View Full Version : Oil loss when unit is down

01-10-2012, 10:11 PM
I have an ammonia chiller using a compound mycom. When the unit goes down we have an oil loss issue. We have replaced the suction check valve and had a mechanic adjust the flow of oil through the vivkers valve. Now when the operators go to startup they have to turn on the oil pump to unload the 2nd stage. Doing this pumps the oil from the separator into the compressor, suction and inter stage piping. The only way we can get the oil back is to create a pressure differance by depressuring the oil separator and most of the oil returns but not all. This is becoming quite a problem and I am out of ideas.

02-10-2012, 03:34 AM
Would seem the load/unload relay is allowing second stage to load in idle position, passing oil to load cylinder. The load relay is faulty replace it. To check, isolate the oil feed to load unload relay in off cycle.

02-10-2012, 08:50 AM
Sounds like you need to call your Fridge Mechanic, Try turning the rotors over by hand for a few minutes you should see all the oil come back before attempting a restart. !

02-10-2012, 02:42 PM
Turning the crew over by hand does return oil but should not have to be done every time you shut down. This problem all started after a refrige mechanic was on site. I would do it myself but i look after this plant from another country and cannot make it there every time they go down. who is a reliable refrigeration company in Utah?

02-10-2012, 02:44 PM
I have iscolated the vivkers valve ond have been able to rule that out. There is a line from the compressor to the oil separator that has a solenoid valve on it that is closed on run condition and open on shut down of compressor. It is a Henry valve that the operators hear clicking when it should but that doesnt mean the valve is moving. th

02-10-2012, 02:45 PM
Could an increase in oil pressure affect the system like that?

02-10-2012, 11:48 PM
The line between separator and compressor sounds like oil return line from coalesor section of separator, then s/v should be open when compressor is operational. If oil pressure differential is higher than spec'd then compressor could be over injected with oil, possibly increasing amount in coalesor section of separator.

03-10-2012, 10:57 AM
Ferus, where on the compressor this line between compressor and oil separator with solenoid valve is connected? It might be for fast equalisation of suction & discharge line so that reverse rotation is avoided / minimized. There may be a non return valve in the line which keeps a fixed differential in suction & discharge pressure.

The solenoid valve which feed oil to the capacity control cyliner may be passing and therefore the high stage compressor must be getting loaded automatically during plant shutdown.

04-10-2012, 06:28 PM
Sandybapat, it is an equalization line that we did find the Parker valve not operating correctly. i have ordered a new one and will see. I got more infromation from the plant operators,which wasnt easy to get the truth but i found out they had changed out the oil pump a while ago and are running the oil 10 psi higher than before and have pinched off the oil supply to the vickers valve to slow down the speed the compressor unloads. They used to run the oil pump for about an minute to unload the compressor and now they have to run it for 5 minutes which is draining the oil separator and logging the compressor with oil. I had them back down the oil pressure ond open up the regulating valve to the vickers, seemed to work.