Atlas Copco rotary screw compresor sometime builds pressure

Questions & AnswersAtlas Copco rotary screw compresor sometime builds pressure
Cas Staff asked 4 years ago

My Atlas Copco compressor sometimes builds pressure and other times does not.

It seems if I turn the on off switch back it opens a valve sometimes and then builds pressure. It is currently not even allowing me to do that?

2 Answers
Cas Staff answered 4 years ago


You are right, there is a valve which makes the compressor run in ‘loaded’ or ‘unloaded’ condition. It is called the ‘inlet valve’ or ‘unloading valve’ and I have created a page with more info about it here:

The inlet valve sits on top of the screw element and opens and closes the air supply to the compressor.

In your case, it seems it won’t open anymore. It could be that the inlet valve itself is stuck is closed position. But most of the time with this type of problem, the problem is with the control system.

The inlet valve is opened and closed by pressure from the separator vessel. You will see 1 flexible hose run from the top of the separator vessel to the inlet valve.

The valve is controlled by a solenoid valve (small magnetic valve that opens and closes small valve). When the solenoid is open, compressed air opens the inlet valve through a piston. When the solenoid is closed, the inlet valve also closes.

The solenoid needs electrical power to open. I believe it’s 24 Volt in Atlas Copco compressors. The voltage comes from the central controller.

So your problem could be in any one of these components.

Check if there is power going to the solenoid valve (24 volt I believe).

If that is the case, check if the solenoid is opening and closing. I have seen a lot of these valves with so much dirt in them that they just stopped working. Sometimes the problem is in the magnetic coil, which can burn trough sometimes.

If all this is ok, check the flexible hose. It could be plugged with dirt.

Next, check the small control/pilot piston//valve on the side of the big inlet valve.

If all fails, the problem ids probably with the inlet valve itself. Be careful when opening the inlet valve yourself. in older models there is a very powerful compressed spring that can jump in your face. I know a guy that lost a few teeth this way. I recommend not opening the big valve unless you know what you are doing.

I have included a diagram of how the inlet valve works.

Al right, good luck. If you have any more questions, don’t hesitate to ask, I’d love to help.

Premjith answered 4 weeks ago

hi brother .  I have aproblem on my atllas compressor . It suddenly stopp annd  ssignal shows motor faulure .while unloading time and sometimes at loading time  it gets stop  

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