Symptoms
- Hissing sound for a few seconds right after the motor stops
- Pressure drops slightly each time the motor cycles off
- Sound seems to come from near where the pump connects to the tank
- Motor cycles on more frequently than it used to
Likely causes
- CommonWorn or stuck-open check valveThis valve should seal to keep tank air from flowing back into the pump when it stops; wear lets it leak.
- PossibleDebris caught in the check valve seatA small particle can prevent the valve from sealing fully even if it's not fully worn out.
- Less commonCheck valve spring weakenedLess common but possible on older units.
What to do
- Listen carefully right as the motor cycles off to confirm the hiss is coming from the check valve area near the pump-to-tank connection, not a different fitting.
- Release pressure and unplug the compressor before removing the check valve.
- The check valve typically unscrews as a single unit from the tank fitting near where the pump discharge tube connects.
- Inspect it for visible debris, wear, or a spring that doesn't snap back firmly.
- Clean it if debris is visible and reinstall to test, though replacement is usually more reliable than cleaning.
- Install a new check valve with thread tape on the threads if the old one is worn.
- Repressurize and listen again after the motor cycles off to confirm the hiss is gone.
Tools and parts
- Adjustable wrench
- Thread seal tape
Compressor check valveSearch: “air compressor check valve replacement”
When to call a pro
This is a straightforward DIY part swap; a pro isn't usually necessary unless access to the valve is difficult on your model.
Safety
Use caution
Fully release tank pressure before removing the check valve.