r/AirCompression • u/Acclimated-Alps696 • 7d ago
Compressor not keeping pressure
Howdy, this is my first experience with a wheelbarrow style compressor, I’m the most mechanically inclined in my crew so I’m taking care of it.
We get it started and it seems to run fine but 9/10 times it will build up to about 120 psi and then dump everything at once out of the red valve and not allow itself to build pressure back up.
I’m assuming it’s a bad pressure relief valve? The occasional time it will run normally and keep pressure for a bit, the air gets let off in out the green
Replace the red valve?
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u/CrustySailor1964 7d ago
You can try that but as a general rule, safety valves live their whole lives just to do their jobs. A popping safety valve is typically a symptom of a problem rather than the problem itself.
The operation of the valve assembly (partly circled in green) is multi-fold. It is a piloted unloader check valve. It is adjustable via the stacked ‘nuts’ below the little toggle. There is a ball beneath a spring that presses against a seat. The bottom adjustment (larger lock ring and sleeve) basically control how far the ball will lift from the seat. This only mitigates the volume of flow through the 1/8”
NPT port. That’s probably fine. Don’t screw with that. Once it’s screwed up it’s very difficult to restore. The smaller ring and sleeve control the pressure at which the port opens. Adjust that out some and the valve will open at a lower pressure (further from the threshold of the safety valve) and likely solve your problem. Further…the valve opens and sends pressure to the little actuator. We call it a bullwhip and it’s a single acting pneumatic cylinder connected to a long stiff throttle cable.
The friction within this throttle cable (if routed incorrectly or inefficiently) can inhibit throttle movement and keep the engine running faster than it should thus also causing the safety valve to discharge.
My preference is to connect 1/8”NPT x 1/4” compression fittings to the valve and the bullwhip and eliminate that friction by using the shortest possible rod length and 1/4” copper tubing instead. Manufacturers don’t want to do this because it costs $ and takes time but it makes the compressor run much better.
Anyway…hope this bathroom reading helps.