate
of flow through the throttling gate, acting again
as a rate control system for gravity flow through
the station.
39. The station then automatically returns to
pumping if required or continually regulates flow
. through the throttling gate or, if the Eight-Mile
interceptor water level falls to below 0.5 feet a
contact in the Eight-Mile level receiver will open
to break the seal-in circuit on relay R2, thus
de-energizing relay R2.
40. When relay R2 is de-energized, the solenoid
"A" in the station rate setter output signal line is
de-energized, which switches the set-point signal
line to the flow control system to exhaust, (or
zero signal pressure) causing the throttling gate to
close, thus shutting down the station.
41. Anytime during operation, if the Minneola
Treatment Plant wet well level becomes too high,
telemetering level receiver contact STP-1 opens
to de-energize relay R2 to shut down the
regulating station.
Manual Control
Manual control is provided mainly for checking
the individual station components and for control
whenever the Eight-Mile interceptor level
telemetering receiver controller is out of service.
1. Under gravity flow conditions, the throttling
gate may be throttled to any desired position and
stopped and held in that position by means of
the four-position "Automatic-Open-Stop-Close"
manually operated pneumatic selector switch. In
, this case an attendant is required at the station to
maintain the flow within the prescribed limits by
watching the flowmeter. (Any time that the
station is on automatic rate control this selector
switch must be in the "Automatic" position.)
This manual means of control is not necessary for
local control of the station if pneumatic
controller No. 3 is operative, since the controller
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also can be switched to a manual loading station
or set-point signal on the controller.
2. Under gravity flow conditions, if controller
No. 3 is operative, the attendant may switch this
controller from "Automatic" to "Manual" and
adjust the controller output to obtain the desked
flow.
3. If pumping is required, the attendant must
switch the pump motor starter controls from
"Automatic" to "Manual", and switch the pump
speed control to a manually operated speed
control potentiometer. (The speed control
potentiometer should be set at its minimum
speed position before starting the pump.)
4. The pumping unit is started by depressing
the "Start" push-button. This closes the pump
starter circuit and also starts the slip coupling to
operate at the speed determined by the setting of
the manually operated speed control potentiometer
5. The pump starter seals itself through its
auxiliary contact (Ml or M2), the "Stop"
push-button parallel with the valve limit switches,
(VI or V2), and the knee action switches (VI or
V2). (The purpose of parallel limit switches VI
or V2 is to permit stopping the pump motor if,
for some reason, the discharge valve fails to open
during the initial starting period.)
6. When the pump motor starts, the pump
speed must be increased slowly until the pump
discharge pressure is .,5 psi above the station
discharge pressure, to cause the pump discharge
valve to commence to open. The differential
pressure switch (1A. or 2A) senses the 5 psi
differential and energizes the pump discharge
valve control solenoid (1A or 2A) and relay (R5
or R6) to seal the control solenoid circuit to
drive the discharge valve fully open.
7. The attendant must raise the speed of the
pumping unit gradually during the pump
discharge valve opening cycle to prevent the
development of greater than a 10 psi differential
across the discharge valve.
8. If, the pressure across the discharge valve
exceeds 10 psi, the relay (R7 or R8) will pick up
and sound an alarm. (This will notify the
attendant to reduce or at least not to increase
speed until the valve opens farther.)
9. When the discharge valve is fully open, the
speed of the pumping unit is manually controlled
to maintain the flow of the station at the
required stage by watching the flowmeter and
adjusting the manual speed control
potentiometer accordingly.
10. The pumping unit is shut down by depressing
the "Stop" push-button.
11. As the valve begins to close the speed should
be reduced to maintain less than 5 psi differential
across the valve.
12. When the valve is 97 percent closed, the
pump motor will stop.
Alarms and Instruments for
Future Operations Control Center.
1. If relay R4, which actuates the standby
pump, is energized and neither pump is running,
the time delay relay TD6 is energized.
2. If relay R9, which indicates that the station
flow exceeds set-point flow, is energized, the
time delay relay TD6 is energized.
3. Time delay relay TD6, when energized for an
adjustable period of 0.2 to 3 minutes, will close
its contact to transmit an alarm tone via leased
telephone line to the Operations Control Center.
4. The diverted flow rate is telemetered to the
Operations Control Center. The recording
receiver has an alarm contact which closes if the
flow exceeds the contracted allowable limit.
5. As noted on the block diagram, it is planned
that remote rate setting equipment will be
installed in the future. Obviously when this is
done a transfer switch "Local-Remote" should be
installed to allow the use of either the original
local rate setter or the remote rate- setter.
The next step is to simplify the system as much
as possible. This particular problem is an example of
just how complex a system might become by
seemingly relatively simple conditions existing when
determining the design requirements. Limiting the
working pressure across the discharge valves, for
example, has introduced a number of controls,
whereas, the selection of a different type' of .valve
might have significantly simplified the control
scheme. As the design progresses, it behooves the
persons in each professional discipline involved to be
aware of the complications they may be introducing
by their particular design or selection of equipment
and to attempt to simplify the control requirements.
