PMC GHO, IPM OP series, Graco T2 Transfer Air motor performance
Rebuilding the entire transfer pump can get expensive and may not be required. After much use, the transfer pump air motor starts operating sluggish and leaks air. This is generally due to deforming (wear) of the upper reversing spring and the upper air valve gasket. The spring shows this wear generally in two ways. The first being the pump fails to return to the down stroke and secondly the pump will pause momentarily when reversing to the down stroke which appears as a cavitation type action. Changing the spring is the best solution, but when in a pinch, stretching the spring to its near original length can get you through the day.