We are experiencing problems with our rotatory screw air compressor regarding its loading and unloading.
Set point for Loading is 6.2 Bar & Unloading is 7.2 Bar. But when the compressor starts to load its builds up pressure too fast within few seconds and shows the discharge pressure 7.5 Bar and the compressor starts to unload but actually the Air receiver pressure is going to 6.4 Bar only.
It unloads the pressure suddenly drops from 7.5 Bar to 6.4 Bar. Also we have observed the amperes are high during Loading and remains higher than usual during idle running in Unloaded condition.
We recently changed the Oil separator elements and the oil- differential pressure showing 0.3 Bar. We have also changed the receiver Blowdown solenoid vv and Inlet control solenoid VV with new ones but result is same. We also overhauled the Inlet and Discharge VV. We checked the discharge piping till Receiver and it has no obstruction.
We have replaced the Pressure sensor also so and it gives the same result. Your advice on this will be highly helpful…
There must bu a blockage between the air compressor and the air receiver.
This is sounds 100% like a blockage, so please investigate further.
There could be a number of things between the screw element of the air compressor and the air receiver:
- oil separator
- minimum pressure valve
- compressed air dryers
- compressed air filters
You checked number 1 and 0.3 bar pressure drop is OK.
You also checked for blockage between the compressor and the air receiver, so I assume 3, 4 and 5 are OK as well.
Leaves us with number 2: the minimum pressure valve.
This valve sits on top of the separator vessel. It opens when a certain minimum pressure is reached (it’s needed for the correct functioning of the air compressor).
In you case, it may be stuck or don’t open completely.
It’s a pretty simple valve, so you can open it and check for any problems, clean it, etc. Best of course to get an overhaul kit and change all o-rings, gaskets, etc.
Hope this helps,
All the best,