Does your compressor run and run but never fill? One cause might be, has the compressor pump gasket failed.
Many smaller air compressors have a single cylinder with a single piston. That cylinder moves up and down or forward and backward inside the pump. As the piston cycles, that process either pulls air into the cylinder or pushes that air from the cylinder into the tank, depending on where the compressor piston is in the cycle.
Typically, over the piston housing is a valve plate. Often this is a simple flat piece of metal with flappers. Flappers will open and others close when the piston moves one way, and the flappers operation will reverse when the piston moves the other way.
The following photo shows the gasket and valve plate from a Bostitch air compressor. Inside your compressor pump the size and shape will differ, yet the function remains similar.
In this type of pump setup, what separates the high pressure side (the side where the air is driven into the compressor tank) from the low pressure side (where air is drawn into the cylinder) is a gasket. In the image above, the right lower gasket provides the separation between high and low pressure in this model of compressor.
Over time the section of gasket that separates high pressure from low can decay. It gets attacked by compressor oil, perhaps abraded a bit by debris in the air stream, and it weakens.
Has The Compressor Pump Gasket Failed?
The symptoms of a gasket failure is that the pump cycles but doesn’t build pressure at all.
Or, the tank pressure rises to, for example, 35 PSI, and then even though the compressor pump keeps running, the pressure in the tank will rise no further.
If that’s what is happening, a common issue is that at (in this case) 35 PSI, the gasket between the low and high pressure section of the valve plate lets go. Air cycles back and forth between the low and high pressure side, and nothing gets driven down into the tank.
The compressor pump gasket failing is not the only reason why a compressor will run and not build pressure. In the smaller, DIY type air compressors, this, and a failure of the valve on the valve plate, are certainly a common cause.
