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  1. #1
    Join Date
    Sep 2010
    Location
    Nashville, TN
    Posts
    32

    Unloaders on low temp envelope

    Hello, has anyone seen documentation or know why unloaders should not be installed on a low temp compressor. Thanks.

  2. #2
    I think due to they are sized to load accurately and up 15% over load..

    They have them on racks for grocery store.. But even then they would just cycle some compressors off when load goes down.. Unloading comp on racks is fairly new

  3. #3
    Join Date
    Sep 2012
    Location
    northern Ohio
    Posts
    136
    pressure unloaders on reciprocating compressors are pretty common the higher the horsepower. used mostly as a sort of "idle" when between stages of a process during production runs. Injection unloaders are used on a lot of the racks now especially with scroll units. A lot of vapor recovery units run 24/7, they idle nost of the time, load-up only when product is introduced to the system or it gets very warm for a long time. Staging of compressors is most common way to control capacity, but hot gas injection on production lines will keep a big evaporator at a consistent temp. without much change for the compressor. Never saw anything negative about unloading low temp. provided you have good oil management. Can't say i've "installed" any just kept the OEM ones working. I would be interested If you find something.

  4. #4
    Join Date
    Sep 2002
    Posts
    13,511
    I'm kind of curious about that myself. Low gas velocity / poor oil return is all I can think of off the top of my head. Did someone tell you not to use unloaders on low temp?

    BTW: how low-temp are we talking about here?

    PHM
    ------




    Quote Originally Posted by Telecaster1 View Post
    Hello, has anyone seen documentation or know why unloaders should not be installed on a low temp compressor. Thanks.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    May 2003
    Location
    Utah
    Posts
    742
    I have worked on many a low temp system with 5H compressors whe unloading is used...no problemo.

  6. #6
    Join Date
    Sep 2010
    Location
    Nashville, TN
    Posts
    32
    Hello y'all, sorry been busy...thanks for the replies

    Talking mainly about supermarket/commercial refrigeration. Was talking to someone who had taken the CMS test and said there was a question relating to this. Found some literature that may support this, if I figured out how to upload.

    I believe the 5H is an open drive??? No motor cooling needed???

    THX
    Attached Images Attached Images

  7. #7
    Join Date
    Nov 2008
    Location
    Altamont, IL
    Posts
    382
    Copeland (Emerson) bulletin AE21-1216 R13 Unloaders for 4,6,and 8 cylinder comps.
    In GOD We Trust

  8. #8
    Join Date
    May 2003
    Location
    Utah
    Posts
    742
    Yes, the 5H is an open drive compressor.

    Not sure what you mean by motor cooling.

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