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B Maintaining a constant volume of water in a tank

  1. May 20, 2016 #1
    I have water draining from a tank A into a tank B through a hole (or short pipe) and then being pumped back from B to A. If I know the rate of the pump (say 19 liters per minute), what should the diameter of the hole be so that the volume of tank A remains the same? The actual volume of A is arbitrary, so I've started with the assumption that I'll use whatever height gives me a velocity of 1.
  2. jcsd
  3. May 20, 2016 #2


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    Staff: Mentor

    Welcome to the PF.

    Weird problem. Can you give us some context? I'd just close off the valves in the system so the levels stay the same.
  4. May 20, 2016 #3
    Doesn't it depend on the height of the water above the hole? I'm not sure what you mean by the height that gives a velocity of 1 ...
  5. May 21, 2016 #4
    I'm constructing a fountain of sorts. The idea is that water flows from Tank A to Tank B, then through a filter and then is pumped back to Tank A. Tank A has an open top, and Tank B has a variable amount of water in it, so I can't seal off the system and pull a vacuum.
  6. May 21, 2016 #5
    The equations I started with used the velocity of the water, which is dependent on the volume (height, depth...) of the water, but that's what I'm attempting to maintain as a constant...
  7. May 21, 2016 #6
    float valve?
  8. May 21, 2016 #7
    The easy answer for home construction purposes is an open trough at the top of tank A, that can handle any flow amount into tank B (it simply pours by overflow into B). Or put the pump on an outlet from tank A directly. It sounds like tank B is an extraneous reservoir for filtering purposes. If so then pump from the bottom of A, thru a filter, and back into the top of A.

    The flow rate depends on the pressure. You can google and find pipe diameter calculators, but the pressure matters. It matters to the pump also. As the filter gets occluded, the pump will pump at lower flow rates from the back pressure building.

    An overflow pipe (like in the back of a toilet tank) will allow tank A to fill, and then handle the variable flow into it with a variable flow out. I don't like the possibility of running tank B dry though, if evaporation happens. Your pump will burn up. Tank B could have a float valve on a water supply, to keep it safe.
  9. May 21, 2016 #8


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    This problem should not be too difficult to analyse .

    We need to be clear about the actual arrangement of the tanks , pipe and pump though . Can you post a diagram ?
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