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The following is a brief outline of the tests that will be conducted during
both the Preliminary and Witness tests:
 | Pressure Decay Test
The integrity of the vapor recovery system must be proven to ensure it's
proper operation. A system which will not hold pressure may permit the
release of liquids or vapors. Leaks may permit excessive emissions and
decrease the efficiency of the vapor collection or processing system. The
pressure decay test is a low pressure testing method which is performed with
all components connected to the piping of new or existing underground
systems or above ground tank systems. For each, the acceptable pressure
decay is dependent on ullage (empty space) in the tank. The smaller the
ullage the more efficiently the test will be performed.
| Dynamic Back Pressure Test (Wet Block)
The vapor return path from the dispenser to the tanks must be sufficiently
large and free of obstructions to ensure the efficient flow of vapors. Traps
in hoses or piping may hold accumulations of liquid which reduce the
effective vapor path and restrict the flow of vapors to the tank. Undersized
piping or obstructions in the vapor-return piping may result in unacceptably
high back pressure. The back pressure test simulates the system operation
and measures the restriction to flow of vapors from the dispensing nozzles
to the storage tank during normal vehicle fueling.
| Air to Liquid (A/L) Volume Ratio Test (vacuum assist systems only)
The air to liquid (A/L) test is designed to measure the efficiency of
vacuum-assisted vapor recovery systems by comparing the volume of vapor
(air) captured and returned to the storage tank to the volume of fuel
dispensed. The A/L test is conducted after the system has passed a pressure
decay test, by simultaneously measuring the volume of air collected by the
nozzle and the volume of gasoline dispensed. Air entering the vapor return
path is measured instead of actual vapors from the automobile tank because
of the difficulty in accurately controlling and measuring gasoline vapors
from the wide variety of automobile fill pipe configurations. |
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