How can I adjust clearances in screw air-end

Questions & AnswersCategory: GeneralHow can I adjust clearances in screw air-end
Saeid asked 1 year ago


I have 2 questions : 

1 – What is main diffrences between air and refrigerant screw compressor? I know sealing in air compressor is not suitable for refrigerant but why large-scale air compressor manufacturers do not prepare their compressor for refrigeration cycles by making small changes (especially in sealing) to their compressors? (Because of the higher price of refrigeration compressors)

2- We have an EVO3 Rotorcomp twin screw air-end and I should change two tapper bearing of it. Now my question is how can I adjust clearances between rotors and between rotors and other parts after changing bearing? 

Best regards

Saeid Khoshnoodi

1 Answers
Cas Staff answered 1 year ago


Great questions – but I believe there are a lot of differences in compressed air screw elements and refrigerant screw elements, although the operating principle is the same.

(I’ve actually worked on a reefer ship for some time where we had two of these units – unfortunately there was no need to overhaul them during my time on the ship).

Look at this video:

Look how big the sealing housing is and the seals that go in – that’s no cheap. Most of these men do seems to be installing the seals. Also at the beginning you can see the completely open screw element – it has an extra open chamber around it – probably for helping keep the refrigerant inside.

Also, as far as I remember, capacity control on refrigerant screws is often by sliding valves in the screw element (to ‘short circuit’ part of the screw) – while this is available on some old models of screw compressors, this is generally speaking never used anymore on compressed air screws (capacity control is by using an inlet valve or variable speed drive).

But – I’m not an expert on this, so if anybody wants to add some info in the answers here, please do! 🙂

For your second questions: you do that with a spacer ring. There should be a spacer ring in there right now, matching the current bearing. If you change bearings, you should re-measure the clearance and adjust the spacer rings (exchange for slightly bigger/smaller one).

Hope this helps 🙂