Air Compressor Is Leaking Air

There are a number of reasons why an air compressor is leaking air.

In one scenario a fitting is loose on the air manifold of the air compressor. The air manifold leads from the tank to the coupler into which you plug the air line connector, and usually contains the pressure regulator. This line may also be part of the pressure switch mounting or have a pressure relief valve installed in it as well.

If you are not sure exactly where the air is leaking from, you may have to remove any plastic shrouding on the air compressor to have a look. Use a 10-to-1 (10 parts water 1 part liquid dish soap) brushed onto fittings and connections to help find  leaking compressed air. If air is leaking from a fitting, the water/soap mix will quickly show it, as bubbles will form instantly. Tighten fittings as needed, and the leak is gone.

 Unloader Valve Is Leaking Air

When the air compressor reaches the normal cut out pressure and stops, but you notice, while the air compressor is off, that air is leaking out of a valve attached to, or perhaps inside of, the air compressor pressure switch. The valve on the outside of the pressure switch may look something like the one in the image.

Fix My Compressor - Pressure switch unloader valveWhen the air compressor has reached cut out and stopped, the pin on the top of the unloader valve is either depressed or released by an arm from the pressure switch opening the valve to atmosphere, and allowing any air trapped over the compressor piston to escape.

However, if your tank check valve is not sealing properly, then that may be the source of the compressor leak.

The tank check valve, an image of one which is shown below, is typically located where the air line from the pump head enters the compressor air tank.

Fix My Compressor - air compressor tank check valveIf it is no longer keeping the air in the tank due to it leaking, then the tank full of compressed air  flows out of the unloader valve too, until the tank pressure drops to the cut in pressure setting, and the compressor starts again to fill up the tank once more.

If you feel any air leak around or beside the pressure switch it’s a pretty good bet that your tank check valve is leaking. Unplug the compressor, drain all the air from the tank, remove and clean or replace the tank check valve. Air should only flow in one direction through it, so if you don’t mind putting it up to your mouth, try to blow through it in both directions. If air flows both ways, a new check valve would be a good investment in compressor repair.

 Air Blowing Out Of Regulator

Most air compressors will have an air regulator installed on line from the tank to the discharge coupler. Inside the regulator, the part that the air acts on to oppose the regulator spring is a flexible diaphragm. Over time that diaphragm may crack and if that happens then your air compressor will be leaking through the relief hole in the body of the regulator.

If that happens it’s pretty hard to find parts for mini-regulators which are fairly low cost to begin with, so your only option may be to replace the regulator rather than fixing it by replacing the diaphragm.

Any more leaks in your air compressor we haven’t covered? Post a question about leaking air compressors below and we, and other visitors, will try to answer it for you. Only questions and answers about leaking air compressors will be found on this page.


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2 years ago

drain valve won’t close — feels like it may be stripped

Mr glenn
4 years ago

I have a coleman 80 gal upright compressor. modelCV6548049. My leak is coming out of pressure switch, There is a small fitting on the side with the pressure relief valve screwed into it. this small fitting is screwed onto the pressure switch enclosure with a small screw. on the bottom side of this device there is a small hole. it is leaking here. there is a tube screwed onto thew top of it. it is a constant leak. i can put my finger on it and change it a little. It causes the compressor to cycle too often. i don’t… Read more »

4 years ago


My air compressor unloader valve leaking while compressor is pumping what are the problem please someone explain me?

steele honda
4 years ago

Thanks for pointing out that if your tank check valve is not sealing properly, then that may be the source of the compressor leak.

6 years ago

I have a leak through one of the bolts in the manifold(belt drive peerless compressor) it leaks air as the tank fills but stops leaking once the tank is full.I can’t see any hairline cracks.Would i on the right track thinking that a gasket is damaged or a reed not in the correct position?im still using it and I realise that I’m working the motor a little harder but I work fifo and won’t have time to replace gaskets until I’m back if this is the problem.i need a professional opinion please.

8 years ago

I own a harbor freight 8 gal 2 hp air compressor. recently when turned on the tank wont pressurize and I’ve noticed that air is escaping through the exhaust tubing. is this normal and if not what can be the problem of the tank not coming to pressure. thanks so much for any help

david moore