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Compressors that Do Not Build Pressure

So you notice that your air compressor will not build pressure.
It runs and seems like it’s working just fine. The air pressure in the tank plateaus at certain point, like 40 PSI for instance, and though the unit runs continuously, your compressor just won’t build pressure past that point.
This leads to yet another problem, aside from not being able to get enough air to your pneumatic tool. An air compressor that does not build pressure runs on long past the point where it would usually reach the cut out pressure level and then stop. This means the compressor motor will eventually overheat.
Although the compressor motor might shut down because it has a thermal cut off switch, overheating is never a good for the motor. It also has negative effects on the compressor start and run capacitors. So if your air compressor is not building pressure even though it is running, it’s best to shut it down until you fix it.
Why Your Air Compressor Will Not Build Pressure
Compressor Intake Valve Failing
As the reciprocating air compressor is on the intake cycle, its piston moves away from the intake valve that opens as the piston moves to pull a bit of a vacuum. Then air from outside the pump head goes into the cylinder through the intake filter. The piston moves into the compressor cycle, and the air pressure building up inside the cylinder closes the intake valve.
If the intake valve in your compressor has been compromised, the common symptom to watch out for is air blowing back out of the intake port.
Compressor Pressure Valve Failing
This is a little harder to diagnose. When the compressor piston is moving to the compression stroke, the increasing air pressure in the cylinder closes the intake valve. Almost simultaneously, the pressure valve is also blown open.
The pressure valve lets the compressing air into the air line to run from the pump head into the tank. If your valve is failing, air will flow into the line to tank but when the piston moves into intake cycle, air will flow into the piston from the intake valve but also back up the line from the tank into the piston. This will not allow pressure build in the tank past a specific point.
These two are the most common reasons your compressor will not build pressure. If you are not sure which of the two is causing you problems, or if you believe there may be other underlying causes, it’s important that you call a professional to check your air compressor.

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