Air compressor safety (pop-off) valve leaking air

Symptoms

• Steady hiss from the small valve on top of the tank
• Leak stops when the valve's ring is pulled and released
• Leak happens even at normal, well-below-max pressure
• Valve leaks worse as pressure rises

Likely causes

• CommonDebris or corrosion on the valve seatSmall particles can prevent the valve from sealing fully.
• CommonWorn valve spring or sealOver time the valve loses its ability to seal until pressure actually requires release.
• PossibleValve stuck slightly open from lack of usePulling the test ring periodically keeps it seating properly.
• Less commonActual over-pressure situationIf the pressure switch fails to cut off the motor at the correct point, the tank could be over-pressurized, which is a genuine hazard.

What to do

1. Check the tank gauge to confirm the pressure switch is cutting the motor off at the correct, normal pressure and not letting it climb higher than it should.
2. With pressure released and the compressor unplugged, pull the safety valve's ring a few times to let it snap open and closed, which can dislodge minor debris.
3. Repressurize slowly and watch whether the leak stops or continues.
4. If it still leaks at normal pressure, do not attempt to disassemble or adjust the valve; these are sealed, non-adjustable safety parts.
5. Replace the safety valve with an exact-match replacement rated for the same pressure as the original.
6. Never plug, tape over, or otherwise block a leaking safety valve to stop the hiss; that removes your tank's over-pressure protection.
7. If the pressure switch itself seems to be letting pressure climb too high, have that inspected immediately, since it's a separate and more serious problem.

Tools and parts

• Adjustable wrench

When to call a pro

If pressure appears to be exceeding the normal cutoff before the safety valve releases, stop using the compressor and have a technician check the pressure switch right away.

Safety