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Thread: Pumping against Vacuum

  1. #1
    Associate Engineer
    Join Date
    Oct 2016
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    3

    Pumping against Vacuum

    I have a vacuum vessel that is half full of water and -0.7 bar vacuum maintained above it. I am constantly filling the vessel with cold water and removing it with a centrifugal pump. The tank outlet is on the bottom that runs down about 3 feet to the inlet of the pump. There is a small line (1/2" or so) that connects the top of the vessel to the pump discharge, balancing the pressure across the pump. My question is what pressure should I see at the pump inlet with -0.7 bar vaccum in the tank above and the pump not running? Should I still see 36 inches of water pressure, or does the vacuum have an effect? Also, when the pump is running, should I still see pressure there (maintain NPSH on the pump)?

  2. #2
    Principle Engineer Cragyon's Avatar
    Join Date
    Feb 2013
    Location
    Newark, NJ
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    218
    Is this homework? What is the application?

  3. #3
    Associate Engineer
    Join Date
    Oct 2016
    Posts
    3
    No homework. Steam is drawn into this condenser that is half full of cool water. We constantly add/remove water to maintain temperature. The condenser is kept under vacuum by two liquid ring vacuum pumps. The discharge of the condenser is at the bottom and drops into the inlet of a centrifugal pump that removes it at the rate we put it in (pump is on VFD).

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