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Fluid flow question through hose

  1. Sep 19, 2007 #1
    Here's a silly question.

    If I'm comparing two different sizes of hose, using the same flow rate in gpm, how do I calculate the pressure drops through each for comparison?

    I'm considering using hoses with interior diameter .438 and .688, each with a length of 5 inches.
  2. jcsd
  3. Sep 19, 2007 #2


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    I am assuming that you want to measure the delta P, not calculate it. Calculating it is basic stuff.

    If you are flowing to atmosphere on one end, you will have to adjust the pressure side of the pump you are using to get the flowrates to be equal between the two hose sizes. You can rely on a pressure gauge right at the outlet of the pump to give you the required delta P data.
  4. Sep 19, 2007 #3


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    Pressure drop depends on these items. The fluid density, fluid velocity, pipe (or hose) roughness, length of the pipe (or hose), diameter of pipe (or hose), and any elevation changes between the two ends.

    A standard equation for pressure drop is given by:

    delta p = ((pf*f*L*v^2)/(144*d*2*g)) + ((z*pf)/144)


    delta p = pressure drop in lbs/in^2
    pf = density of fluid in lbs/ft^3
    f = friction factor
    L = length in feet
    v = velocity of fluid in ft/sec
    d = diameter in ft
    g = gravitational acceleration in ft/sec^2
    z = elevation change in feet

    The friction factor, f, is found depending on whether the flow is laminar or turbulent. If you find that the flow is in the critical region (between laminar and turbulent, 2000 > Re < 4000), then emperical testing is more accurate.

    Hope this helps...

    Make sure your units are the same as shown above!
  5. Sep 22, 2007 #4
    look up Moody chart the rest is standard and described above. (find Re #)
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