## 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

Where:

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

OR

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
January 12, 2020 2:50 PM PST