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  1. #1
    Join Date
    Oct 2008
    Location
    Panama City
    Posts
    15

    oil separator addition

    Dear people:

    Recently I got a maintenance contract with a medium sized supermarket that operates mostly on medium and low temperature cases paired with small remote condensing units. In some cases the piping is quite long: 90 feet and even longer. According to the log, there had been some compressor replacements mostly related to insufficient oil return. Suction lines seem to be correctly inclined and the risers have traps. I would like to install a couple of oil separators, but Im not very familiar with these devices. From the illustrations, I can see that the oil outlet of the separator is to be routed to the crankcase. Since most of the compressors are of the hermetic type, should I just route the oil outlet pipe back to the suction line? Additionally, I suppose that the oil pressure out of the separator must be quite high (discharge pressure maybe?) therefore, how am I suppose to reduce this pressure before the oil reaches the low side ?. I appreciate any comments.

  2. #2
    Join Date
    Sep 2005
    Location
    florida
    Posts
    5,504
    Quote Originally Posted by friocold2008 View Post
    Dear people:

    Recently I got a maintenance contract with a medium sized supermarket that operates mostly on medium and low temperature cases paired with small remote condensing units. In some cases the piping is quite long: 90 feet and even longer. According to the log, there had been some compressor replacements mostly related to insufficient oil return. Suction lines seem to be correctly inclined and the risers have traps. I would like to install a couple of oil separators, but Im not very familiar with these devices. From the illustrations, I can see that the oil outlet of the separator is to be routed to the crankcase. Since most of the compressors are of the hermetic type, should I just route the oil outlet pipe back to the suction line? Additionally, I suppose that the oil pressure out of the separator must be quite high (discharge pressure maybe?) therefore, how am I suppose to reduce this pressure before the oil reaches the low side ?. I appreciate any comments.
    So what makes you thing a oil separator is going to help?
    I love the smell of phosgene first thing in the morning:

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  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,325
    crackertech has posed a valid question.

    Oil separators do not eliminate the amount of oil in circulation, they only reduce it....ie, there will always be some oil in circulation.

    You state there is adequate suction line pitch (inclination) and they have traps, but are the lines properly sized for good oil return?

    I would check that next.

    Here's a good slide presentation from Temprite explaining oil separators in general:

    http://www.temprite.com/downloads/te...iles/frame.htm

  4. #4
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Quote Originally Posted by crackertech View Post
    So what makes you thing a oil separator is going to help?
    yeagh, so what makes you think that?

  5. #5
    Join Date
    Sep 2005
    Location
    florida
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    5,504
    Quote Originally Posted by Dowadudda View Post
    yeagh, so what makes you think that?
    Uh.....I donoo.Sounds like theirs not enough oil return to separate. among other things.
    I love the smell of phosgene first thing in the morning:

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  6. #6
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    your not catching my humor. I was trying to say "yeagh" like:

    after one kid might say "hey get off my bike" and his buddy says, "yeagh get off his bike"

  7. #7
    Join Date
    Sep 2005
    Location
    florida
    Posts
    5,504
    Quote Originally Posted by Dowadudda View Post
    your not catching my humor. I was trying to say "yeagh" like:

    after one kid might say "hey get off my bike" and his buddy says, "yeagh get off his bike"
    I got ya I"m tired and slow. The rest was info for those that don't get it.
    I love the smell of phosgene first thing in the morning:

    To apply for professional membership click here


    Educational forums are open.

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  8. #8
    Join Date
    Oct 2008
    Location
    Panama City
    Posts
    15
    Thank you very much for your interest.

    Following your suggestion, I just checked the existing suction line sizes for proper oil velocity, and seem to be in the safe range, both the horizontal lines as well as the risers.
    I really do not know for sure if the addition of oil separators would do any noticeable good, but Im pretty sure it is not going to make things worse. From technical literature Ive found in the web I learned that oil separators tend to imrpove heat transfer in both the evaporator and condenser. Besides, since the refrigerant oil only performs its lubricating job in the compressor, why should it be fooling around the system if most of it can be readily returned by the separator? Also, Ive seen similar condensing units (Bohn) which include oil separators as a factory supplied deviced. All of these facts make me believe that the addition of an oil separator should bring more good than anything else.

  9. #9
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    who's paying for it?

  10. #10
    Join Date
    Oct 2008
    Location
    Panama City
    Posts
    15
    The owner of the supermarket is willing to pay for it, as long as I can assure him that the addition of these devices would do no harm to the existing systems but rather would benefit the operation of the compressors. Since I havent been able to find any apparent reason for the repetitive oil-related failures of the compressors, I thought that the use of oil separators was a probable cure.

  11. #11
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,066
    An oil separator would remove a good amount of oil from the discharge gas before it goes through the rest of the system. But there also has to be a reason why the oil that is in the system is not returning. And if that is the problem, a separator would only be a band-aid to the real problem.

  12. #12
    Join Date
    Feb 2007
    Posts
    81
    Is the compressor over sized? If the lines are sized right and sloped properly It sounds like the compressor is too large = lower suction = low velosity = no oil return.

  13. #13
    Join Date
    Feb 2007
    Location
    Northern NJ
    Posts
    646
    when you have these oil failures, what is the oil level in the glass when arriving for service? if it is low, you may have an oil return problem. could be caused by infrequent defrosts, low load, frosting coils, or improper piping, among other things. if the oil level is normal on arrival, you need to check the strainer and contactor (look for delay in coil energizing). also, a high pressure control which is auto reset can cause an oil failure and improper oil return by frequent short cycling. a starved evaporator will cause poor oil return as well. as crackertech stated, you need to return oil in order to separate it.

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