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Homework Help: Ratio of water pump capacity to static header height

  1. Apr 15, 2015 #1
    1. The problem statement, all variables and given/known data

    800L/h rated pump 12.6mm outflow pipe.
    Static head height 1.10m
    There seem to be no undue turbulence in the flow.
    Environmental pressure is just atmospheric (1bar)

    2. Relevant equations


    3. The attempt at a solution

    I have done the physical experiments which is how I found the static height.

    Since first posting this question yesterday I have repeated the experiment and estimate at 0.9m elevation I have an effective flow rate of rate of 360L/hour.

    Google search yielded no formulas
  2. jcsd
  3. Apr 15, 2015 #2


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    There doesn't seem to be a question in the problem statement but I assume you are trying to calculate the "Ratio of water pump capacity to static header height"

    Edit: or rather the flow rate vs head height?

    Your post mentions three data points (two in the problem and one you measured). Have you considered a graph?
  4. Apr 16, 2015 #3
    Essentially my problem is that I want to know how much water is being delivered from a lower tank to a higher one.

    I can be confident of the static height (1.1m) but what I’m not able to be sure of is how much water is being delivered at lower elevations probably 0.9m.

    If I knew the formula to use I could design the system to give me the best compromise between height differential and flow rate (also for future reference).
  5. Apr 18, 2015 #4
    For 800L/h, this is the discharge of the pump or 0.0 m of head height. Now plot the points on a graph.
  6. Apr 20, 2015 #5


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    You have two data points from the specification...

    0L/H @ 1.10m head
    800L/h @ 0m head

    If you draw a straight line graph between those two points you will get a rough idea of the flow rate at other heads. However in reality the actual performance isn't usually a straight line. If you add the data point you measured (360L/h @ 0.9m head) you will find that is better than implied by the straight line graph.

    Ideally you would acquire a few more data points and plot a curve.
  7. Apr 22, 2015 #6
    Thanks for your advice I will do as you suggest . In my experiment I felt there mite be inaccuracies some that would flatter the LPH and some that would diminish the LPH figures e.g. the Ventura pipe that normally sucks air in to the outflow stream was acting as a pressure escape valve so returning water to the intake water container essentially pumping water around a closed system . It is probable that my approximation was over positive hence giving me a slightly optimistic value of 360LPH at 0.9M
  8. Apr 22, 2015 #7


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    Manufacturers data can be pretty inaccurate. Some will under spec their pumps to ensure the actual flow rate is always higher despite manufacturing tollerances and the like. If you need accuracy best set up the experiment as near as possible to the real world situation and measure it. Mains voltage can also vary quite a bit and that will effect flow rates on some pumps. As I recall the statutory limits in the UK are something like 220V -6%, +10%. The pump rates might be specified at a nominal 220V or 220V-6%.
  9. Apr 23, 2015 #8
    Thanks again for your advice.
    The purpose of the lower tank is to act as a sump/filter for the higher one, so effectively I really only need to know roughly how well it is doing, and of course there is the academic curiosity (witch I must admit would still like to see the formula even if I never use all or part of it e.g. Viscosity, turbulence etc.)
    There would be an overflow returning water to the lower tank so by design it will always be a self-balancing system
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