DESIGN CRITERIA
FOR
STAGE I VAPOR CONTROL SYSTEMS
GASOLINE SERVICE STATIONS
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF AIR QUALITY PLANNING AND STANDARDS
EMISSION STANDARDS AND ENGINEERING DIVISION
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
NOVEMBER 1975
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CRITERIA FOR STAGE I SERVICE STATION CONTROL SYSTEMS
Background
Transportation Control Plans (TPC's) promulgated by EPA in 1973
and 1974 include requirements for the control of gasoline vapors at
service stations in some 17 Air Quality Control Regions (AQCR's)
throughout the nation. In all cases, control of gasoline vapors during
storage tank filling (.Stage I sources) is required. In many areas,
control of vehicle fueling (Stage II sources) is also required. For
storage tank filling, EPA regulations prohibit the release of more than
10 percent by weight of displaced organic vaoors.
While Stage I vapor control systems are relatively new, there has
been substantial testing which shows that compliance with prescribed
limits can be accomplished at commerical service stations. Tests by
oil companies, '^' EPA, and a local control agency^ indicate that
efficiencies greater than 90 percent are effected with simple balance
systems- if certain common design elements are employed and if the
equipment is properly maintained and operated. Based primarily on this
testing, criteria have been developed for Stage I control systems.
The purpose of this document is to provide direction to operators
who are required to install vapor recovery systems.
These criteria list the key features of systems which have been
found to meet Stage I requirements. Systems incorporating different
criteria may be installed if test data are supplied to show that they
meet the emission limitation and other provisions of the Stage I
regulations.
All current systems used to control emissions from storgage tank
filling return displaced vapors to the tank truck. Vapor balance
(displacement) systems release any excess vapors to the atmosphere;
vacuum assist systems process excess vapors in secondary recovery
units.
As shown in the vapor balance systems of Figures 1 and 2 and
the secondary system in Figure 3, flexible hoses carry liquid gasoline
from the tank truck down a drop tube to the underground tank. Entering
liquid forces the air-hydrocarbon mixture in the tank out through a
flexible hose to the tank truck. Alternately, the vapors may exit from
the underground tank through a vent pipe (about 2 inches in diameter)
extending at least 12 feet above ground level (OSHA and National Fire
Protection Code 30 requirement). At the truck, the vapor hose is
connected to a piping manifold which may serve as a rollover rail to
prevent damage to the tank in case the truck is overturned. The roll-
over rail piping is interconnected with the truck compartments by vents
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which are opened selectively durinq truck unloadinq, allowina returnina
vapors from the underground tank to enter respective product compartments
on the truck.
Two-Point Systems
The most effective method of conductinq displaced vapors from the
underqround tank to the truck is by means of a separate connection to
the underground tank for the 3-inch vapor return hose, as shown in
Figure 1. The vast majority of the tests showina comoliance with
prescribed limits are from systems utilizinq this feature.
Concentric or Coaxial Systems
However, in some cases a separate entry is not available or the
operator desires to avoid the excavation necessary to reach an unused
entry. For these cases, coaxial devices have been developed to remove
the vapors through the same opening through which the fuel is delivered.
In one system, shown in Figure 4, a droo tube of smaller diameter
is inserted in the existing fuel riser. The vaqors exit through the
annular space. A coaxial adaptor fits on the riser and provides
connections for the fuel delivery hose and the vapor return hose.
In another system, shown in Figure 5, the fuel and vapor passages
are separated in a "Y" fitting which is permanently attached to the
underground tank/" The fittings for the hose connections are located
in a conventional manhole. A 5-inch coaxial fitting is shown in Figure 7.
Most of these devices provides less cross-sectional area in the vapor
return passaqe than do' separate connectors and tend to reduce vapor
recovery efficiency to some extent. Vent pipe restrictions will improve
efficiencies.
