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Does the height of the water column on top of this pump matter?

  1. Jun 19, 2016 #1
    We are using the following pump to measure the strain on a special tube.

    This special tube is connected on each side to another tube that is connected to one of the two connectors on the pump. (The two connectors of the pump were put parallel to the floor, not like the picture where they are perpendicular.)

    One of the tubes that connects the special tube to the pump has a tube attached to it with a column of water in it. We fill the column of water and we are able to put water through the whole system.

    We reached a problem in our project: we need to redo the experiment in another setting across the city. So we will have to move the whole apparatus and redo our measurements.

    Now, inevitably, the column of water won't be at its same place (it's just a flexible plastic tube that you hang on the ceiling and connects to the other special-tube-pump-connector tube). The column is hung on the ceiling and depending the tables we have there and where we can hang the tube on the ceiling, the column could be bent with an "s" shape or be more horizontal.

    Because we want the strain to be the same between the first set of data and the second set of data obtained, does the orientation of the water column matter? I feel we are doomed... But I am no expert in fluid mechanics. Please help.
  2. jcsd
  3. Jun 19, 2016 #2


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    I think you've got it right. "Head" is the vertical distance from the measurement point to, in your case, the free surface of the liquid.
    If you MUST have the same head, put the assembly on the floor, move to a room with a higher ceiling, move outdoors and string it up in a tree!

    As a technical alternative, you could simulate your water column by terminating the tube in a pressure vessel with the appropriate pressure maintained by other means; or a pre-pressurized vessel large enough so the that volume difference from the pump flow is irrelevant.
  4. Jun 20, 2016 #3


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    Angling or S shaping the flexible tube will make no difference as long as the height of the water level is maintained at the same height above the horizontal measuring tubes. Your best practical approach would be to determine the minimum head clearance at all of your planned test locations and use the acceptable water height for the lowest head clearance location for all of your tests.
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