United States
                        Environmental Protection
                        Agency
 Office of Water
 Washington, D.C.
EPA 832-F-00-071
September 2000
                        Wastewater
                        Technology  Fact  Sheet
                        Sewers,  Force  Main
DESCRIPTION

Force mains are pipelines that convey wastewater
under pressure from the discharge side of a pump or
pneumatic ejector to a discharge point. Pumps or
compressors located in a lift station provide  the
energy for wastewater conveyance in force mains.
The key elements offeree mains are:

1.     Pipe.

2.     Valves.

3.     Pressure surge control devices.

4.     Force main cleaning system.

Force mains are constructed from various materials
and come in a wide range of diameters. Wastewater
quality  governs the selection of the most suitable
pipe  material.  Operating pressure  and corrosion
resistance also impact the choice. Pipeline size and
wall thickness are determined by wastewater flow,
operating pressure, and trench conditions.

Common Modifications

Force mains  may be aerated or the wastewater
chlorinated at the pump station to prevent odors and
excessive corrosion. Pressure surge control devices
are installed to reduce pipeline  pressure below a
safe operating pressure during lift station start-up
and shut-off.  Typically, automatically operated
valves (cone or ball type) control pressure surges at
the pump discharge  or pressure  surge tanks.
Normally, force main cleaning includes running a
manufactured "pigging" device through the line and
long force mains are typically equipped with "pig"
insertion and retrieval stations.  In most cases,
insertion facilities are located within the lift station
and the pig removal station is at the discharge point
of the force main. Several launching and retrieval
stations are usually provided in long force mains to
facilitate cleaning of the pipeline.

APPLICABILITY

Force mains are used to convey wastewater from a
lower to higher elevation, particularly where the
elevation of the source is not sufficient for gravity
flow and/or the use of gravity conveyance will
result in excessive  excavation  depths and high
sewer pipeline construction costs.

Ductile iron and polyvinyl chloride (PVC) are the
most frequently used materials for wastewater force
mains. Ductile iron pipe has particular advantages
in wastewater collection systems due to  its high
strength  and high flow capacity with greater than
nominal inside diameters and tight joints.  For
special  corrosive conditions and extremely high
flow characteristics, polyethylene-lined ductile iron
pipe and fittings are widely used.

Cast iron pipe with glass lining is available in
standard pipe sizes, with most joints in lengths up
to 6.1 meters (20 feet). Corrosion-resistant plastic
lined piping systems are  used for certain waste
carrying applications. Polyethylene-lined ductile
iron pipe and fittings known as "poly-bond-lined"
pipe  is widely used for force  mains conveying
highly corrosive industrial or municipal wastewater.

The types of thermoplastic pipe materials used for
force  main  service  are PVC,  acrylonitrile-
butadiene-styrene (ABS),  and polyethylene (PE).

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The  corrosion resistance, light weight, and  low
hydraulic friction characteristics of these materials
offer certain advantages  for different force main
applications,  including  resistance  to microbial
attack.  Typically, PVC pipes  are  available in
standard diameters of 100 to 900 mm (4 to 36
inches) and their  laying lengths  normally range
from 3  to 6 meters (10  to 20 feet).   The use of
composite  material  pipes,  such as  fiberglass
reinforced mortar pipe ("truss pipe"), is increasing
in the construction offeree mains. A truss pipe is
constructed  on  concentric ABS cylinders  with
annular space filled with cement. Pipe fabricated of
fiberglass reinforced epoxy resin is almost as strong
as steel, as well as corrosion and abrasion resistant.

Certain  types  of  asbestos-cement  pipe  are
applicable  in  construction of  wastewater force
mains.  The advantage of asbestos-cement pipes in
sewer applications is their low hydraulic friction.
These  pipes are relatively lightweight, allowing
long laying lengths in long lines. Asbestos-cement
pipes are also  highly  corrosion resistant.  At one
time it was thought that many asbestos containing
products (including asbestos-cement pipe) would be
banned by the Environmental Protection Agency.
However, a court ruling overturned this ban and this
pipe is available and still used for wastewater force
main applications (Sanks, 1998).

Force  mains  are  very  reliable  when they are
properly designed and maintained. In general, force
main reliability and useful life are comparable to
that  of gravity sewer lines, but pipeline reliability
may be compromised by excessive pressure surges,
corrosion, or lack of routine maintenance.

