If I need to get a pressure of 6 bar at the exit of a nozzle for cleaning purpose, how can I determine the following (assuming nozzle outlet dia to be 5 mm):

  • The pump capacity to provide such a pressure.
  • The diameter of pipe connecting pump to nozzle assuming total 5 m length.

I'm not looking for mathematically precise answers, but just need to get overall idea of how to calculate the pump and connection specifications.

Some additional information:

  • The working fluid is water.
  • The nozzle is used to clean a plate which would be kept at distance of 200mm from the nozzle exit.
  • The working pressure is specified as 6 bar, which I believe is the stagnation pressure at the nozzle exit.
  • The nozzle dia is 5 mm
  • 2
    $\begingroup$ The pressure at the exit of a nozzle is equal to the ambient pressure (typically atmospheric pressure) unless the flow is supersonic, in which case the pressure drops across a shock wave outside the nozzle. Can you provide some more information about what you're trying to do, and where the 6 bar came from, what the fluid is, what the required flowrate is, etc.? $\endgroup$ – Mark Aug 18 '16 at 10:12
  • $\begingroup$ Also, the nozzle type is something you must consider. $\endgroup$ – F.Bek Aug 18 '16 at 10:35
  • $\begingroup$ Thanks for the comments and suggestions, I have made the necessary edits in the original question. $\endgroup$ – Harry Aug 19 '16 at 6:49
  • $\begingroup$ Sounds like the 6 bar is the pressure at the nozzle inlet. You need a pump that will deliver 6 bar pressure plus enough to overcome the pipe losses. But you still need to know the flow rate to size the pump. The nozzle specs should tell you the flow rate as a function of inlet pressure. $\endgroup$ – Mark Aug 19 '16 at 9:44
  • $\begingroup$ Flow rate and pressure are both critical parameters needed to determine the pump performance. $\endgroup$ – geekly Jul 31 '17 at 14:53

If you know the specifications (pipe smoothness) of the pipe, then you can use the Darcy-Weisbach equation to calculate the pressure drop of the water across your 5m pipe. It is as follows:

$$ \Delta P = f \frac{L}{D} \frac{\rho V^{2}}{2} $$

Where P is your pressure, f is the friction factor, L is the length of your pipe, D is the diameter, rho is the density of water and V is the flow velocity.

Then you can use the pump duty equations in order to work out what power your pump needs to be in order to deliver 6 bar at the nozzle at your required velocity.

| improve this answer | |
  • $\begingroup$ Note that the friction factor, f, varies with velocity - specifically through the Reynolds number. See here for more information en.m.wikipedia.org/wiki/Darcy_friction_factor_formulae $\endgroup$ – Mark Aug 20 '16 at 12:44
  • $\begingroup$ Correct. Depending on whether or not you have laminar flow, your friction factor will vary. I believe for laminar flow, it is simply 64/Re, but for turbulent flow you should consult a Moody diagram. $\endgroup$ – Georgeos Hardo Aug 20 '16 at 12:45

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