Kaeser Compressor will not load

Questions & AnswersKaeser Compressor will not load
Cas Staff asked 4 years ago

I have a Kaeser twin screw compressor we use in our countertop shop. It has worked flawlessly till this afternoon when it stopped building air.

It shows it is on load but will not build pressure.

I believe this has happened once before and years ago so I don’t remember what was done to fix the problem.

I do need this up an running as it is used for the CNC and other processes in the shop. Any help would be great.

1 Answers
Cas Staff answered 4 years ago


I understand that a down compressor is a big problem for a shop like yours, so let’s try to get this baby running again in no time 🙂

When you press the ‘load’ button, do you hear ANY change in sound or pressure or noise?

It is most likely the inlet/unloader valve. The inlet/unloader valve is between the air intake filter and the screw elements. it opens and closes the air supply to the compressor element. If it is closed, the compressor is running ‘unloaded’. If it is open, the compressor runs ‘loaded’.

Since you have a twin screw compressor (I assume they work in parallel here, right? Or is it a low-pressure and an high-pressure element?), you must have two inlet valves.

The inlet valves are controlled (opened-closed) by control air. The control air pressure forces the inlet valve open. Usually, it is closed by spring force (big spring inside).

Since both inlet valves stay closed in your case, it looks like there is something wrong with the control air (would be a big coincidence if both fail at the same time).

The control air is in turn controlled by an electrical solenoid valve. Electric power = solenoid valve open. No electric power = solenoid valve closed.

Please check the following:
1) Is the solenoid working? Can you hear a ‘click’ sound when loading and unloading the compressor?

If yes, than the electrical connections and controller are OK.

If no, check with a multimeter if the solenoid is getting power (usually 12 or 24 volt AC or DC).

If no power, look for loose contact on the controller. Measure directly at the controller. No power there? Than there is something wrong internally.

2) If the solenoid is working (*click, click*), check if there is actual control air passing through.

Open/remove the control air pressure line to the inlet valve. Load and unload the compressor. See if compressed control air is getting to the inlet valves.

Be careful when disconnecting control air from inlet valve(s).. there is no ‘control’ anymore, so pressure might rise too high if inlet valve stays open for too long.

If all this is OK, than there might be something wrong with the inlet valves. But since it would be a big coincidence if both valves failed at the same time, I suspect they ate OK.

If this is a compressor with a low-pressure and high-pressure compressor element, and thus only 1 inlet valve… then it could also be the inlet valve itself.

Be careful when opening up inlet valves, some models have very powerful (compressed!) springs inside, that will pop in your face when opened up improperly.

Here is some more info about inlet valves.

Hope this was helpful and good luck. Let me know if you need any more help/info.

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