ADVANTAGES AND DISADVANTAGES

Advantages

Use offeree mains can significantly reduce the size
and depth of sewer lines and decrease the overall
costs of sewer system construction.  Typically,
when gravity sewers are installed in trenches deeper
than 6.1 meters  (20 feet), the cost of sewer line
installation increases  significantly because more
complex and  costly  excavation  equipment  and
trench shoring techniques are required. Usually, the
diameter of pressurized force mains is one to two
sizes  smaller than the diameter of gravity sewer
lines conveying the same flow, allowing significant
pipeline cost reduction.  Force main installation is
simple because of shallower pipeline trenches and
reduced quantity of earthwork. Installation offeree
mains is not dependent on site specific topographic
conditions and is not impacted by available terrain
slope, which typically limits gravity wastewater
conveyance.

Disadvantages

While construction offeree mains is less expensive
than gravity sewer lines for the same flow, force
main  wastewater   conveyance  requires  the
construction and operation of one  or more lift
stations.  Wastewater pumping  and  use of force
mains could be eliminated or reduced by selecting
alternative sewer routes, consolidating a proposed
lift station with an existing lift station, or extending
a gravity sewer using directional drilling or other
state-of-the art deep excavation  methods.

The dissolved oxygen content of the wastewater is
often depleted in the wet-well of the lift station, and
its subsequent  passage through the  force main
results in the discharge of septic wastewater, which
not only lacks  oxygen but often contains sulfides.
Frequent cleaning and maintenance offeree mains
is required to remove solids and grease buildup and
minimize corrosion due to the high concentration of
sulfides.

Pressure  surges  are abrupt increases in operating
pressure  in force  mains  which typically  occur
during pump start-up and shut-off Pressure surges
may have negative effects on force main integrity
but can be reduced by proper  pump station  and
pipeline design.

DESIGN CRITERIA

Force main design is typically integrated with lift
station design. The major factors  to consider in
analyzing force main materials and hydraulics
include the design  formula for sizing the pipe,
friction losses, pressure surges, and maintenance.
The Hazen-Williams formula is recommended for
the design offeree mains.  This formula includes a
roughness  coefficient  C, which  accounts  for

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pipeline hydraulic friction characteristics.   The
roughness  coefficient varies  with pipe material,
size, and age.

Force Main Pipe Materials

Selection criteria for force main  pipe materials
include:

1.      Wastewater quantity, quality, and pressure.

2.      Pipe properties, such  as strength,  ease  of
       handling, and corrosion resistance.

3.      Availability  of  appropriate  sizes,  wall
       thickness, and fittings.

4.      Hydraulic friction characteristics

5.      Cost.

Ductile iron pipe offers strength, stiffness, ductility,
and a range of sizes and thicknesses  and is the
typical  choice  for high-pressure and exposed
piping.  Plastic  pipe is most widely used in  short
force mains and smaller diameters. Table 1  lists the
types of pipe recommended for use in a force main
system and suggested applications.
                              Velocity

                              Force  mains  from the  lift  station are typically
                              designed for velocities between 0.6 to 2.4 meters
                              per second (2 to 8 feet per second). Such velocities
                              are normally based on the most economical pipe
                              diameters and typical available heads.  For shorter
                              force mains (less than 610 meters or 2,000 feet) and
                              low lift requirements  (less than 9.1 meters or 30
                              feet), the recommended design force main velocity
                              range is 1.8 to 2.7 meters per second (6 to 9 feet per
                              second). This higher design velocity allows the use
                              of  smaller  pipe,  reducing  construction  costs.
                              Higher velocity also increases pipeline friction loss
                              by  more than  50 percent, resulting in increased
                              energy costs. To reduce the velocity, a reducer pipe
                              or a pipe valve can be used.  Reducer pipes are
                              often used because  of the  costly nature of pipe
                              valves.  These reducer pipes, which are larger  in
                              diameter, help to disperse   the  flow,  therefore
                              reducing the velocity.

