Forums » Electrical Engineering

kW for the motor of the pump

    • 25 posts
    January 11, 2020 10:06 AM PST

    I have seen someone has used to find out the kW for the motor of the pump.

    kW = (H x Q) / Pump Eff x 367
    motor power = p abs x motor eff

    where H is in meter
    Q = m3/hr

    Is this correct formula?

    • 75 posts
    January 12, 2020 7:44 AM PST

    Reference: Cameron Hydraulic Data, 1998

    I am a US Customary Units kind of guy.  So bear with me on a bit of confusion from that.

    Pump Hydraulic power = Delta(P) x Q


    Delta(P) = differential pressure across the pump, units are Newton/(meters^2)

    Q = Volume, units are meters^3/second

    Hydraulic power = (Newtons/meter^2) X (meters^3/second) = (Newton-meters)/second = Watts

    Of course, to get electric power input to the motor, one would divide by the pump eff, and divide by the motor eff.

    And Meters^3/second = Meters^3/(hour x 3600), and divide by 1000 to get KW.


    So, I don't know where the "367" comes from.

    Unless it was a mis-type: 

    kW = (H x Q) / (Pump Eff x (3.6 x 10^6))

    motor power = p abs / motor eff, where "p abs" = mechanical input to the pump shaft

    And, I am thinking it is highly likely you already knew all this.

    So, what is the context?

    • 25 posts
    January 12, 2020 8:46 AM PST

    Thanks Carl, I have farther searched and finally found the following

    P = p1 x g x Q x H

    expressed in kW

    P = g x Q x / 1000 kW

    Q is in liter/s
    H is in meter
    p1 is in Kg/dm3


    P = Q x H / 367 kW

    where Q is in m3/hr
    H is in m
    P is in kW
    367 is the conversion factor


    • 25 posts
    January 12, 2020 8:48 AM PST

    Just a tip

    367 = 3600 (s/h) ÷ 9.81 (m/s2)

    • 75 posts
    January 12, 2020 10:16 AM PST

    Ahhhh, yes.  Gravity snuck in there.  I would not have seen that without your tip.

    Did your original post list "where H is in meter"?  I'm surprised I missed that.  "H" would then be head, and the specific gravity is needed to get the pressure, which of course requires the gravity acceleration constant.  Sloppy me for missing that.

    So, p1  is a specific gravity = Kg/dm3, kilos/cubic-meter. What is the "d"?

    • 25 posts
    January 12, 2020 11:21 AM PST

    d = decimeter

    • 71 posts