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Thread: oil failure

  1. #1
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    oil failure

    I read in an old post that if a compressor is always running unloaded continuesly if could cause an oil failure?? If so can anyone explain.

  2. #2
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    I would think it is very possible with a system running unloaded constantly- running a reduced head pressure, and a reduced mass flow of refrigerant- similar to a compressor which is running with broken suction valves.

  3. #3
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    Quote Originally Posted by jaybee View Post
    I read in an old post that if a compressor is always running unloaded continuesly if could cause an oil failure?? If so can anyone explain.
    There is something you need to understand about what is happening to the oil while running the compressor unloaded.....

    The refrigerant velocities drop on most systems enough to impede proper oil return, so it would stand to reason that most of the failures could be attributed to low oil levels, not necessarily just running the compressor unloaded.

    Another factor to consider is crankcase heat causing the oil to heat up due to less gasses exchanged which can lead to a lower viscosity..

    Both scenarios could ultimately lead to an oil failure....

    Extended unloaded run time can be OK if the design of the system has taken these issues into consideration.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  4. #4
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    Would this also apply on an rack system ?

  5. #5
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    No, unless the oil system on the rack isn't working properly.

  6. #6
    I agree with GT. Its all about the velocity in the pipes. This is the essential part of oil return. Even on rack with oil separation, oil is still moving around the system. IN winter time and other low load situation the mass flow of the rack will decrease (due to lower pressure ratio) along with the velocity and have potential for logging more oil in the system.

    However, that would probably effect all of the compressor and would probably lead more to an oil slug then a oil failure.

    Different compressors unload differently... hot gas vs blocked suction... etc. I am more familiar with blocked suction. A poor design could create a vacuum in the heads and cause oil to migrate around the cylinders and thus pumped out. This could also happen if there is a lot of wear on the cylinder walls. With hot gas I would think higher temperature and oil breakdown would be more of a concern.

  7. #7
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    Quote Originally Posted by jaybee View Post
    I read in an old post that if a compressor is always running unloaded continuesly if could cause an oil failure?? If so can anyone explain.
    do you have a problem w/ oil failures w/ an unloaded comp??? load it and see if oil failures stop!have you checked the usual suspects??what kind of comp?? recip.or screw??
    as far as i know NO is the answere to your question. you have a 30 hp comp. and 1/3 is unloaded you now have a 20hp...and what is the likleyhood of all compressors on the rack not being on...

  8. #8
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    Quote Originally Posted by pherman View Post
    No, unless the oil system on the rack isn't working properly.
    I agree.

    If you are having oil trips, the unloaded is he last thing I'd look at rather than the first.

  9. #9
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    Quote Originally Posted by sprmktrefertech View Post
    do you have a problem w/ oil failures w/ an unloaded comp??? load it and see if oil failures stop!have you checked the usual suspects??what kind of comp?? recip.or screw??
    as far as i know NO is the answere to your question. you have a 30 hp comp. and 1/3 is unloaded you now have a 20hp...and what is the likleyhood of all compressors on the rack not being on...
    What is the likely hood???? Ha, ha, ha,. Sorry, fellows inside joke.All useal suspects have been checked and if faulty corrected. I just said the h*** with and corrected the unloader situations by removeing a double assignment task in comtrol for that compressor and switch the leads and gained about 25 psi to my 20 psi net oil psi.And so far no more failures

  10. #10
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    How did you gain net oil pressure of 25psi?

  11. #11
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    Quote Originally Posted by jaybee View Post
    What is the likely hood???? Ha, ha, ha,. Sorry, fellows inside joke.All useal suspects have been checked and if faulty corrected. I just said the h*** with and corrected the unloader situations by removeing a double assignment task in comtrol for that compressor and switch the leads and gained about 25 psi to my 20 psi net oil psi.And so far no more failures


    Wha?

    In most situations the oil pressure is the oil pressure, unloaded or otherwise.

    Really the only time you will have an oil pressure fluctuation would be on a Carrier 5H type deal where the compressor uses oil pressure to load.....But the pressure will only drop a pound or two with each stage because of the design of the loader pots.

    I would suspect you have something else going on....to gain more than 100% net oil pressure when the machine loads up is not normal.

    What compressor are we talking about? I find myself very intrigued.

    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  12. #12
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    Jaybee-when you say switched the leads i am assuming that you reversed the rotation by switching L1 and L3 right?...might buy you some time but I think if your oil pump is that worn you should look at replacing it.

  13. #13
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    Talking

    Quote Originally Posted by pherman View Post
    Jaybee-when you say switched the leads i am assuming that you reversed the rotation by switching L1 and L3 right?...might buy you some time but I think if your oil pump is that worn you should look at replacing it.
    Yes Thats what i mean by switching the leads. Ive got and oil pump on my truck ready to go when the call comes. Nobody messes with my ot.

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