Here is a quick tank check valve checkup.
Most DIY and smaller air compressors have a compressor tank check valve. It is typically located where the air line from the pump head enters the compressor tank.
Why bother doing a tank check valve checkup?
Typically it’s because your air compressor does not hold air. The compressor fills the tank, the compressor stops, and over time – maybe a minute, maybe overnight – the compressor tank empties on it’s own.
If you have left your air compressor plugged in, that means when the tank pressure reaches cut in, the compressor will start. That is not something most of us want happening in the middle of the night from an air compressor that’s in the basement that’s right under the bedroom.
In the photo below, the tank check valve is commonly found where the red dot is. That is, where the line from the pump head enters the compressor tank.
If you found that your compressor loses air over time, the first check would be the tank check valve. Does it actually seal?
Find a tank check valve on Amazon here; New In tank Check valve for air compressor 3/8″ comp x 1/2″ mpt
How To Do A Quick Tank Check Valve Checkup
Unplug the air compressor.
Drain all the air from the tank.
Remove the line from the pump where it is attached to the fitting at the tank if it has only one, or both lines if your compressor has a line over to the unloader valve as well.
Put a wrench on the flats of the fitting, and turn (normally counter-clockwise) until the thread seal releases.
Continue turning the fitting – complete with tank check valve – out of the tank.
Wipe it clean.
You will normally see three or four holes on the sides of the check valve near the bottom.
Place your lips over the check valve to seal around the valve – not blocking those holes – and blow… hard!
If air comes out of the hole either where the line from the pump was plumbed, or out of the port for the unloader valve line, you need to clean, rinse, and test your tank check valve again.
If you cannot get the tank check valve to stop air coming up out of the tank after a thorough cleaning, we suspect it will be time to acquire a new one like the check tank valve for air compressors below.
Hi Bill, I Have a unknown brand air compressor where a goose neck line runs from sump top block to bottom pig tank. It’s a inline valve. There is a small 1/8 ln hole on the nut face of the valve. Tank has some pressure but oil shoots out my dip stick until I shut it off air continues to blow out both sides of vent on dip stick, until all air pressure is drained from tank. My hope is the check vale has failed that causing the oil blow back from the dip stick vent as opposed to bad seals where it’s blowing past the piston rings and seals. Any thoughts would be appreciated.
Hi Tommy, It definitely looks like a check valve failure because the air continues to blow until the pressure in tank is drained. If the air was due to bad seals it would have stopped within seconds of the compressor stopping. Try replacing the check valve.