Leakage tests are normally performed AFTER the trench has been partially backfilled. Each valved section of the main is slowly filled with water. Trapped air is released through hydrants and other connections located at high points along the pipe. All the air must be removed before the main is pressurized for testing.
Usually the pipe is pressurized to 1.5 times the expected operating pressure of the system or to the pipe pressure rating, whichever is larger. Class 150 (150 psi) is the standard pressure rating for pipes used in distribution systems and therefore pipes are usually tested to 150 psi. Test periods may vary from two to four hours or longer depending on the level of service the pipe is intended for. Any pressure loss experienced during the test period indicates some form of leak.
The amount of leakage is measured by the volume of water needed to repressurize the pipe back to the test pressure. Water is pumped into the pipe to maintain a constant test pressure. The frequency and volume of water needed to repressurize the system depends on the leakage. Leaks can be detected by examining the trench surface directly above the pipe or by using detectors.
Certain amounts of leakage are allowed on gasketed pipe systems. As per AWWA Standards, the allowable leakage rates for different pipes are given in the following table.