Once the system has been simplified and
established the scaling or calibration of the devices is
necessary. This will involve the selection of the most
suitable ranges for measurement with respect to
control performance. In some cases separate metering
for control is advisable, such as the measurement of
water level. In this instance, one measurement is
advisable for metering of zero to maximum level;
another for. level measurement of the narrow band
over which control is to be exercised.
131
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Another item that must be considered is use of
"live" or "dead" zero output signals from
instruments, as with time-impulse telemetering
equipment. Arguments can be presented for both;
but, for a particular application one will be more
suitable than the other.
The' designer must be concerned with accuracy,
reliability, and maintenance requirements; must
provide for clean, dry air for pneumatic systems as
well as for voltage regulated within prescribed limits,
for electrical circuits, together with over-voltage
protective devices.
Although nothing has been mentioned herein
regarding the telephone lines or communication
facilities, it must be emphasized that regardless of the
degree of excellence of the control system or
equipment, the success or failure of the system will
depend upon the quality and reliability of the
communication facilities.
7.4 Comments
The customer must be extremely careful about
what is required from the control and instrument
designer. Almost any system control problem can be
solved but the cost of implementation and operation
must not outweigh the benefits to the total system.
In the development of an Operation Control
Center, the approach is somewhat similiar to that
mentioned herein for the design of a single station
control scheme. Here the complete picture may be
represented again in block diagram form with each
block representing a certain controlled station,
telephone exchange, and control center, with the
interconnecting lines representing the
communications.channels. The degree of success will
depend almost entirely upon the extent of
understanding that each and every one has about the
whole system and all of its component parts. This
must include management, all of the professional
services involved in design, equipment suppliers,
contractor, and telephone and power utility
personnel.
132
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SECTION 8
ACKNOWLEDGEMENTS
The American Public Works Association is deeply indebted to the following persons and their organizations for the
services they rendered to the APWA Research Foundation in carrying out this study for the 25 local governmental
jurisdictions and the Federal Water Quality Administration who co-sponsored the study. Without their cooperation
and assistance the study would not have been possible. The cooperation of the American Society of Civil
Engineering (ASCE) and the Water Pollution Control Federation (WPCF) is acknowledged for their participation on
the project Steering Committee.
Steering Committee
Arthur D. Caster (WPCF)
William Dobbins (ASCE)
George T. Gray
Carmen Guarino (WPCF)
Walter A. Hurtley
Peter F. Mattel, Chairman
EdSusong
Harvey Wilke (ASCE)
Consultants
Dr. Morris M. Cohn, Consulting Engineer
Ray Lawrence, Black & Veatch, Consulting Engineers
M. D. R. Riddell, Greeley and Hansen, Consulting Engineers
Morris H. Klegerman, Alexander Potter Associates, Consulting Engineers
James J. Anderson, Watermation, Incorporated
Federal Water Quality Administration
Darwin R. Wright, Project Officer
William A. Rosenkranz, Chief, Storm and Combined
Sewer Pollution Control Branch, Division of Applied
Science and Technology.
Manufacturers Advisory Panel
Vernon F. Brown
Peter A. Freeman
R. E. Gerhard
R. W. Henderson
Karl E. Jasper
Louis F. Lemond
Charles Prange
Milton Spiegel, Chairman
Jack D. Stickley
E. P. Webb
Leon W. Weinberger
Badger Meter Manufacturing Co.
Bowles Fluidics Corporation
Allis-Chalmers Company
Rodney Hunt Company
American Chain & Cable Co., Inc.
Coldwell-Wilcox Company
Rockwell Manufacturing Co.
FMC Corporation
Honeywell, Inc. ^
Firestone Coated Fabrics Co.
Zurn Industries, Inc.
133
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ACKNOWLEDGEMENTS (Continued)
Advisory Committee
Vinton Bacon
Donald Bee
Philip Blunck
C. A. Boeke
C. A. Boileau
Ron Bonar
Richard J. Durgin
Paul Ehrenfest
John F. Flaherty
George T. Gray
Allison C. Hayes
Robert S. Hopson
Walter A. Hurtley
Roy L. Jackson
Gene E. Jordan
Robert E. Lawrence
O. H. Manuel
Peter F. Mattei
Hugh McKinley
George J. Moorehead
J. D. Near
Richard W. Respress
Max N. Rhoads
Harry E. Rook
Ben Sosowitz
Ed Susong
The Metropolitan Sanitary District
of Greater Chicago, Illinois
City of Muncie, Indiana
Municipality of Metropolitan
Seattle, Washington
City of Middletown, Ohio
City of Montreal, Quebec, Canada
City of Fort Wayne, Indiana
City of Alexandria, Virginia
City of Cleveland, Ohio
City of Boston, Massachusetts
Allegheny County Sanitary Authority,
Pittsburgh, Pennsylvania
Metropolitan District Commission,
Boston, Massachusetts
City of Richmond, Virginia
City of St. Paul, Minnesota
City of Kansas City, Missouri
City of Omaha, Nebraska
Metropolitan Government
of Nashville & Davidson County
City of Charlottetown, P.E.I., Canada
Metropolitan St. Louis
Sewer District, Missouri
City of Eugene, Oregon
Washington, District of Columbia
City of Toronto, Ontario, Canada
City of Atlanta, Georgia
City of Owensboro, Kentucky
City of Syracuse, New York
The Metropolitan Sanitary District
of Greater Chicago, Illinois
City of Akron, Ohio
134
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r
BIBLIOGRAPHIC: American Public Works Association
Research Foundation. Combined Sewer Regulations and
Management - Manual of Practice FWQA Publication No.
