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Thread: pumping power for filling tank from bottom vs top

  1. #1 pumping power for filling tank from bottom vs top 
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    Which will take more power/energy'
    pumping water for filling tank from bottom/base?
    or from top of tank

    Pump- Centrifugal
    same tank


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  3. #2  
    Forum Cosmic Wizard
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    I am assuming you are setting your pump at the same height in both cases.
    From the top because then you have to lift all the water to the top of the tank and drop it in while if you pump from the bottom you only have to lift the water to the level you are full to.
    Think of the pump as working against pressure and the pressure gradually rises as the tank fills. If the pipe has to go over the top of the tank you are puming against the full head of water pressure the whole time you are filling the tank.


    Last edited by dan hunter; February 15th, 2014 at 10:57 AM. Reason: typo corrected
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  4. #3  
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    suction head is same
    height is 100ft from suction eye
    Tank volume is 500 litres
    line daimeter is 0.5in GI pipe

    But i mean that what would be feasible or economical
    1- if i fill complete tank by a centrifugal pump through bottom/base inlet
    2- filling the complete tank from the top inlet
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  5. #4  
    Forum Professor jrmonroe's Avatar
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    It seems a matter of comparing pumping against the pressure at the bottom of the gradually-filling tank versus pumping against the pressure at the bottom of the always-full pipe. So we consider only pressures "at the bottom" of both the tank and the pipe.

    The pressure values at the bottom of the gradually-filling tank are always "less than or equal to" the pressure of the always-full pipe. So, the integration of the pressure of the gradually-filling tank is always less than the integration of the pressure of the always-full pipe. For example, compare summing the numbers up to 5 (ie, 1 through 5) to summing 5 five times (in this example, 15 compared to 25). Or summing the numbers up to 10 (ie, 55) compared to summing 10 ten times (100). Etc.

    An important concept Keep in mind that pumping into the the bottom of the tank is *not* working against the pressure of the *entire* tank, but only against a column of water in the tank that's the height of the water in the tank by the area of the pipe. Looking at it another way, part of the potential energy pumped into the water going up the top-filling pipe is then being wasted/converted into kinetic energy to make a waterfall.

    The summing of numbers up to x equals (x+x) whereas summing x for x times equals x. So where x grows infinite, the comparison (ie, (x+x) divided by x) approaches . As seen from the sums already given above, 15/25 = 0.60 and 55/100 = 0.55. So, when you chop the amount of pumped water into an infinite *number* of pieces, pumping into the bottom of the gradually-filling tank takes only half the energy of pumping up the always-full pipe.

    I played a little quick and dirty with the math in the previous paragraph, but I hope you followed along, or I can explain it a little more.
    dan hunter likes this.
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