Atlas copco GA22 screw compressor has the following problem:
Oil consumption is high.. we suspect problem in oil scavenging line and non return valve functioning?
Could you also share some information on how oil scavenging is carried out through oil scavenging pipe and how does nonreturn valve operates in this type of compressor?
There could be several reasons for excessive oil consumption.
1) It could be that the compressor is running at a too high temperature. I have worked as an engineer at sea, so I know it can get quite hot sometimes. If the compressor runs below 100 degrees Celsius (on the display) or the room temperature is below 40 degrees, this should not be a problem.
2) The wrong oil. Did you change oil recently? If you use the wrong oil, or if you mixed two kinds of oil, it could lead to foaming and oil consumption.
3) As you said, it could be the separator element or the scavenging line.
The oil separator should normally be replaced every 8000 running hours. Is the oil separator still ok? If you remove it and it looks dark and soaked with oil, it is bad (you need some experience to judge this).
It could also be the scavenging line. What does it do and how does it work?
Basically, the oil separator removes the oil form the air by making the small droplets stick together to form large drops of oil.
These drops of oil collect at the bottom of the oil separator filter.
The scavenge pipe/line sucks this oil up and sucks it back to the compressor screw element.
It sucks, because it is connected to the compressor screw element, on the side where a vacuum is created, while in the separator there is a 7 bar pressure.
How to know if the scavenging line is ok?
When the compressor is stopped, remove the flexible scavenging line from the separator tank. You should be able to blow through it with your mouth.
Also, on the other side, where the scavenge line is connected, it is connected to the scavenging pipe. you should be able to blow through it with your mouth.
Inside the separator tank there is the scavenging pipe, which goes to the bottom of the oil separator. You could open the tank and look inside if the pipe is still ok.
About your question about the non return valve: Which one do you mean? The one on top of the separator vessel?
This is a non-return valve and minimum pressure valve.
It's purpose is two fold:
1) To prevent compressed from flowing back in the compressor (for example when the compressor is stopped).
2) To maintain a minimum pressure inside the compressor. There is a spring inside this valve, which is quite strong. There is a minimum pressure required to press against the valve to open it.
This mechanism makes sure that there is always a minimum amount of pressure inside the compressor, even when it is running unloaded.
This pressure is needed to keep the oil flowing around, for cooling and for lubrication.
I believe this pressure is around 2.5 - 3 bar.
Now, sometimes, depending on the model, there is another non-return valve installed at the bottom of the screw compressor element. This one is to make sure there is no back-flow of oil when the compressor is stopped.
Alright, hope this was of any help and good luck with your compressor.
If you have any more questions, just let me know.
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