                              The maximum  force  main velocity  at  peak
                              conditions is recommended not to exceed 3 meters
                              per second (10 feet per second).  Table 2 provides
                              examples of force  main capacities  at various
                              pipeline sizes, materials, and velocities.  The flow
                              volumes may vary depending on the pipe material
                              used.
       TABLE 1 CHARACTERISTICS OF COMMON FORCE MAIN PIPE MATERIALS
  Material
Application
Key Advantages
Key Disadvantages
 Cast or Ductile Iron,
 Cement Lined
 Steel, Cement Lined
 Asbestos Cement
  Fiberglass Reinforced
  Epoxy Pipe
  Plastic
High pressure
Available sizes of 4-54 inches
High pressure
All pipe sizes
Moderate pressure
For 36-inch + pipe sizes
Moderate pressure
For up to 36-inch pipe sizes
Low pressure
For up to 36-inch pipe sizes
Good resistance to pressure
surges
Excellent resistance to
pressure surges
No corrosion
Slow grease buildup
No corrosion
Slow grease buildup
No corrosion
Slow grease buildup	
More expensive than
concrete and fiberglass
More expensive than
concrete and fiberglass
Relatively brittle
350 psi max pressure

Suitable for small pipe sizes
and low pressure only	
 Source: Sanks, 1998.

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                             TABLE 2 FORCE MAIN CAPACITY
Diameter
(inches)
6
8
10
18
24
36
Velocity
gpm
176
313
490
1,585
2,819
6,342
= 2fps
Ips
11
20
31
100
178
400
Velocity
gpm
362
626
980
3,170
5,638
12,684
= 4fps
Ips
22
40
62
200
356
800
Velocity
gpm
528
626
1,470
4,755
8,457
19,026
= 6fps
Ips
33
60
93
300
534
1,200
       Source: Metcalf and Eddy, 1981.

Vertical Alignment

Force mains should be designed so that they are
always full and pressure in the pipe is greater than
69 kiloPascals (10 pounds per  square  inch) to
prevent the release of gases. Low and high points
in the  vertical  alignment should be  avoided;
considerable effort and  expense are justified to
maintain an uphill slope from the lift station to the
discharge point. High points in force mains trap air,
which  reduces available  pipe  area, causes non-
uniform flow,  and creates the potential for sulfide
corrosion. Gas relief and vacuum valves  are often
installed if high points in  the alignment of force
mains  cannot  be  avoided, while blowoffs are
installed at low points.

Pressure Surges

The  possibility  of sudden changes  in  pressure
(pressure surges) in the force main  due to starting
and/or stopping pumps  (or operation of  valves
appurtenant to  a pump) must be considered  during
design.   The  duration of such  pressure  surges
ranges between 2 to 15 seconds. Each surge is site
specific and depends on  pipeline  profile,  flow,
change  in  velocity,  inertia  of  the   pumping
equipment, valve characteristics, pipeline materials,
and pipeline accessories.   Critical surges may be
caused by  power failure.  If pressure surge is a
concern, the force main  should be  designed to
withstand calculated maximum surge pressures.
Valves

Valves are installed to regulate wastewater flow and
pressure in the force mains.  Valves can be used to
stop and start flow, control the flow rate, divert the
flow, prevent backflow, and control and relieve the
pressure. The  number, type, and location of force
main valves depends on the operating pressures and
potential surge conditions in the pipeline. Although
valves have a lot of benefits, the costliness of them
prevents them  from being used extensively.

PERFORMANCE

Force main  performance is closely tied to the
performance of the lift station to which  it is
connected.  Pump-force main performance curves
are used to define  and  compare  the  operating
characteristics  of a  given pump or set  of pumps
along with the associated force main. They are also
used  to  identify  the  best  combination  of
performance characteristics under  which  the lift
station-force main system will operate under typical
conditions  (flows  and  pressures).   Properly
designed pump-force main systems usually allow
the lift station pumps to operate at 35 to 55 percent
efficiency most  of the  time.    Overall  pump
efficiency depends  on the  type of pumps,  their
control system, and  the fluctuation  of the influent
wastewater flow.

OPERATION AND MAINTENANCE

The operation  offeree main-lift station systems is
usually automated and does not require continuous
on-site operator presence. However, annual force

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main route inspections are recommended to ensure
normal  functioning  and  to  identify potential
problems.

Special  attention is given to the integrity of the
force  main surface  and  pipeline  connections,
unusual noise, vibration, pipe and pipe joint leakage
and  displacement,  valving  arrangement  and
leakage, lift station  operation and  performance,
discharge pump rates and pump speed, and pump
suction and discharge pressures.  Depending on the
overall performance of the lift station-force main
system,  the extent of grease build-up and the need
for pipeline pigging are also assessed.

