Why Your Pressure Switch Might Be Leaking Air

Technician assembling air compressor pressure switch
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Why Your Pressure Switch Might Be Leaking Air

Why is my pressure switch leaking air?

The pressure relief valve on the side of the on-off pressure switch is designed to release built-up pressure in the air compressor pump head and lines. It does this by turning off when the air compressor reaches the maximum pressure allowed by the pressure switch.

  • When this happens and your air compressor is working properly, you will hear air release from the pressure relief valve for 3 to 5 seconds before it slowly stops.

When the air continues to leak from the pressure relief valve, you will need to look at the one-way check valve that is in your air compressor tank.

  • The Check Valve allows pressure to go from your air compressor pump directly into the air compressor tank in only one direction.
  • When this one-way check valve is operating properly, the air can only go into the tank and is then prevented from coming back out of the air tank by the check valve.

Diagnosing a faulty check valve in 4 steps:

When the check valve is defective, damaged, or worn, the compressed air in the tank can escape and travel back past the one-way check valve. This compressed air will now look for a place to escape and will typically leak out from the pressure relief valve located on your on-off pressure switch.

  1. Locate the check valve at the end of the main outlet line that comes off of the air compressor pump and goes into your air compressor tank. 
  2. Remove this line from the air compressor pump and the air compressor tank.
  3. Test the check valve by removing the small link that is attached to the pressure relief on your on-off pressure switch and verify that the air is escaping from the air compressor tank through the line, meaning you have a bad check valve.
    • If no air is coming from the line and the switch continues to leak, it means you most likely have a bad diaphragm on your on-off switch. 
  4.  After confirming the source of the problem, access and replace your check valve.
Geoff Anderson
I purchased two switches on Amazon and returned them, thinking they were defective because they were leaking air from what appeared to be inside the brand-new switch. After reading your post here, I determined the problem was never with my switch and ordered a new check valve for my Porter Cable air compressor. I installed the new check valve, and now I no longer have a leak. Geoff A