IR UP6 – rotary screw compressor problem

Questions & AnswersIR UP6 – rotary screw compressor problem
Cas Staff asked 4 years ago

Have 2 rotary screw compressors that supply air for operation. One compressor is set at a higher pressure and does most of the running.

I noticed the other day that the secondary compressor is cycling more often than normal. During our shutdown period the main compressor never cycles off. The unit was just slightly overdue for service. Changed the air filters, oil filter and the air/oil separator. Unit still has the same operation. The oil level has been topped off recently.

All troubleshooting guides say that it could be a Air Inlet Valve. Can not find any information on how they work. The compressors are in a fairly warm environment, and they do use a lot of oil/coolant in my opinion. Total Hours on unit is 7744 it is an IR UP6 10 150

Please help me.

2 Answers
Cas Staff answered 4 years ago


While reading your question, first thing that came to mind was the inlet valve. Second thing was that there is some big air leak somewhere or a maybe a new machine installed that used a lot of compressed air.

First you should check the following: close the valve that is installed directly after the compressor. The compressor should immediately built up pressure and go to ‘unload’ and stop after a while.

If that happens, you simply have a too big air-demand from the factory. If the compressor still doesn’t built any pressure, you have a compressor problem.

In that case, it is probably the inlet valve. Let me explain.. rotary screw compressors have two modes of operation: loaded and unloaded.

In unloaded condition, the inlet valve is closed, so no air can be sucked in and compressor. The compressor is running, but is not pumping any air.

In loaded condition, the inlet valve is opened, so the compressor can suck in and compress air.

More information about the inlet valve on this page: Air compressor unloader valve / inlet valve

The compressor will normally start up unloaded and go to loaded after a while. When the set pressure is reached, it will go to unloaded. When again the lower pressure limit is reached, it will go to loaded condition again.

So probably, your air inlet valve stays closed. The inlet valve is opened and closed by compressed air which. A solenoid valves controls this. First check the solenoid valve. Also check if there is control air pressure going to the inlet valve (the line might be blocked).

Good luck and let me know if you need more information.

Anna answered 3 months ago

We just had the unloader valve rebuilt on our IR UP6 30hsp rotary screw. When we turned it back on & when it started to load the belt started squealing & we had to shut down. What could cause this?  The tech said this had never happened before. the airend has 57000 hrs on it & he thought maybe it was too weak to run the new valve. What else could be the problem? This compressor is about 10 yrs old but only has 3600 running hrs and 1400 loaded hrs. The airend  went out last year and a used 57000 hr airend is in it until the other can be rebuilt.

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