If there  is an excessive increase in pump head and
the headloss increase is caused by grease build-up,
the pipeline is pigged.   Corrosion is rarely a
problem since pipes  are primarily constructed of
ductile iron or plastic, which are highly resistant to
corrosion. Buildup can be removed by pigging the
pipeline.

COSTS

Force main costs depend on many factors including:

1.      Conveyed wastewater quantity and quality.

2.      Force main length.

3.      Operating pressure.

4.      Soil properties and underground conditions.

5.      Pipeline trench depth.

6.      Appurtenances   such  as   valves   and
       blowoffs.

7.      Community impacts.

These site and system specific factors must be
examined and incorporated in the preparation of
force main cost estimates.

Construction Costs

Unit force main  construction costs are  usually
expressed in $ per linear foot of installed pipeline
and costs typically include labor and the equipment
and materials required  for pipeline  installation.
Table 3 unit pipeline construction costs for ductile
iron and plastic (PVC) pipes used for force main
construction.  These costs are base installation costs
and do not include the following:

1.      General contractor overhead and profit.

2.      Engineering and construction management.

3.      Land or right-of-way acquisition.

4.      Legal, fiscal, and administrative costs.

5.      Interest during construction.

6.      Community impacts.

All unit pipeline costs are adjusted to 1999 dollars.
  TABLE 3 CONSTRUCTION COSTS FOR
   DUCTILE IRON AND PLASTIC PIPES
Pipe
Diameter
(inches)
8
10
12
14
16
18
20
24
30
36
Ductile Iron
Pipe
($/linear foot)
23
29
36
46
53
66
72
84
142
190
PVC Pressure
Pipe
($/linear foot)
15
20
26
33
41
48
56
65
90
135
 Source: James M. Montgomery Consulting Engineers,
 1998.
Operation and Maintenance Costs

Force  main  operation  and  maintenance  costs
include labor  and  maintenance  requirements.
Typically, labor costs account for 85 to 95 percent
of total operation and maintenance costs and are
dependent  on  the  force  main  length.    The

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maintenance  costs  usually  vary  from  $7  to
$20/meter ($2 to $6/linear foot), depending on the
size and number of appurtenances installed on the
force  main.   An  internal  inspection  using  TV
equipment can be completed, if visual inspection is
not sufficient. TV inspection can be costly, ranging
from $1,000 to $11,450 per mile with an average
cost of $4,600 per mile (WERF,  1997; Arbour and
Kerri, 1997).

Table 4 summarizes force main construction costs
Other EPA  Fact  Sheets  can be  found  at  the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm

1.     Arbour, R.  and K. Kerri, 1997. Collection
      Systems: Methods for  Evaluating and
      Improving Performance. Prepared for the
      EPA Office of Wastewater Management by
      the California State University, Sacramento,
      CA.
          TABLE 4 FORCE MAIN
         CONSTRUCTION COSTS
Project/
Location
Compton,
CA
Oceanside,
CA
Eugene,
OR
CMCWD 1,
CA
CMCWD II,
CA
Goleta, CA
Gillette,
WY
Force Main
Average
Capacity (mgd)
8
18
12
42
30
56
30
Construction
Costs
($US/linear foot)
70
85
90
510
260
365
120
 Source: James M. Montgomery Consulting Engineers,
 1998.

from several projects, adjusted to 1999 dollars.
REFERENCES

Other Related Fact Sheets

Sewers, Lift Stations
EPA 832-F-00-073
September 2000

Pipe Construction and Materials
EPA 832-F-00-068
September 2000

Sewer Cleaning and Inspection
EPA832-F-99-031
September 1999
2.     Bethany R.  B.  May  1994.  Pressure
      Reducing Stations - A Key to Networked
      Interceptor System Operations. Operations
      Forum, Vol. 11, No. 5,8-12.

3.     Casada,  Don.   May    1998.   Pump
      Optimization for   Changing  Needs.
      Operations Forum. Vol. 9, No. 5, 14-18.

4.     Huges D. M. and R.G. Cornforth.  May
      1997. The Importance of Surge Protection
      in  Avoiding  Pump  Station  Failures.
      Operations Forum, Vol. 14, No. 5, 25-28.

5.     Horton A.  M. October 1996. Protective
      Linings for Ductile Iron Pipe in Wastewater
      Service.   In Proceedings of the Water
      Environment Federation.    69th  Annual
      Conference & Exposition, Dallas, Texas,
      Vol. 3.

