Method 27 8/3/2017

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METHOD 27 - DETERMINATION OF VAPOR TIGHTNESS OF GASOLINE

1.0 Scope and Application

1.1 Applicability. This method is applicable for the determination of vapor tightness of a
gasoline delivery collection equipment.

2.0 Summary of Method

2.1 Pressure and vacuum are applied alternately to the compartments of a gasoline delivery tank
and the change in pressure or vacuum is recorded after a specified period of time.

3.0 Definitions

3.1 Allowable pressure change (Δp) means the allowable amount of decrease in pressure during
the static pressure test, within the time period t, as specified in the appropriate regulation, in mm
H2O.

3.2 Allowable vacuum change (Δv) means the allowable amount of decrease in vacuum during
the static vacuum test, within the time period t, as specified in the appropriate regulation, in mm
H2O.

3.3 Compartment means a liquid-tight division of a delivery tank.

3.4 Delivery tank means a container, including associated pipes and fittings, that is attached to
or forms a part of any truck, trailer, or railcar used for the transport of gasoline.

3.5 Delivery tank vapor collection equipment means any piping, hoses, and devices on the
delivery tank used to collect and route gasoline vapors either from the tank to a bulk terminal
vapor control system or from a bulk plant or service station into the tank.

3.6 Gasoline means a petroleum distillate or petroleum distillate/alcohol blend having a Reid
vapor pressure of 27.6 kilopascals or greater which is used as a fuel for internal combustion
engines.

3.7 Initial pressure (Pi) means the pressure applied to the delivery tank at the beginning of the
static pressure test, as specified in the appropriate regulation, in mm H2O.

3.8 Initial vacuum (Vi) means the vacuum applied to the delivery tank at the beginning of the
static vacuum test, as specified in the appropriate regulation, in mm H2O.

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3.9 Time period of the pressure or vacuum test (t) means the time period of the test, as specified
in the appropriate regulation, during which the change in pressure or vacuum is monitored, in
minutes.

4.0 Interferences[Reserved]

5.0 Safety

5.1 Gasoline contains several volatile organic compounds (e.g., benzene and hexane) which
presents a potential for fire and/or explosions. It is advisable to take appropriate precautions
when testing a gasoline vessel's vapor tightness, such as refraining from smoking and using
explosion-proof equipment.

5.2 This method may involve hazardous materials, operations, and equipment. This test method
may not address all of the safety problems associated with its use. It is the responsibility of the
user of this test method to establish appropriate safety and health practices and determine the
applicability of regulatory limitations prior to performing this test method

6.0 Equipment and Supplies

The following equipment and supplies are required for testing:

6.1 Pressure Source. Pump or compressed gas cylinder of air or inert gas sufficient to pressurize
the delivery tank to 500 mm (20 in.) H2O above atmospheric pressure.

6.2 Regulator. Low pressure regulator for controlling pressurization of the delivery tank.

6.3 Vacuum Source. Vacuum pump capable of evacuating the delivery tank to 250 mm (10 in.)
H2O below atmospheric pressure.

6.4 Pressure-Vacuum Supply Hose.

6.5 Manometer. Liquid manometer, or equivalent instrument, capable of measuring up to 500

6.6 Pressure-Vacuum Relief Valves. The test apparatus shall be equipped with an inline
pressure-vacuum relief valve set to activate at 675 mm (26.6 in.) H2O above atmospheric
pressure or 250 mm (10 in.) H2O below atmospheric pressure, with a capacity equal to the
pressurizing or evacuating pumps.

6.7 Test Cap for Vapor Recovery Hose. This cap shall have a tap for manometer connection and
a fitting with shut-off valve for connection to the pressure-vacuum supply hose.

6.8 Caps for Liquid Delivery Hoses.

7.0 Reagents and Standards[Reserved]

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8.0 Sample Collection, Preservation, Storage, and Transport

8.1 Pretest Preparations.

8.1.1 Summary. Testing problems may occur due to the presence of volatile vapors and/or
temperature fluctuations inside the delivery tank. Under these conditions, it is often difficult to
obtain a stable initial pressure at the beginning of a test, and erroneous test results may occur. To
help prevent this, it is recommended that prior to testing, volatile vapors be removed from the
tank and the temperature inside the tank be allowed to stabilize. Because it is not always possible
to completely attain these pretest conditions, a provision to ensure reproducible results is
included. The difference in results for two consecutive runs must meet the criteria in Sections
8.2.2.5 and 8.2.3.5.

8.1.2 Emptying of Tank. The delivery tank shall be emptied of all liquid.

8.1.3 Purging of Vapor. As much as possible the delivery tank shall be purged of all volatile
vapors by any safe, acceptable method. One method is to carry a load of non-volatile liquid fuel,
such as diesel or heating oil, immediately prior to the test, thus flushing out all the volatile
gasoline vapors. A second method is to remove the volatile vapors by blowing ambient air into
each tank compartment for at least 20 minutes. This second method is usually not as effective
and often causes stabilization problems, requiring a much longer time for stabilization during the
testing.

