Calculating water pressure

  1. Given only the rate of flow in gpm and the inside diameter of a hose in inches, is it possible to calculate the pressure of water leaving the hose?
    I have no experience or training in this area but it seems to me that more information would be required. Any help will be greatly appreciated.
  2. jcsd
  3. it's been a while, but i believe that Bernoulli's equation could help. Check that one out
  4. Chi Meson

    Chi Meson 1,767
    Science Advisor
    Homework Helper

    Without getting into very advanced fluid dynamics, it is assumed that the water pressure, after the water has left the hose, is same as atmospheric pressure.

    If you are referring to the pressure of the water against a surface (as the water splashes on a surface like your hand, after it leaves the hose) then the "pressure" would be the force of the water/cross-sectional-area of the water stream (assumed to be the area of the hose?) P=F/A

    From the volume flow rate (gal/min) you can calculate the "mass-flow rate" (mass/sec), and assuming all the water is stopped, the mass flow rate times the change in velocity will produce the force.
    Ft = m[delta]v , so F=(m/t) x [delta]v

    So, yes, the pressure of this stream of water against a surface can be calculated from the information given.
    Last edited: Oct 26, 2004
  5. I am trying to calculate the force exerted on a body during high pressure water blasting. The numbers are 36,000psi pump pressure, 5gpm flow rate. lbs of force back pressure is the number I'm looking for. HELP!
  6. russ_watters

    Staff: Mentor

    You need the velocity, then you use Bernoulli's equation to find the pressure. What is the area of the nozzle?
  7. There are two nozzles. Both are 1/8" in diameter.
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