Why is it a compressor will not build pressure? Does the following describe what’s happening, or rather, what’s not happening, on your compressor?

The motor runs and runs. The pump sounds like it’s operating, but the air pressure in the tank is not rising in pressure at all. Or, the pressure in the tank rises to a certain pressure level and then the pressure stops rising, even though the compressor continues to run and run.

Here’s why a compressor will not build pressure.

The air compressor is really a pump driven by an electric motor, or perhaps with a motor driven by other fuel types like gasoline or diesel.

The part that actually compressors the air is often referred to as the pump, or compressor pump.

Cylinder And Pistons

This is an air compressor pump, though it’s missing the pump head cover in this photo.

In the photo above, part of what’s missing is the pump head, which will contain an intake port. This pump is also missing the valves or valve plates which open and close depending on whether the pump is in the intake or compression cycle.

On all compressors the pump pulls in free air from the atmosphere through an intake. That intake port on the pump typically has a filter on it to keep dust out of the pump. The pump is then supposed to drive the air it takes in into the tank, and in so doing increases air pressure in the compressor tank.

Different styles of air compressors, reciprocating versus rotary screw for example, accomplish this with different methods, yet they pretty much all do the same thing, suck in air from around the room or through an outside air intake and drive that air into a tank to build up pressure.

When a compressor pump is driven by an properly working motor, and the pump is cycling, why won’t the pressure in the tank build? Next comes things to check.

What to check on an air compressor when the compressor will not build pressure?

The air compressor reed or flapper valves (also known as the intake and pressure valves, or suction & discharge valves) are a common cause of why an air compressor will not build pressure.

The image below shows the valve plates (top of the photo) and reed valves (bottom left of photo) from one smaller air compressor. It also shows the gasket (bottom right in the photo).

Compressor Valve Plate

Compressor Valve Plate Kit

If the compressor valves or gaskets are what the pump problem is, then it will be necessary to disassemble the pump to repair that problem. The issue is in determining whether it is the valves that is the problem.

One clue to a prospective valve problem is if air is exiting the intake port when the compressor is cycling. Removing the intake filter briefly will help determining this. If air is escaping there it’s a pretty good bet that the intake filter flapper is damaged in some manner.

If it’s the pressure side reed valve, or if the pump head gasket that is creating the problem, that’s harder to diagnose, yet the symptoms are the same. Either no pressure builds in the tank or the tank pressure increases to a certain point and then stays there, regardless of how long the compressor runs. That might even result in the compressor shutting itself down if the motor overheats.

The only real check here is to pull the pump head off and examine what’s what. If a reed valve is damaged, that’s usually pretty obvious. If the gasket its weakened and blowing open at a certain pressure, that’s harder to see.

The solution to the latter is to replace the gasket regardless of whether the reeds are damaged or not.

That’s not all. What else to check when an air compressor will not build pressure?

So, start pulling the pump apart, but wait, before you do that, there are other reasons why an air compressor will not build pressure. Pretty much all of them are found here on this liked page.

Get some help with a compressor that will not build pressure!

You can certainly use the form to ask a question about what to do when your compressor will not build pressure.

Please provide as much information about what your compressor as possible. The make, the model, the age of the compressor, how much it is used, the type of power supply… anything that you can think of that will help us (myself and the many visitors) help you with this air compressor problem.

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