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Need Formula

  1. Aug 5, 2004 #1
    Need to know the formula that i can use it to choose Water Pump ... or suitable ((( Water Pump ))) For any water pip line

    if i have known water tank capacity

    if i have two water reservoirs and need both to not to reach empty conditions
  2. jcsd
  3. Aug 10, 2004 #2


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    Staff Emeritus
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    Can you describe the system a bit more? Pumping from where to where? How fast? How much water? How far (horiz & vertical)?

    Perhaps the Bournoulli Equation? Figure out how much of a pressure head you need and then check pump ratings that can handle that.
  4. Aug 10, 2004 #3


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    Staff: Mentor

    ...and generally, using the info Phobos mentioned, you'd pick a pump straight from a performance graph. The only math is in calculating the head.
  5. Aug 11, 2004 #4
    Is this an open system? Are both tanks at the same elevation? Where is the pump in relation to the tanks?

    The elevation of the tanks and their location relative to the pump is important in an open system, which is a system open to the atmosphere.

    If the system is open, you need to calculate:

    The suction head (height of the water in the tank relative to the pump inlet, the suction pipe friction losses including the pipe fittings and valves

    The discharge head (height to the discharge opening in the discharge tank relative to the pump outlet, the discharge pipe friction losses including the pipe fittings and valves).

    Then you subtract positive suction head from the discharge head or add any negative suction head to the discharge head and the difference becomes the total pump head required.

    If the system is closed (circulating) than changes in elevation do not matter and all you are calculating is the head loss in the piping.

    Also, if the system is open, you have to be careful not to exceed the NPSH (Net Positive Suction Head) that the pump can handle otherwise you can cause the pump to cavitate (create flash steam in the pump that can damage the impeller). This is particularly important if you are dealing with hot water. If the pump is located below the suction side water level this should not be a problem.
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