Where did my oil go?

[craig1]

I have a customer with a copeland 3RA compressor for a fresh seafood case that busted a rod and locked up around 4 months ago. I got the compressor started and it ran for another week on one piston while I ordered parts. I put new rods, pistons, and a valve plate in it and new oil filled to 3/4 on the sight glass.

I don't know what oil level the pump was running at pre-rebuild as the sight glass was too dirty.

I assumed the low velocity of the compressor running on one piston would result in an oil logged evap and that the rebuilt compressor would be overfilled once the oil came back and I would need to drain some. However, just the opposite happened. The oil level dropped to 1/4 in the sight glass and stayed there.


what could be an explanation for this?

[Phase Loss]

My guess would be.......

Before the compressor locked up, the oil/compression rings slightly wore out the pistons cylinder wall. Now that you have rebuilt the damaged piston/rod. You have a slightly larger clearance between the cylinder wall and the oil/compression rings. This is making your compressor pump oil out at a faster rate than before. possibly faster than the oil is naturally returning. You just may have a "pumper" on yer hands now.

[craig1]

"The pumping more oil" scenario is the only thing I could think off also. However, I know the cylinder wall are not worn (no lip at top and bottom of stroke). and the new pistons have rings so they should seal better (old ones did not)

Today I thought of another possibility. The old rods did not have oil passages in them. The only oiling the wrist pins got was whatever splashed up there. The new rods have oil passages to provide pressurized lubrication to the wrist pins. This means more oil gets on the cylinder walls and eventually past the pistons and into the system.


I'm gonna top up the oil and see what happens from there.

[Dowadudda]

if it's running good. leave it alone. 1/4 is fine.

[crackertech]

if it's running good. leave it alone. 1/4 is fine.

Ditto. That's the benchmark for the markets we service 1/4 sg

[craig1]

Thats good to hear that 1/4 is fine. I wasn't sure because all the other comps (3 of which are identical to this one) seem to be between 1/2 and 3/4. This comp has an oil slinger on the motor end rather than an oil pump, so theres no oil safety control. I wanted to be sure it was getting proper lubrication.

[r404a]

have you checked the crankcase for over presure?


r404a

[Super Tech JJ]

Another thing to consider is, how low is the superheat? Copeland wants 20 at the compressor. That will also ensure that your refrigerant is not so dense that is carrying away too much oil.....

JJ