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Pykester1
13-05-2008, 09:06 PM
Any suggestions?
I have two Copeland semi hermetic reciprocating compressors mounted on a frame connected in tandem with one common suction line and one common discharge line connected to one remote condenser and one evaporator (Glycol heat exchanger.) The system also has one common oil balance line and gas balance line. One comp is 10 HP and the other is 15HP. The system has one common oil sep that injects into the oil balance line. I have recently discovered an unusual problem. After having intermittent oil trip problems with each compressor and each time being unable to diagnose the problem because the oil pressure is always ok when I arrive on site, I noticed that while the 10 HP comp is running away nicely, and the 15 HP is sitting idle, (load satisfied,) the 15 HP compressor is sweating over the whole of the body of the compressor. From the tee in the suction line, (2 1/8",) up to the suction rotolock, through the winding part of the body right up to the head, the thing is dripping wet, yet it is not running. It appears as if the suction gas returning to the pack is flowing through the idle compressor to the running compressor via the oil balance line. The oil balance line is also sweating. I have checked that the gas balance line is open and it is. What I don't understand is why the gas would take the route of the idle compressor when it can easily travel straight to the running compressor. There are no blockages. I thought the suction rotolock valve strainer may be blocked, but neither compressors have strainers. I have checked valve plate and head gaskets and all are okay.
Any suggestions?

fowlie
14-05-2008, 12:43 AM
hi pykester1-are you getting sweating on the oil or suction line on the 10hp compressor as well or is it just the 15hp one.what are your oil levels like on the oil floats

wambat
14-05-2008, 01:02 AM
Sounds like the oil float in the seperator is stuck in the open position and discharge gas is flowing in to the low pressure side of the running compresser
via the idle compressor

Pykester1
17-05-2008, 11:17 AM
Hi. Both compressors are sweating as bad as each other. Oil levels are good.

Pykester1
17-05-2008, 11:26 AM
Hello wambat. That sounds like a good theory. I had thought this may be the problem, as I have already replaced one separator a couple of years ago as it kept sticking and tripping the compressors out on oil level failure. There is a lot of dirt in the system and I have had to keep replacing the 305 filter/driers. They are always blocked solid. (At least once a year.)
Thanks for your suggestion. You have confirmed my suspicions. Nice one.
All the best.

hendry
18-05-2008, 05:06 AM
Hi pykester1,

i see it as some form of liquid flood back.

normally, i'll check my design & settings at evaporator & compressor to satisfy my quest.

hope that helps.

hendry, on wesak day holiday.