Manifolded Vent Lines
Several schemes have been used to manifold vents from two or more
tanks- to a common vapor hose connection, ^anifoldinq may be above or
below grade. A number of configurations are acceptable for use with
suitable vent restrictions as shown in Figure 8. The 3-way connector
of Fiaure ? provides the most effective arranaement since connection
of the vapor hose to the common connector blocks flow to the atmosphere
and routes all displaced vapor to the tank truck. In any manifold piping
system, care must be exercised to prevent contamination of "no-lead"
gasoline product.
Objectives of Design Criteria
Design criteria presently included in this document pertain primarily
to commercial stations where filling conditions are most severe. Here
there are usually two or three storage tanks, each of which ranqe UP to
10,000 gallons in capacity. They are normally filled from a tank truck
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of about 4,000-gallon capacity if a sinqle tanker or 8,000-qallon capacity
if a trailer is added. Each truck and trailer is compartmented such that
different grades of gasoline can be transported without comingling.
Normal practice at commercial stations is to fill storaqe tanks at
a rate of 200 to 500 gallons oer minute. Thus, a typical 4,000-aallon
droo may be accomplished in 10 to 20 minutes. The drop rate is critical
since it governs the rate of vapor transfer. Where slower fill rates are
used, ft may be possible to use smaller transfer hoses and connections.
Also, leakage at storage tanks and tank trucks tends to be of lesser
magnitude at slower filling rates.
Criteria were developed to accomplish the following:
assure submerged fill, i.e., discharge liquid below
the gasoline surface in the storaqe tank,
(b) assure that the vapor return line and connections
are of sufficient size and sufficiently free of restrictions
to allow transfer of vapor to the truck tank and achieve
the desired recovery,
(cj assure that there are no significant leaks in the
system or the tank truck which reduce vacuum in the truck
or otherwise inhibit vapor transfer,
Cd) assure that the vapor return line will be connected
during tank, filling.
In addition, cognizance has been taken of safety requirements of
the Occupational Safety and Health Administration (OSHA)' and the
recommendations of the National Fire Protection Association.
Design Criteria
1. Drop Tube Specifications. Submerged fill is specifically required
By certain TCP regulations wn.il a others are silent on the method of
filling. All test data submitted to EPA were obtained from systems
utilizing submerged fill. If submerged fill is not used, test data
must be submitted to show the required recovery will be obtained.
The submerged fill requirement is interpreted to mean a drop tube
extendfnq to within 6 inches of the tank bottom. Under normal industry
practices, a tube meeting this specification will always be submerged
sines the tanks are not pumped dry.
Deviation from the criteria will be allowed if the owner/operator
shows that a shorter tube will guarantee sufamerqed fill. In such
instance, the owner/operator is required to present records which show
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that the level in the tank never falls below the drop tube. Exceptions
also will be allowed for tanks which cannot be converted to submerged
fill, e.g., tanks with offset fill lines or ooor accessibility.
2. Gauoe Wei 1. If a gauge well separate from the fill tube is used,
it must be provided with a drop tube which extends to within 6 inches
of the tank bottom. This will prevent vapor emissions in case the gauge
well cap is not replaced during a drop.
3. Vapor Hose Return. Existing data indicate that a 3-inch ID hose
is needed to transfer vapors from the storage tank to the truck when a
4-inch drop tube is used. Smaller diameter hoses may be satisfactory
where fill rates are appreciably less than 400 aallons per minute.
If a hose smaller than 3 inches is to be used, the owner/operator is
required to show that the hose will achieve the required vapor recovery.
4. Vapor Line Connections. Where separate vapor lines are used with
4-inch product tubes, nominal 3-inch or larger connections should be
utilized at the storage tank and truck-trailer. When smaller product
tubes are used, a smaller vapor line connection may be used, provided the
ratio of the cross-sectional area of the connection to the cross-sectional
area of the product tube is 1:2 or greater. If the ratio is smaller, test
data must be provided to show the required recovery efficiency will be met.
