Pressure relief – not unloading or regulating pressure

Questions & AnswersCategory: GeneralPressure relief – not unloading or regulating pressure
Guest Staff asked 6 months ago

Im an apprentice but im currently working pretty much by myself.

I’ve been trying to repair this compressor.

Basically it runs fine, but when i turn the air taps off when the compressor is running instead of it running on low revs, air just escapes from the check valve on the tank.

Iv tried adjusting the relief valve but that is doing nothing. Any ideas on what the problem could be? Email me back of possible

1 Answers
Cas Staff answered 6 months ago


Sounds like there is no pressure regulation at all, and the pressure builds op so high that the safety relieve valve opens.

You need to check the regulating system.

I have attached an image of a similar system.

There should be some regulating valve, this is the valve where you can set the pressure (RV in the image). This valves creates control air by reducing the compressors output pressure (the green lines).

This control air is used to control the inlet valve (load/unload) en the engine speed.

These usually are simply connected in parallel, so when the inlet valve is closed (or partially closed), the engine revs are lowered as well (you can see the green line split up in the image).

If you check the engine, you will see a lever for speed control (you can try to pull it by hand and you will hear the engine rev up or down). This lever is connected to a pneumatic actuator (piston). And this actuator is in turn controlled by the control air which I talked about before. (see image!)

So, since your machine isn’t revving down, and also isn’t closing it’s inlet valve, the problem is *probably* with the control valve, the valve that creates the control air.

You can open it and clean it and see what that does. You can disconnect the control air tube and check if any control air pressure is present.

Hope this made any sense 🙂