8.1.4 Temperature Stabilization. As much as possible, the test shall be conducted under
isothermal conditions. The temperature of the delivery tank should be allowed to equilibrate in
the test environment. During the test, the tank should be protected from extreme environmental
and temperature variability, such as direct sunlight.

8.2 Test Procedure.

8.2.1 Preparations.

8.2.1.1 Open and close each dome cover.

8.2.1.2 Connect static electrical ground connections to the tank. Attach the liquid delivery and
vapor return hoses, remove the liquid delivery elbows, and plug the liquid delivery fittings.

Note: The purpose of testing the liquid delivery hoses is to detect tears or holes that would allow
liquid leakage during a delivery. Liquid delivery hoses are not considered to be possible sources
of vapor leakage, and thus, do not have to be attached for a vapor leakage test. Instead, a liquid
delivery hose could be either visually inspected, or filled with water to detect any liquid leakage.

8.2.1.3 Attach the test cap to the end of the vapor recovery hose.

8.2.1.4 Connect the pressure-vacuum supply hose and the pressure-vacuum relief valve to the
shut-off valve. Attach a manometer to the pressure tap.

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8.2.1.5 Connect compartments of the tank internally to each other if possible. If not possible,
each compartment must be tested separately, as if it were an individual delivery tank.

8.2.2 Pressure Test.

8.2.2.1 Connect the pressure source to the pressure-vacuum supply hose.

8.2.2.2 Open the shut-off valve in the vapor recovery hose cap. Apply air pressure slowly,
pressurize the tank to Pi, the initial pressure specified in the regulation.

8.2.2.3 Close the shut-off and allow the pressure in the tank to stabilize, adjusting the pressure if
necessary to maintain pressure of Pi. When the pressure stabilizes, record the time and initial
pressure.

8.2.2.4 At the end of the time period (t) specified in the regulation, record the time and final
pressure.

8.2.2.5 Repeat steps 8.2.2.2 through 8.2.2.4 until the change in pressure for two consecutive runs
agrees within 12.5 mm (0.5 in.) H2O. Calculate the arithmetic average of the two results.

8.2.2.6 Compare the average measured change in pressure to the allowable pressure change, Δp,
specified in the regulation. If the delivery tank does not satisfy the vapor tightness criterion
specified in the regulation, repair the sources of leakage, and repeat the pressure test until the
criterion is met.

8.2.2.7 Disconnect the pressure source from the pressure-vacuum supply hose, and slowly open
the shut-off valve to bring the tank to atmospheric pressure.

8.2.3 Vacuum Test.

8.2.3.1 Connect the vacuum source to the pressure-vacuum supply hose.

8.2.3.2 Open the shut-off valve in the vapor recovery hose cap. Slowly evacuate the tank to Vi,
the initial vacuum specified in the regulation.

8.2.3.3 Close the shut-off valve and allow the pressure in the tank to stabilize, adjusting the
pressure if necessary to maintain a vacuum of Vi. When the pressure stabilizes, record the time
and initial vacuum.

8.2.3.4 At the end of the time period specified in the regulation (t), record the time and final
vacuum.

8.2.3.5 Repeat steps 8.2.3.2 through 8.2.3.4 until the change in vacuum for two consecutive runs
agrees within 12.5 mm (0.5 in.) H2O. Calculate the arithmetic average of the two results.

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8.2.3.6 Compare the average measured change in vacuum to the allowable vacuum change, Δv,
as specified in the regulation. If the delivery tank does not satisfy the vapor tightness criterion
specified in the regulation, repair the sources of leakage, and repeat the vacuum test until the
criterion is met.

8.2.3.7 Disconnect the vacuum source from the pressure-vacuum supply hose, and slowly open
the shut-off valve to bring the tank to atmospheric pressure.

8.2.4 Post-Test Clean-up. Disconnect all test equipment and return the delivery tank to its pretest
condition.

9.0 Quality Control

Section(s) Quality control measure Effect

10.0 Calibration and Standardization[Reserved]

11.0 Analytical Procedures[Reserved]

12.0 Data Analysis and Calculations[Reserved]

13.0 Method Performance

13.1 Precision. The vapor tightness of a gasoline delivery tank under positive or negative
pressure, as measured by this method, is precise within 12.5 mm (0.5 in.) H2O

13.2 Bias. No bias has been identified.

14.0 Pollution Prevention[Reserved]

15.0 Waste Management[Reserved]

16.0 Alternative Procedures

16.1 The pumping of water into the bottom of a delivery tank is an acceptable alternative to the
pressure source described above. Likewise, the draining of water out of the bottom of a delivery
tank may be substituted for the vacuum source. Note that some of the specific step-by-step
procedures in the method must be altered slightly to accommodate these different pressure and
vacuum sources.

16.2 Techniques other than specified above may be used for purging and pressurizing a delivery
tank, if prior approval is obtained from the Administrator. Such approval will be based upon
demonstrated equivalency with the above method.

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17.0 References[Reserved]

18.0 Tables, Diagrams, Flowcharts, and Validation Data[Reserved]