Carlyle 06NA reversing

[frankv1@maltane]

Hi

I have a problem with a Carrier 30HXC Chiller . Each of the two circuits has two Carlyle 06NA compressors. On switching off , one of the compressors reverses rotation due to gas back flow.
( The whining noise of the screws reversing). My first assumption was that the discharge check valve was stuck or damaged. On inspection and testing the discharge valve sealed tight and showed no damage. Tests where carried out with the check valve housing removed from the compressor.
My only idea is that there is not enough back flow of gas to push the plunger on the seating when the compressor switches off.
Any help would be greatly appreciated as this compressor works fine except for this problem.

Thanks​

[chillerman2006]

Screw compressors are designed to run backwards when they stop... Reverse Thrust

its the other three that dont reverse thrust when stopped that need looking at

R's chillerman

[frankv1@maltane]

Thanks for the reply.
We have a chiller farm with 14 30HXC chillers installed and not one compressor reverses in this way when stopped.I would expect a small ammount of reverse until the check valve closes but this compressor goes on for about 10 seconds and that is way too long.