Unlloader valves and throttle on gas compressor engine

by Joseph Marsh
(Poughkeepsie,NY)

We are restoring a Whiting T2MA car mover and have had no luck on getting in touch with the company. It has a single cylinder gas engine driving a 2 stage air compressor. It make air persure just fine and when we turn the gas engine off we can hear the PSSSCHRT which dumps the presure from the cylinder heads through what looks like a valve that is controlled by a line from perhaps an oil pump on the compressor shaft. However we just keep building air presure and at 180 PSI we shut the engine off. Should the same unloader valve also control the presure in the tank unloading the cylinder heads ? There is also what looks like a blow off right next to the compressor controlled unloader valve.

Thanks for your help
Joe

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Bill says...

Joe, gas operated compressors are often "demand" type, meaning that the engine runs all the time, yet the compressor only compresses air (and throttles up the engine) when the pressure in the system drops.

You have a control issue, a combination of pressure switch and engine throttling I expect. Yours is not working right and you definitely should not have to rely on someone to shut off the motor at the high pressure level. This should be automatic in the system.

Cheers,

Bill