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  1. #1
    Join Date
    Jun 2011
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    375

    Centrifugal Compressors and compression ratio question

    Can anyone explain WHY pumping capacity of a centrifugal compressor decreases so rapidly with relatively small increases in compression ratio?

    Thanks!

  2. #2
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    Centrifugal pumps (refrigerant or water) are not positive displacement pumps. Essentially, they add energy to the fluid. If the energy in the leaving pipe (or condenser) is equal to or just barely less than the energy in the impeller the energy is going to flow backwards or at least not very forward. Also, unlike positive displacement pumps, centrifugal pumps don't have cylinder rings so there is a little more bypass to them. As the differential pressure increases across the impeller, the amount of bypass goes up as well...double whammy!
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  3. #3
    Join Date
    Jun 2011
    Posts
    375
    Quote Originally Posted by jayguy View Post
    Centrifugal pumps (refrigerant or water) are not positive displacement pumps. Essentially, they add energy to the fluid. If the energy in the leaving pipe (or condenser) is equal to or just barely less than the energy in the impeller the energy is going to flow backwards or at least not very forward. Also, unlike positive displacement pumps, centrifugal pumps don't have cylinder rings so there is a little more bypass to them. As the differential pressure increases across the impeller, the amount of bypass goes up as well...double whammy!
    Perfect, thanks I figured it had something to do with the lack of valves.

  4. #4
    Join Date
    Sep 2012
    Location
    Miami, Fl.
    Posts
    9
    Jay guy nailed it, keep in mind it applies to ALL centrifugal equip, pumps, fans, etc.

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