One of the tests prescribed by PEI's Recommended Practices for Installation and Testing of Vapor Recovery Systems at Vehicle Fueling Sites, PEI/RP300. The purpose of the pressure decay test is to ensure the tightness of the piping and valves in a Stage II vapor recovery system.
Before the test begins, the vapor return piping is isolated from vents and vapor processing equipment. Nitrogen gas is then introduced into the piping at a prescribed pressure, and allowed to stand under pressure for 5 minutes. Pressure gauges attached to the piping system are used to determine if the nitrogen maintains its pressure throughout the entire test period. If it does, the piping system can be assumed sound. If it does not, the presence of a leak somewhere in the system is indicated.