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17-05-2006, 07:48 PM #1
Bearing trouble - rotary compressor
We have two rotary compressors that service blast freezing rooms. The bearings on both compressors both went out at the same time. There were thousands of small metal flakes in the oil separator. We have since rebuilt the compressors (new bearings), had outside services (2 companies) rebuild and have run into the same problem. We are now thinking that liquid ammonia could be in the suction line drawn into the compressor. This would put pressure on the shaft and rotary causing the alignment to change and wearing the bearings prematurely. Is this possible? Has anyone seen this before and what would be the signs to know if liquid was actually being drawn by the compressor? Also, is there any chance that liquid ammonia could make it through the oil separator and into the bearing itself to cause more problems? any help greatly appreciated
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17-05-2006, 08:09 PM #2
Re: Bearing trouble - rotary compressor
Hi Rosetennis
If your compressors have failed there may still be some steel in the system.
Liquid carryover would be the most likely, but it would be possible that condensed liquid in the oil would cause premature bearing failure.
Are the oil heater working in the oil sep
Is the discharge check valve after the sep working.
I am afraid to say rotary vane compressors are nearly a thing of the past, being quite inefficient and not well supported by service companies.
Beter to buy a new screw or piston compressor to replace the rotary.
Kind Regards. AndyIf you can't fix it leave it that no one else will:rolleyes:
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17-05-2006, 08:11 PM #3
Re: Bearing trouble - rotary compressor
i would ask the copressor rebuild company they usually can identify the reason 4 ur problem
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17-05-2006, 08:29 PM #4
Re: Bearing trouble - rotary compressor
Hi rosetennis,
Welcome to the RE forum. What type of facility do you have? Cold storage, production freezing, ???
The bearings on both compressors both went out at the same time.
There were thousands of small metal flakes in the oil separator
I'm assuming these are rotary vane compressors and not screws. Is this right?
We have since rebuilt the compressors (new bearings), had outside services (2 companies) rebuild and have run into the same problem.
My guess is (based on the information provided); you have a periodic flooding problem either caused by insufficient capacity on a low temperature accumulator, or the suction pressure is pulling down too fast causing the accumulator to carryover liquid back to the compressors.
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17-05-2006, 10:37 PM #5
Re: Bearing trouble - rotary compressor
Iceman,
We are a public freezer facility. The compressors are rotary vane. I checked the engine logs and the discharge temp is 150 to 160F for these compressors. This is however the reading after the system has stabilized. Could be that on start up we are seeing much lower discharge temps for a while? We typically run at 12 inch vacuum These compressors would also be turned on and off a few times a week so it could perpetuate itself quickly. Any chance that gas ammonia could be recondensing itself in the oil separator after shut down and then being pulled through the oil pump when the system starts up again causing expansion at the bearing or pump?
Additionally, I checked the blast accumulator and the liquid level is actually not that far away from the suction line (suction line is not at top of accumulator but on the side near the top) and the suction line appears pitched towards the compressors.
Please advise. Appreciate your help very much
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17-05-2006, 10:38 PM #6
Re: Bearing trouble - rotary compressor
Andy,
No oil separator heater on the equipment. I am assured the check valve is functioning correctly
Many thanks
Pete
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18-05-2006, 01:26 AM #7
Re: Bearing trouble - rotary compressor
Hi Pete,
I checked the engine logs and the discharge temp is 150 to 160F for these compressors. This is however the reading after the system has stabilized. Could be that on start up we are seeing much lower discharge temps for a while?
These compressors would also be turned on and off a few times a week so it could perpetuate itself quickly.
Any chance that gas ammonia could be re-condensing itself in the oil separator after shut down and then being pulled through the oil pump when the system starts up again causing expansion at the bearing or pump?
My guess is your saturated intermediate temperature is around 10F (-12.2C). For ammonia to condense in the booster discharge line, the air temperature in the engine room would have to be below the booster discharge line temperature. If the compressors were setting outside on a windy Chicago winter day, then maybe...
It would be more possible for the liquid to be sucked backward from the intercooler back into the compressor if the discharge check valve leaked a little.
Apparently the compressors have failed several times. When did it start? What happened in the engine room before the compressors started to break the first time?
Do you use liquid injection for desuperheating of the booster discharge gas or is the intercooler new?
If the intercooler was recently installed I have seen some new intercoolers where the discharge sparger (the pipe that drops down inside the intercooler below the liquid level) can siphon liquid back to the boosters. At the top of the sparger there should be a small hole for a siphon break. The manufacturers drawing should show this.
Additionally, I checked the blast accumulator and the liquid level is actually not that far away from the suction line (suction line is not at top of accumulator but on the side near the top) and the suction line appears pitched towards the compressors.
I don't like the suction line pitched to the boosters, this helps to promote drainage of liquid.
If the boosters are shut down on a regular basis you could have condensation occurring in the suction line. Remember, the suction line is very cold at 12 inches of vacuum.
When the compressor shuts off, the suction gas pressure can rise a little bit. When the gas pressure increases, the saturation temperature of the gas is also increasing. If the the suction pipe temperature is lower than saturation temperature of the gas, the gas can begin to condense in the suction line.
As you can see, there are a lot of possibilities and questions here.
What was the condition of the barrel in the compressor?
Were the blades broken or cracked?
Does the suction line to the compressor come off of the top of the main suction header or off of the side?
Have you tried to close the oil drain valve on the oil separator? If liquid is draining through the separator it has to flow backwards through this line to return to the compressor.Last edited by US Iceman; 18-05-2006 at 01:28 AM.
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