Vapor lines from two or more tanks may be manifolded to a common
vapor hose connector using configurations typified by Figures 8 and 9.
For concentric or other tube-in-tube fittings, operatina characteristics
are uniaue to the particular design. To date, adequate test data have been
supplied for 4-inch and 5-inch tube-in-tube adapters. These are listed
in Attachment A. Other fittings will be added to Attachment A when supporting
data are supplied. If fittinas not listed are to be used, test data must
Be provided.
5". Type of Liquid Fill Connection. Vapor tight caps are required for the
liquid fill connection for all systems. A positive closure utilizing a
gasket or other similar sealino surface is necessary to prevent vaoors from
being emitted at around level. Cam-lock closures meet this requirement.
Dry-breafc closures also are acceptable, but are not required.
5". Tank Truck^Inspection. Vapor tiaht tank trucks are specifically required
by TCP regulations-, fhis is interpreted to mean that the truck compartments
won^t vent gases or draw in air unless the settings of the pressure-vacuum
relief valves are exceeded. An inspection procedure should be submitted to
include freouent visual inspection and leak testing at least twice per year.
Leak testing should demonstrate that the tank truck when pressurized to
5 inches W.C. will not leak to a pressure of 2 inches W.C. in less than
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3 minutes. Frequent visual inspection is necessary to insure proper
operation of manifolding and relief valves.
7. Closures or ^Interlocks on Underground Tank Vapor Hose Connectors.
Closures or interlocks are required to assure transfer of displaced vapors
to the truck and to prevent ground level gasoline vapor emissions due to
failure to connect the vapor return line to the underground tanks.
These devices must be designed: (a) to keep the storage tank sealed
unless the vapor hose is connected to it; or (b) to prevent delivery of
fuel until the vapor hose is connected, i.e., an interlock. Tank openings
designed for combined fill and vapor recover shall also be protected against
vapor release unless connection of the liquid delivery line to the fill
pipe simultaneously connects the vapor recovery line, e.g., an interlock.
All connections must be vapor tight.
8. Vaoor Hose Connection to the Tank Truck. A means must be provided
to assure that tne vapor hose is connected to the truck before fuel is
delivered. Acceptable means of providing this assurance include:
(a) permanent connection of the vapor hose to the truck; (b) an inter-
lock which prevents fuel delivery unless the vapor hose is connected,
such as a bracket to which the product and vapor hose are permanently
attached so that neither hose can be connected separately; and (c) a
closure in the vapor hose which remains closed unless the hose is
attached to the vapor fitting on the truck.
9. Vent Line Restrictions. Vent line restrictions improve recovery
efficiency and provide assurance that the vapor return line will be
connected durfng transfer. If the liquid fill line were attached to
the underground tank and the vapor return line disconnected, closures
would seal the vapor return path to the truck forcing all vapors out
the vent line. Restriction of the vent line through the use of an
orifice or pressure-relief valve greatly reduces fill rate in such
instances warning the operator that the vapor line is not connected.
Suitable restrictive orifices or pressure-relief valves are required
wherever the systems would otherwise be incapable of achieving 90 percent
control or would otherwise not assure that the vapor return line is
connected. For available hardware this means that these restrictive devices
are necessary for all except systems with interlock connections at both
the truck and storage tank.
Either of the following restrictive devices are acceptable:
Ca) Orifice of 1/2 to 3/4 inch ID.
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(b) Pressure-vacuum relief valve set to open at 8 oz. per
square inch or greater pressure and 4 02. per square inch
or greater vacuum. The vacuum relief feature of a P-V valve
is not required for Stage I recovery purposes but may be
required by safety authorities.
