Hi,

Your question isn't very clear, but I assume your problem is that oil comes back out of the inlet filter.

I'm not 100% sure about this machine, but most smaller Atlas Copco VSD compressors don't have an inlet valve at all or it's just a check-valve.

In either case, there should be a mechanism that stops the reverse flow of oil and shut-down. This is either in the inlet valve (like I said with the VSD machines, it's not a real inlet valve but just a check-valve), or there is an oil-stop valve and a check-valve at the element outlet.

In your case, I would check first if there's an inlet valve (check valve) on top of the screw element. If that is the case, check it for good operation.

If that is not the case, check the oil-stop valve and the check valve below the screw element - these are a bit harder to reach and remove because of oil the oil there.

Hope this helps. Please let me know if you find out anything or have more questions.

Thanks,

Cas