Electrical HP required for hydraulic pump

Macke,

To determine a pumps horsepower use the following equation:

Pump Horsepower (P) = QHS/3960U

Where:

P = Power, hp
Q = Flow Rate, gpm
S = Specific Gravity of fluid
H = Head height, ft
U = Efficiency coefficient

So, what we need to ascertain is the specific gravity of the fluid you plan to use as the hydraulic working fluid.

Macke,

I would think that they would be similar. That is, the pump horsepower and the horsepower of the prime mover needed should be very close. The only difference would be whatever the pump and motor bearing friction adds to the needed horsepower. I wouldn't think you'd have a problem figuring pump horsepower, then dividing it by your .85 efficiency and adding, say 10%, you'd probably be close enough. Also, as I'm sure you are well aware, hydraulic pumps aren't always doing work all the time. They only work in a valve or other component in their system repositions. Unless, of course, you are actually running something with a hydraulic motor. Sorry that I misunderstood your question. Maybe I've been of no help. Good luck.

Codey-- you are PRECISE!

BUT THAT IS HARD shock to some . Poor fellow wanted to make do with 3 HP!

What I meant was: If he has a 'Cont Rated 30 Kw ' 2 pole @ 60Hz=~3500rpm motor he can with difficulty get some tough job done for a couple of minutes--at 160% torque with some 20% slip from synchronous.Just about.

If he plans a new low power installation, he will be well advised to use a 4 Pole ~1720rpm Motor ,Nameplate rated '20Kw Continuous duty'.Again -penny pinching!

If he has to run a high speed Hyd. Press or such-- no under-rated drive would do.

100HP Cont. Duty@3520RPM That'll be his new motor.

But I suggest he reviews his real need and the health of his HYD pump -- which he mentions being "Iron Body".

figure on hydraulic oil having specific gravity of 0.85 (about 7.5#/gal) and you will be 'golden' .

use pump efficiency of 0.85, motor efficiency of 0.9, and service factor of 1.15

gpm x (psi/14.7) x(34.3 x7.5)=ft-#/min of fluid work (A)

A/33000 = fluid Hp at 100% efficiency (B)

(B/(pump eff x motor eff) = motor Hp (C)

C x serv factor = connected load in Hp.

Hello Keith, couple of comments.

Only need to take account of fluid SG if head in ft of fluid is specified. If pressure difference, psi is given as here, SG doesn't come in.

Also, after working out the pump shaft power (from fluid power and pump efficiency) that gives the motor rated power. No need to divide by motor efficiency, rated power is shaft output power. Dividing by motor efficiency gives electrical input power.

Service factor I would say is optional, depending how much safety you want and how much confidence there is in the inputs to the calc.

Cheers.....Codey

I think you may have miss-interpreted the question. It is not the Hp of the pump that he requires. It is the Hp to drive the pump. Unusually the guy HAS given all the required information to calculate. All you need is the Flow Rate and the Max Pressure Required.

Specific Gravity of the fluid and Head height (although important) all become a component of Max Pressure in the system so, in this case, can be ignored in the calculation. Also, the efficiency coefficient (of the motor and the pump combined)is added after.

See #7

Hope this clarifies!

General "Rule of Thumb" is 1 gpm @ 1000psi requires 1 horsepower. Has worked well for me for thirty years.

Regards CEKM

To calculate motor Hp required (in kW), the basic calculation is as follows (in metric units)

Pressure (in Bar) * Flow (Lts/min)/600

This gives:-

173*196 / 600 = 56.51kW

If you include for an efficency factor of 80% you will require a motor of 70.64kW (70kW).

I hate gpm as we never know if it's UK or US flavour. I have gone back to your cu.in to calculate.

I have worked many years overseas and aboard foreign built ships, I have become accustomed to the Metric system, I like it and have difficulty understanding why the Americans are the only remaining major country in the world that still use the British Engineering System, not even the British still use the BES. We Americans are so provincial, we can travel 3000 miles in any direction and still speak English. Because of my travels and overseas assignments I have become conversant in three languages besides English, and say a few words in at last count 25 languages. Wake up Americans, this is now a global world.

Sorry to get on my soapbox, but I still have to use GPM and Horsepower, I would rather use Liters or Kilograms per minute and KW.

Regards CEKM

So when somebody talks to you about GPM are you always so sure (and being American) that you assume American Gals/min. Thankfully are friend who posed the question included cu.in. I can never understand why the Americans bastardised a Gallon! Lets all go metric tomorrow (please)!

Strange thing is that I actually still prefer psi.

I know this topic is a few years old now but there is one thing that I believe has been overlooked with this question. The pump itself has not been detailed. You will only need the full 3625 psi for a small portion of the time for most applications. A ram for example will only need full pressure at full load. So if you are only moving the ram up and down you will not need a lot of pressure to do it. The reason I bring this up is that a lot of hydraulic pumps are multi stage and have high flow rates at low pressures and then low flow rates at the higher pressures. I built a 100 tonne press a while ago and I was able to use an 11 gpm pump and .5 gpm pump in tandem with some isolation between pumps. With these 2 pumps I could achieve 8000 psi with only 6 hp to drive the thing. If you looked at this question again and took into account the properties of the pump and it's intended behaviour in use you could get away with a lot less horsepower to get the job done. Sure it would slow down when you put it under load but I feel safer with a press that does slow down especially at 100 tonne.