PDA

View Full Version : Copeland 6RA oil issues







dkemper
06-06-2013, 04:51 PM
I've got a freshly rebuilt Copeland 6RA compressor that appears to be moving way too much oil.

Unit is a low temp R404 freezer unit, condensing unit has almost no vertical separation from the evaporator.

The compressor had originally failed with a broken rod, the rebuild included new valves, valve plates, pistons, rings and rods along with new bearings and oil pump.

I've talked with the rebuilder, he's at a loss as to what's going on with the compressor.

Crankcase pressures remain at suction or below but the unit is not pulling oil back fast enough to keep it from loosing oil pressure and shutting down. Suction and head pressures are normal for the application. To be honest, I'd expected high crankcase pressures but that does not appear to be the case.

Oil return from the helical oil separator is warm so I've good evidence the system is trying to return the oil, but still, the compressor will empty itself of oil faster than it'll return.

Prior to the rod failure, the unit had ran flawlessly for years.

I'd hate to have to hire a crane to come back out just so I can pull the compressor and return it to the rebuilder for analysis and then reinstall with yet another crane hire. Additionally, this time of year, I really can't afford the loss of the BTU's so I'd really like to leave the thing in-place but somehow I think that's not going to happen.

Anyone have any ideas?

Thanks in advance!

GHAZ
06-06-2013, 06:53 PM
Hi it could a several things. Worn bores or piston rings worn
If the main bearings are slightly worn then the oil gets pushed out towards the motor side and sucked out in the bores and discharged out
And last thing it could be the non return valve in the crankcase which is blocked or not openning and letting oil in from suction

dkemper
07-06-2013, 01:04 AM
Many thanks, think those were about the only possibilities I'd thought of.

Won't be a joyful day, but I might have to pull the compressor, flip it over, pull the pan and check the non-return valve.

Best of my knowledge (and from a trusted rebuilder) the bores and crank are good and within spec, the rings and bearings are new .

Cracking open a compressor on the roof of a building is not really my idea of fun, but might be the best place for me to start before calling out a crane and suffering a couple days down time.

If changing out the non-return valve does not do the trick, I'll need to return the compressor to the rebuilder and eat the down time in the height of the summer heat and the summer production schedule (ice cream/italian ice manufacturing) Grrrrrr.

I've only got a pair of the 6RA compressors in the facility, can't quite justify buying a 3rd from an outside source and ending up with a spare but the temptation is there for that path too.

Maybe a crazy option but I do have a 2 stage 6RB that could be reconfigured as a single stage 6RA, hmmmm. I could better stand to loose the BTU's from the 6RB than the 6RA. Still, even that would be a right pain on the roof of the building.

Magoo
07-06-2013, 02:00 AM
Have you checked that the system is not flooding back to compressor, the possible cause of initial failure which would tend to indicate a TXV problem. Check actual suction vapour temps entering compressor versus the saturated suction pressure/temperature. Another possibility is that the oil separator has junk partially blocking the float return internally in separator, junk from original failure

ISEL
24-06-2013, 09:50 PM
Separator float and oil reservoir check valve. Problematic oil return can be for numerous reasons. The majority of which all boil down to bad pressure differentials in the system. Over-sized pipes running at half capacity can cause too low of a pressure differential and can cause flow issues. Crankcase pressures can also play a big part in oil return as well - maybe having the compressor rebuilt fluctuated the pressures the system was used to seeing and "caused" a part "failure" that wouldn't have been noticed before. What type of oil are you using?