[Al Skierkiewicz]

Tom,
In addition to Jon's advice, the pressure relief valve may not (more than likely not) be calibrated. It is possible for this device (the big brass hexagonal fitting) to be calibrated at less than 120 psi which would run the compressor all the time while releasing air from the valve. The pressure switch will shut the compressor off somewhere between 115 and 120 psi showing on the high pressure gauge. During inspection we will check this operates as expected as well as checking the calibration of the relief valve.