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Controlling fluid Flow under pressure?

  1. Sep 2, 2013 #1
    this is not a homework problem, its a practical problem for a system i'm working on, but its looks pretty much like a homework problem so posting here.

    1. The problem statement, all variables and given/known data

    Assume a 100 gallon tank is filled with water, constantly filled and pressurized by a pump to 1000psi

    Assume a hydraulic powered motor which operates with intake required at 300psi, flow of 10 gallons per minute.

    Can the problem of stepping down the pressure and fixing the flow at 10 gallons per minute be solved by having a pipe connecting the tank to the motor of a given diameter, or a valve at the tank end, where the pipe is of fixed diameter, say 1"? The tank and the and motor are in close proximity, the pipe can be set to the length required.

    How generally to determine the diameter required? Is the length of the pipe relevant? Or is there some other step required to fix both the pressure and flow between the tank and motor?



    2. Relevant equations

    No sure.

    3. The attempt at a solution

    Flummoxed.

    I assume there is a relationship between pressure in the pipe and resistance to flow provided by the hydraulic motor. I know I can adjust raise pressure in the pipe by opening the value at tank end and/or using a smaller diameter pipe, but I'm not sure how/if its possible to control both pressure and flow independently as I'd guess they are related as in electricity flow, viz V=IR which in this case I'd guess would be something like pressure = flow x resistance, or Flow = Pressure/Resistance or something like that, but not really sure of units and the like.
     
    Last edited: Sep 2, 2013
  2. jcsd
  3. Sep 3, 2013 #2

    CWatters

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    Fluid dynamics isn't my area of expertise but there are pressure drop calculators around on the web. They might allow you to calculate the length and diameter of pipe required to drop 700psi at 10gpm. However if you then load up the hydraulic motor so that the flow rate through it is lower then 10gpm the pressure will rise. For example if you stall the motor so there is zero flow you might see 1000psi at the motor (no pressure loss in the pipe).
     
  4. Sep 3, 2013 #3

    CWatters

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    PS Perhaps look at controlling the pump that's pressurising the tank?
     
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