Ammonia liquid carry over

[chichi]

Hi All

As i know screw compressors are resistant against liquid carry over,Is it true?

Is there any comparison between reciprocating compressors and screw compressors against liquid pumping

[gregd1401]

If liquid refrigerant is allowed to enter a screw compressor it will pump the liquid straight into the oil separator. This will then prevent the oil pump from supplying oil into the screw compressor. If liquid enters a recip compressor it will wash the oil out of the sump and may also break valves etc. I dont know of any compressor that will handle any substantial quantity of liquid and any refrigeration plant should be designed to prevent this from happening.

[GBRD]

screw comp cannot tolerate liquid at all. screws may cease & comp will break down. receip comp can probably handle liquid if there are leaks around rings, but would break down eventually. liquid is incompressible anyway.

[ref717]

Agree. No matter what type of refrigerant you are using, rotary screw comps. cannot handle incompressible liquid refrigerant instantly. Recip. comps. can handle only small amounts of liquid but it will not last and soon will lead to compressor damage.

[Segei]

I have a different opinion.
Screw compressors can handle some liquid. Some liquid will evaporate inside compressor because of compression heat and a lot of warm oil. The rest of liquid will go to oil separator and later it can lead to oil pressure drop and compressor will trip.
Recip. compressors have only compression heat to fight the liquid. Major problem with recip. that they have discharge valves. These valves can't pass a lot of liquid and compressor can be blown. Screw compressors don't have discharge valves and they can handle more liquid than recip. However, they aren't liquid pumps.

[charlie n]

Sergei has it right.

[ref717]

Yes, it may be true that the screw compressor is less sensitive to slugging in comparison to the reciprocating type, but a slug of liquid refrigerant may vaporize and interrupt the flow of injected oil resulting in scored rotors. This is the cause of the loud "screeching" noise in screws during liquid flooding. Overhauling or worst, replacement of screw comps. is very costly.

On liquid flooded start, recips. have crankcase oil heater ahead of comp. start-up which boils off any liquid present in the crankcase, but long term repeated slugging will also lead to comp. damage.

Anyhow, it should be remembered that no compressor is designd to handle incompressible refrigerant liquid.

[Sukhvinder]

to avoid ammonia liquid use pump system to save compressor & time! no compressor can ressit liquid, in screw it get into oil sperator & in reciprocating (piston) can break valves, piston or more worse can break crank shaft!