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Pump water from multiple tanks under vacuum by common pump?

  1. Mar 23, 2015 #1

    rollingstein

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    Is it possible to pump out water from three tanks all under a different vacuum level using a common pump and common suction header? Or would this arrangement cause problems? The destination is a single tank at atmospheric pressure.

    See Sketch below.

    I'm trying to intuitively figure how the pressure profile in the piping would look like.

    D9WD7cD.jpg
     
  2. jcsd
  3. Mar 23, 2015 #2

    Bystander

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    Flow rates? Line lengths and sizes?
     
  4. Mar 23, 2015 #3

    rollingstein

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    Tanks are all next to each other. Line length is approx. 100 ft total from any one vacuum tank till the atm tank. Where to keep pump etc. is flexible. All three vacuum tanks are elevated approximately 10 feet above the atmospheric tank.

    Flow rates are low; approx. 500 Litres/hr from each tank. Line size is flexible too but I was thinking 1/2 inch would be generous.

    Basically, three condensate accumulations have to be emptied out & I was wondering if I could do with one pump instead of three separate ones.
     
  5. Mar 23, 2015 #4

    Bystander

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    Check valves on the exit lines? One and two are going to be self-draining, and three is the only one that will require pumping.
     
  6. Mar 23, 2015 #5

    rollingstein

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    Makes sense thanks.

    Out of curiosity what if the vacuum levels were stronger. i.e. none of the tanks were self draining. Would this pumping scheme work then?

    Say assume 300, 200, 100 mmHg?

    I'm always hesitant to count on a gravity head for draining. That's why a pump would give me a margin of safety. But what I worry hear is a higher vacuum tank pulling from another via the interconnections.
     
  7. Mar 23, 2015 #6

    Bystander

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    How bad do things get if you get backflow into your process/condensate lines feeding these tanks?
     
  8. Mar 23, 2015 #7

    rollingstein

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    Not very bad. It won't be a disaster if there's any intermittent cross contamination.

    So long as, on average, in the long run I can stabilize the system without any inter-flows.
     
  9. Nov 17, 2015 #8
    • Poster was warned about hijacking threads
    Hi,

    Let's say I have an air compressor. If I compress exactly one kilogram of air at STP, I mean the total mass of the sealed tank is one kilogram plus the mass of the tank when empty, it will take a fixed amount of energy to do that. Now suppose my compressor is located at 1km up in the atmosphere. I also operate it to compress exactly one kilogram of air into the empty tank. My question is this; does it take exactly the same amount of energy to compress the same mass of air into the tank regardless of altitude or does the energy required to compress exactly one kilogram of air increase at an altitude of say 1km?

    Or more simply put, does it take more energy to compress the same amount of air at altitude and if so, does that extra energy exactly correlate to the gravitational potential energy ?Thanks.
     
    Last edited: Nov 17, 2015
  10. Nov 20, 2015 #9

    CWatters

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    What stops the three source tanks trying to equalise their pressures?
     
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