6.     Jackson J. K. May 1996.  Variable Speed
      Pumping  Brings  Efficiency  to  Pump
      Systems. Operations Forum, Vol. 13, No. 5,
      21-24.

7.     James   M.   Montgomery   Consulting
      Engineers,   1988.    "Sewerage  System
      Preliminary Cost Estimating Curves."

8.     Metcalf & Eddy Inc., 1981. Wastewater
      Engineering: Collection and Pumping of
      Wastewater, McGraw Hill Book Company.

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9.     Moody  T.  C.  October 1998.  Optimizing
      Force  Main  Odor   Control  Chemical
      Dosage: A Tale  of Two Systems. In
      Proceedings of the Water Environment
      Federation,  71st   Annual  Conference,
      Orlando, Florida, Vol. 2.

10.    Paschke N.W. May 1997. Pump Station
      Basics  - Design  Considerations for a
      Reliable Pump Station. Operations Forum,
      Vol. 14, No. 5  15-20.

11.    Prasuhn, A.L.  1987. Fundamentals of
      Hydraulic Engineering, Holt, Rinehart and
      Winston, New York.

12.    Robinson,  P.  E.,  Aguiar  G.,  Grant M.
      October  1995. Fast Tracking the Critical
      Dade County Cross Bay Transmission Line.
      In Proceedings of the Water Environment
      Federation.  68th  Annual  Conference &
      Exposition, Miami Beach, Florida, Vol. 3.

13.    SanksR. L., TchobanoglousG.,NewtonD.,
      Bosserman, B.E., Jones, G. M. 1998. Pump
      Station Design, Butterworths, Boston.

14.    Seigal  S.E.  May  1994. Upgraded to the
      World's  Largest.    Dry-Pit/Submerged
      Pumps Make the Grade. Operations Forum,
      Vol. 11, No. 5,24-28.

15.    Smith E. C. July  1994. Don't  Lose the
      Pump   Efficiency  Game.  Operations
      Forum,Vol.  11, No. 7, 18-21.

16.    U.S. Environmental  Protection Agency.
      October 1985.  Design Manual.  Odor and
      Corrosion  Control in  Sanitary Sewerage
      Systems and Treatment Plants. EPA/625/1 -
      85/018.

17.    Water   Environment   Federation.  1994.
      Existing   Sewer  Evaluation   and
      Rehabilitation.  Manual of Practice No.
      FD6.
18.   Water  Environment  Federation.   1985.
      Operations and Maintenance ofWastewater
      Collection Systems.   Manual of Practice
      No. 7.

19.   Water  Environment  Federation.   1992.
      Wastewater  Collection   Systems
      Management. Manual of Practice No. 7.

20.   Water Environment Research Federation
      (WERF), 1997. Benchmarking Wastewate
      Operations - Collection,  Treatment, and
      BiosolidsManagement. Project 96-CTS-5.

21.   Workman G., and M.D. Johnson. October
      1994.  Automation  Takes Lift Station  to
      New Heights. Operations Forum, Vol. 11,
      No. 10, 14-16.

ADDITIONAL INFORMATION

Luis Aguiar, Assistant-Director
Miami-Bade Water and Sewer Department
4200 Salzedo Street
Coral Gables, FL 33146

Eileen M. White
East Bay Municipal Utility District
P.O. Box 24055
Oakland, CA 94523

Richard  R. Roll
Wastewater Treatment Plant
P.O. Box 69
Niagara  Falls, NY 14302

Gary N.  Oradat
City of Houston DPW& Engineering
Utility Maintenance Division
306 McGowen Street
Houston, TX 7706

David Jurgens
City of Fayetteville
113 West Mountain Street
Fayetteville, AR 72701

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Bruno Conegliano
Water & Wastewater Utility
City of Austin, P.O. Box 1088
Austin, TX 78767

The  mention of trade  names  or  commercial
products  does not  constitute  endorsement or
recommendations for use by the United States
Environmental Protection Agency (EPA).
                                                         For more information contact:

                                                         Municipal Technology Branch
                                                         U.S. EPA
                                                         Mail Code 4204
                                                         1200 Pennsylvania Avenue, NW
                                                         Washington, D.C. 20460
                                                          MTB
                                                         Excellence fri compliance through optimal technical solutions
                                                         MUNICIPAL TECHNOLOGY BRANCH

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