US EPA Method 27 - Determination Of Vapor Tightness Of Gasoline Delivery Tank Using Pressure Vacuum Test
1.1 Applicability. This method is applicable for the determination of vapor tightness of a gasoline delivery tank which is equipped with vapor collection equipment.
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.
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.
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.
Means a liquid-tight division of a 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.
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.
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.
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.
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.
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.
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 my 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
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 mm (20 in.) H2O gauge pressure with ± 2.5 mm (0.1 in.) H2O precision.
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 shutoff valve for connection to the pressure-vacuum supply hose.
6.8 Caps for Liquid Delivery Hoses.
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 184.108.40.206 and 220.127.116.11.
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.
18.104.22.168 Open and close each dome cover.
22.214.171.124 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.
126.96.36.199 Attach the test cap to the end of the vapor recovery hose.
188.8.131.52 Connect the pressure-vacuum supply hose and the pressure-vacuum relief valve to the shut-off valve. Attach a manometer to the pressure tap.
184.108.40.206 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.
220.127.116.11 Connect the pressure source to the pressure vacuum supply hose.
18.104.22.168 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.
22.214.171.124 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.
126.96.36.199 At the end of the time period (t) specified in the regulation, record the time and final pressure.
188.8.131.52 Repeat steps 184.108.40.206 through 220.127.116.11 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.
18.104.22.168 Compare the average measured change in pressure to the allowable pressure change, • p, 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.
22.214.171.124 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.
126.96.36.199 Connect the vacuum source to the pressure vacuum supply hose.
188.8.131.52 Open the shut-off valve in the vapor recovery hose cap. Slowly evacuate the tank to Vi, the initial vacuum specified in the regulation.
184.108.40.206 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.
220.127.116.11 At the end of the time period specified in the regulation (t), record the time and final vacuum.
18.104.22.168 Repeat steps 22.214.171.124 through 126.96.36.199 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.
188.8.131.52 Compare the average measured change in vacuum to the allowable vacuum change, • v, 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.
184.108.40.206 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.
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.
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.