PDA

View Full Version : Commpressor damage



ICE/RUNNER
30-06-2010, 05:25 PM
We have had 2 Dorin 2GVS compressors fail with in one moth of each other.
System is R404A +3C chill/-20C freezer 50/60 Hz, 380/460v, condenser is above compressor, no oil separator, no condenser far speed control.

The first one was due to liquid flood back both the intake valve plates were broken and the tops and side of the pistons badly scored.
The second one has got me stumped its got 3 faults
1- The first piston closest to the drive pulley has all the symptoms of liquid damage the bore is scored and the intake valve is in 3 pieces.
2- The second cylinder is the problem the inlet valve is broken but there is no damage what so ever to the piston or bore, however there is a 10MM wide by 18MM long by 2MM deep cavity running from the top of the bore down we cleaned the bore of oil to check for any scoring around the cavity but could find none. I am wandering if it is a casting defect and if any one has had a similar fault.
3- The shaft seal is also leaking once stripped down I found the ceramic ring that is in contact with the outer cover was broken in 4 places. Initial thoughts were loss of lubrication however the oil charge is correct, After the head was examined I put the seal failure down to metallic debris contamination from the broken valves.

Any input would be appreciated.

martinw58
30-06-2010, 06:50 PM
have you got non return valves fitted in the discharge line at comp end and have you taken the discharge pipe higher than the conection on the condenser yo make a trap to stop liquid draining from condenser when comp stops

ICE/RUNNER
30-06-2010, 07:03 PM
We don't have nrv fitted there is no room to fit them either, however the discharge pipe does go higher then the condenser connection, we also fitted 1 unit with a sight glass in the discharge line to check if liquid was draining during off cycle, there was no evidence of liquid over a 14 day period.

DEVIL
30-06-2010, 08:12 PM
Is the intake port lower then the distributor , because of badly sized expansion valve/thermostatic bulb not fitted correctly or not working correctly gas/liquid mixture might get back to the compressor and might flood one of the compressor in the stop period, or flood the running compressor.
Or no solenoid valve before the expansion valve and in the off period liquid might return to the compressor
Avoid this by checking the expansion valves and solenoid valves, and if this dose not fix the problem add a Suction line accumulators

ICE/RUNNER
30-06-2010, 08:32 PM
Is the intake port lower then the distributor , because of badly sized expansion valve/thermostatic bulb not fitted correctly or not working correctly gas/liquid mixture might get back to the compressor and might flood one of the compressor in the stop period, or flood the running compressor.
Or no solenoid valve before the expansion valve and in the off period liquid might return to the compressor
Avoid this by checking the expansion valves and solenoid valves, and if this dose not fix the problem add a Suction line accumulators


The expansion valve is sized right when ever we check the unit there are no signs of liquid at the suction port, we have solenoids and liquid line heat exchanger, there is no room to fit a suction accumulator. Between the compressor and evaporator there is 1.6m of a pipe run.

cadwaladr
30-06-2010, 08:49 PM
make room,put a trap on evap outlet,is the evap a lot higher than condensing unit.

DEVIL
30-06-2010, 08:52 PM
How do you check for liquid in the suction ?
To get the compressor flooded and get the problems you have you need some amount of liquid in it and we aren't talcking of grams.
And you didn't specify is the intake lower then the distributor ?
Amount of refrigerant might condensate in the distributor and flow in the not running compressor if the compressor is in the off cycle for a longer period of time

martinw58
30-06-2010, 09:04 PM
is the heat x faulty leaking liquid into suction line do you have cc heaters fitted

ICE/RUNNER
30-06-2010, 09:58 PM
How do you check for liquid in the suction ?
To get the compressor flooded and get the problems you have you need some amount of liquid in it and we aren't talcking of grams.
And you didn't specify is the intake lower then the distributor ?
Amount of refrigerant might condensate in the distributor and flow in the not running compressor if the compressor is in the off cycle for a longer period of time

The evap distributor is 600mm above compressor, off cycle of comp is at most 10 min.
We had no frost or any sign of sweating on suction valve, valve temp sits around 8c.

cadwaladr
01-07-2010, 12:26 AM
how old is this plant,are crankcase heaters fitted,liquid is getting back to compressor to cause the failure,fit as much gear to stop it happening again,they are cheaper than compressors!

DEVIL
01-07-2010, 04:02 PM
with the evap distributor you mean suction distributor that connects the suction of the compressors together ?
How do you manage to have 8c on the suction on evaporating T of -25-30 deg C ?
off cycle of comp is at most 10 min, you mean of any of the 3 comp ?

mikeref
15-07-2010, 01:58 AM
Should be a pumpdown system with a suction accumulator, nothing less. Also check the compressor is working within specified revs. A 1.6m piperun will be unforgiving when( not if) liquid runs through after startup .

frozenatsea
15-07-2010, 11:28 AM
May be overcharge system ??

NoNickName
15-07-2010, 11:41 AM
How do you manage to have 8c on the suction on evaporating T of -25-30 deg C ?



Straight on spot. Nice question. This is the entry point of our investigation.