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.
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.
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.
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