Oil change problem

[murray75]

Hi,
Where I work we regularly change the oil in compressors during maintenance visits. Here's what we do...
Start machine: Frontseat SSV: Switch off machine when Low Side pressure is 0.1 Bar: Unscrew filler cap or oil return connection: Suck out oil into empty cylinder: Pump new oil in: Put cap/connection back on: Vac out Low Side of compressor: Wind out SSV until it is cracked off backseat position: Restart machine and adjust oil level if required.

The problem is that sometimes you get gas coming back down the oil return line meaning you have to recover all the gas to change the oil. Does this mean the Oil Sep is faulty? Or should I try to tap it gently to get it to shut off? Any thoughts welcome. Cheers, Murray.

[dhilreefer]

hi,
murry can i know what model you service about oil change problem?

[Grizzly]

without saying what equipment you are working on it's difficult to be exact.
But assuming you have a standard oil return system.
If there is no isolation valve on the oil return line.
Then it may be feasible to pump down as you describe.
Is possible drop into a negative pressure. Dependant upon system.
Then isolate the discharge line, allow sufficient time for internal pressures to equalise.
If it has risen to much, you will have to open the discharge line and pump down again.
Then pull a Vacuum and suck your fresh oil back in.
Or if you have a good hand pump just pump down to say 1/2 a bar.
Use the remaining pressure to push the oil out.
As soon as any vapour appears in the oil dump line shut off.
Pump fresh oil in with hand pump.
Only you can decide which method is more relevant?
Incidentally as a personal preference, on larger recips.
I like to open the sump access cover
and do an inspection of the bottom of the crankcase.
For metal deposits and any other foreign particles!
Hope this helps.
Grizzly