ABSTRACT: Design application operation and maintenance of
combined sewer overflow regulator facilities are detailed in
this Manual of Practice, developed in conjunction with a
report prepared on combined sewer overlfow regulators.
Design calculations are given for various types of regulators
and tide gates. A sample regulator facility control program is
Sven to illustrate the development of a control system.
peration and maintenance guidelines are also given
Thirty-eight sketches and photographs are included.
This manual and accompanying report were submitted in
fulfillmennt of Contract 14-12-456 between the Federal
Water Quality Administration, twenty-five local jurisdictions
and the APWA Research Foundation.
BIBLIOGRAPHIC: American Public Works Association,
Research Foundation. Combiner! Sewer Regulations and
Management - Manual nf Practice FWQA Publication No
11022DMU08/70
ABSTRACT: Design application operation and maintenance of
combined sewer overflow regulator facilities are detailed in
this Manual of Practice, developed in conjunction with a
report prepared on combined sewer overlfow regulators.
Design calculations are given for various types of regulators
and tide gates. A sample regulator facility control program is
given to illustrate the development of a control system.
Operation and maintenance guidelines are also given.
Thirty-eight sketches and photographs are included.
This manual and accompanying report were submitted in
fulfillmennt of Contract 14-12-456 between the Federal
Water Quality Administration, twenty-five local jurisdictions
and the APWA Research Foundation.
KEY WORDS
Combined Sewers
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
KEY WORDS
Combined Sewers
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
BIBLIOGRAPHIC: American Public Works Association,
Research Foundation. Combined Sewer Regulations and
Management - Manual of Practice FWQA Publication No.
11022DMU08/70
ABSTRACT: Design application operation and maintenance of
combined sewer overflow regulator facilities are detailed in
this Manual of Practice, developed in conjunction with a
report prepared on combined sewer overlfow regulators.
Design calculations are given for various types of regulators
and tide gates. A sample regulator facility control program is
given to illustrate the development of a control' system.
Operation and maintenance guidelines are also given.
Thirty-eight sketches and photographs are included.
This manual and accompanying report were submitted in
fulfillmennt of Contract 14-12-456 between the Federal
Water Quality Administration, twenty-five local jurisdictions
and the APWA Research Foundation.
KEY WORDS
Combined Sewers'
Overflows
Regulators
Design
Operation
Maintenance
System Control
Quantity of Overflow
Quality of Overflow
Tide Gates
-------
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1
Access/on Number
5
6
2
Subject
Field & Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization ,
The American Public Works Association, 1313 E. 60th Street
Chicago, Illinois 60637
Title
rr>MT}TMT?n
ot?T.n?T> •DT'mrr ATT/"YNT A-Km TurAiaAr»-cnk*TG'TaT*
10
Authors)
The American Public Works
Association
22
11
Date
June 25, 1970
16
12
Pages
Project Number
APWA 68-01
21
1 j- Contract Number
14-12-456
Note
Citation
23
Descriptors (Starred First)
*0ver£low, *Regulation, design, operations, maintenance
25 Identifiers (Starred First)
*Combined sewers, system control, quantity of overflow, quality of overflow, tide gates
27
Abstract
Design application, operation and maintenance of combined sewer
overflow regulator facilities are detailed in this Manual of Practice, developed
in conjunction with a report prepared on combined sewer overflow regulators.
Design calculations are given for various types of regulators and
tide gates. A sample regulator facility control program is given"-to illustrate.
the development of a control system. Operation and maintenance guidelines are
also given. Thirty-eight sketches and photographs are included.
This manual and accompanying report were submitted in fulfillment
of Contract 14-12-456 between the Federal Water Quality Administration, twenty-five
local jurisdictions and the American Public Works Research Foundation.
Abstractor
Richard H. Sullivan
institution APWA Research Foundation
WR;102
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As the Nation's principal conservation agency, the Department of the
Interior has basic responsibilities for water, fish, wildlife, mineral, land,
park, and recreational resources. Indian and Territorial affairs are other
major concerns of America's "Department of Natural Resources."
The Department works to assure the wisest choice in managing all our
resources so each will make its full contribution to a better United
States—now and in the future.
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