The NFPA Interim Amendments (April 1975) to Code 30 require that when
vent restriction devices are used the tank and associated piping be
protected to limit back pressure development to less than the maximum
working pressure of the tank and equipment by the provision of pressure
vacuum vents, rupture discs or other tank venting devices installed in the
tank vent lines, and that these devices shall be protected to minimize the
possibility of blockage from weather, dirt, or insect nests. Local fire
marshals should be consulted regarding the use of these devices in your
area.
References
1. Performance of Service Station Vapor Control Concepts, Scott
Research Laboratories for the American Petroleum Institute, Interim
Report, June 26, 1974.
2. Service Station Vapor Recovery, Atlantic-Richfield Company,
April 8, 1974,
/
3. Presten, J. E. et al, The "Displacement" System: An Effective
Method of Controlling Hydrocarbons, November 1973.
4. TRW Contract Test,. June 1974, San Diego, California.
5. Bay Area Air Pollution Control District, 1974.
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Comparcnenc
Venc Valves
Orifice or P-V Valve
Unless Product and
Vapor Hoses are
Interlocked.
Orybreak,
interlock or
Permanent
Connection
Figure 1.
Vapor balancing with
separate liquid - vapor
risers.
Coapartaenc
VenC Valves
Orifice or P-V Valve
Unless Product and -^.
Vapor Hoses are
Interlocked.
U. Q. Tank _
Vent Pipe
(usually 2")
Oryoreak,
interlock or
Permanent
tions
Co-Axial
Slbow
Connection
Vapor Return
Hose (3" ID)
Figure 2.
Vapor balancing with single,
concentric liquid - vapor
riser.
Compartaanc
Vent Valves
P-V Valve -
Figure 3. Secondary recovery with
separate liquid - vapor
risers.
Secondary
Processing
Unit
Orybreak,
Interlock or
Permanent
ns
Vapor Return
Hose (3" ID)
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Figure 4. Coaxial Fittin;
and Fill Tube Adapter.
Emco Wheaton Inc.
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NEW OPW 306-AO-12" x 24" MANHOLE
EXISTING CAP AND ADAPTOR
OR
NEW OPW S34-TT-4" CAP
AND
633-T-4" x 4" ADAPTOR
OR
62-TT-4" CAP OR 52-4" CAP
AND
61-AS-4" x 4" ADAPTOR
NEW OPW 313-V-4" x 4" x 3"
"Y" FITTING
NEW OPW 61-TD-4" x lO'-O"
DROP PIPE
Of
VAPOR AREA
OPW 1711-TK-3" CAP
OR
OPW 1711-KV-3"
CAP
OPW 1611-AV-3"
ADAPTOR
EXISTING UNDERGROUND STORAGE TANK
4 P/PE
Figure 5. "Y" Tube-
Tube Vapor Return F
Dover Corporation/01
Division
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ft*.
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fittgliilK ^-j«|||?
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Figure 6. Coaxial Fitting for 6" Riser Pipes.
Parker Hannifin, Inc.
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Closes when vapor hose
is attached.
Vapor Line
Product Line
Figure 9. Aboveground Manifolding of Vapor Lines
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Attachment A*
(Revised November 1975)
Concentric and tube-in-tube couplers for which test data show acceptable
performance:
1. Emco Wheaton 4-inch Coaxial Fitting F-278, adapter and Drop
Tube Assembly A70-001.
2. Emco Wheaton 4-Inch Coaxial Fitting F-278. Adapter with a
4-inch to 3-inch bushing and Drop Tube Assembly A70-003.
3. Dover Corporation/OPW Division 4-inch Tube-In-Tube Y-Fitting
No. 318 with 61-TD-4 Inch Drop Pipe.
4. Parker Hannifin 6-inch Coaxial Fitting F-219 with a 6-inch
Straight Riser or a 6-inch by 4-inch Riser.
5. Universal Valve 4-inch Fill/Vapor Return Fitting No. 715.
*This attachment has no relation to "two point" systems, i.e., systems
with a separate connection for the vapor return hose to the underground
tank. Such systems are to be evaluated by the Criteria.
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