Abrasive Waterjet Nozzles: Jet Power

November 30th, 2009

Power at the Nozzle

Regardless of the size or type of pump or the size of its drive motor, the real measure of power output is the power at the waterjet nozzle. This is a direct function of the nozzle pressure and the volume flow rate through the nozzle, which can be expressed by the following formula:

HP = 0.58PQ


  1. HP equals the hydraulic power actually delivered through the nozzle in units of horsepower

  2. P is the water pressure at the nozzle in units of thousands of pounds per square inch  (for example, use 55 for 55,000 psi). This can usually be closely approximated by the pump output pressure, but watch out for systems that try to operate relatively large nozzle orifices (say greater that 0.014”) using relatively long runs of ¼” ultra-high pressure tubing with many fittings.  The pressure drop between the pump and the nozzle for such systems can be several thousand psi.
  3. Q is the volume flow rate through the nozzle, in units of gallons per minute
  4. The constant of 0.58 accounts for the units of measure being used in the equation.

This simple equation makes two things very clear:

  1. The size of pump motor and the exact design and brand of pump are not in the equation.  All that really matters in determining true nozzle power are the nozzle pressure and the volume flow rate
  2. Both pressure and volume flow rate are in the equation and have equal effect.  Power at the nozzle can be increased by increasing pressure or increasing volume flow rate or a combination of both.

So the next time you are trying to compare ultra-high pressure pumps, ignore the size of the drive motor shown on the manufacturer’s spec sheet.  Go further down the spec sheet and find the values of the recommended continuous operating pressure and the corresponding output volume flow rate.  Then grab your calculator and determine for yourself the actual effective output power.

Best regards,

John Olsen

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  1. December 8th, 2009 at 17:50 | #1

    Very handy information, thanks.

  2. January 2nd, 2010 at 14:01 | #2

    Hello Dr. Olsen,
    Your website/blog page is very nice. Very informative and glad to see your innovative talents push the manufacturing industries.
    It is great to see the evolution continue.

  3. Leo
    October 20th, 2010 at 21:12 | #3

    I am wondering if this technology could be used to cut the hardest stone (in lieu of diamond tip saw) and portable enough to carry in the mountains?

  4. October 19th, 2011 at 03:55 | #4

    Leo, Not sure if you found the answer you were looking for?

    Water Jet cutting machines are not portable, i believe you could use a water jetting machine (water blasting) with an abrasive nozzle fitted (if cutting by hand) or there are other accessories that i’ve seen that can attach to cut steal without the operator being close. Water jetting machines can be trailer mounted if you have road access close to your location. You could then run the hose’s to your cutting location. Hope that helps

  5. Dr Olsen
    November 1st, 2011 at 12:47 | #5

    Precision water jet cutting machines are not portable as stated, but for crude work you might consider a water blasting machine normally used for high pressure cleaning. Fit it with an abrasive nozzle and have at it. The water blasting people have also developed various mechanical nozzle carrying devices that may be of use to you. Check with the company “Stone Age” in Colorado. Emphasize safety and follow all the safety precautions for water blasting. The WJTA has a good safety manual for hand held water blasting equipment that should be followed.

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