One Reason An Air Compressor Bleeds Compressed Air

air compressor leaks and bleeds
(Last Updated On: October 5, 2020)


My air compressor is set at 80 psi. It pumps to this setting and as soon as it shuts off you can hear a leak from a valve at the back.

Then the pressure drops quickly which causes the compressor to recharge.    Do you think an o ring has gone?

You can feel the air coming out only when it has stopped pumping. The escaping air is from sort of screw attachment to a valve on the top at the back of the tank. Can you tell me why?   How do I fix?


Our Answer…

It’s hard to be sure without seeing it, but I suspect that “the valve at the back” is the unloader valve for your compressor.

It’s supposed to open when the compressor stops to “unload” the air that’s compressed over the piston.

air compressor leak

So, when your compressor reaches the high pressure cut-out, the unloader valve opens, you hear that characteristic “psssshhhhtttt”, and then the air stops.

Only, in your case, it’s not stopping.

That tells me that the air (again, assuming that it’s the unloader valve that the air is leaking from)is bleeding back out of your tank, up the air line to the unloader valve, and out to atmosphere.

When your compressor is compressing air, it’s pushing that air down into the tank through a one-way valve (also known as a check valve). That valve is supposed to keep the air in the tank when your unloader valve opens.

I think that either your check valve has a worn seat, or there is debris that’s preventing it from closing tightly, and that’s where the air is coming from.

If you are up to it, make sure the tank is empty and the compressor is unplugged, and look for where the air line from the compressor head goes into the tank. There should be a check valve assembly there. Dismantle it, make sure that the internal valve flapper or ball is seating cleanly, reassemble and test.

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


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