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First stage compressor relief valve blowing open and staying open while cycling


Jun 23, 2002
Vancouver BC Canada
Hi All:
I;m having a compressor problem with the interstage overpressure relief valve opening and staying open while the compressor pumps from the first stage to the second stage.
It's slowly getting worse over time and now pisses air right until the compressor shuts off at 150 PSI.

I don't know enough about compressors and how they work to diagnose what the root cause is.

So it's a two stage 5hp 80 gallon Gardner Denver recip; set up to give 120 to 150 PSI.

Are the springs in the overpressure relief valve shot which would mean replacing the valve?
Is the interstage pressure higher than it should be from the stage 1 side and what might cause that?
Is there a valve between stage one and stage two that could be failing and allowing 2nd stage air back into the interstage piping?
Is there something I do not understand about how these compressors work that could account for this?.

Thanks in advance.


replace the pressure relief.
you could always put a T in there and put a pressure guage on a long hose and see if it really is going over pressure.
if so then it might be something in the second stage that could be blocked with crud or dirt.
ususally you can take the top apart with the reed valves. could have the second stage reed valve stuck open pumping air back into the first stage. tubing
take off the second stage output tube and see if that is free flowing to the tank and if the pump is outputting air.
also as there is a check valve to prevent the air flowing backwards from the tank to pump when shut off.
I believe you will find that the intake valve for the second stage is leaking causing the over pressure vale to release the excess pressure. Bill
If it's just a faulty relief valve... Then that is the way it should fail. Never had one fail on me but they don't cost much.
I'm confident that you will find a valve problem on the 2nd stage. Intake or discharge.
It's been a long time since I've worked on a "headless" compressor, but I would expect the valves to be accessible from an external cap.