Jeff Spitzer wrote:

In many cases of water pump power you will find that it's hard to

make the

numbers add up.  I'll tell you why.  Most of the horsepower goes into the
bearings and seals.  If you do the math you find that 35-40 GPM at 15 psi
or whatever you think the loop drop is amounts to only fractional
horsepower.  Now take the pump in your hand and estimate the frictional
torque of the seals.  Now multiply that torque times 10K RPM or whatever
the pump is spinning.  You'll find that it amounts to more power.  If I

had

to guess I'd say the pump itself uses around 1 hp and the seals and
bearings accounts for a couple more.

Jeff Spitzer

Jeff,

Bill Freeman wrote:

Do these pumps us a ceramic face seal like and industrial pump?

Yes, typically a face seal keeps the water in.  There are also 2 lip seals
to keep grease in the bearing cartridge.

 I have

never disassembled one, and always just assumed (you know what that
means!) that they used a rubber lip seal like a crank oil seal.  I have

never

measured the torque consumed in a lip seal, but it seems as if a rubber
lip seal was absorbing even a fraction of a hp it would be toast in about
10 minutes.

I agree, except for the presence of coolant as you point out.

Must be a face seal (ceramic faces in plane perpendicular

to shaft CL, axial spring, mirror finish) and cooled with coolant flow.
Interesting.  Never considered that the seal could eat up that much HP.
Our water pump at our house in Fla years ago had a 1/4 - 1/2hp electric
motor and used this sort of face seal, so it is weird that they would

consume

so much HP in a car.  I'd imaging that the house pump put out about
5 -10 GPM and raised the water about 30 ft ("jet pump" -ejector actually),
and probably had 30-40 psi output pressure.

Let's see, assume 15 psi for the head + 40 psi for the outlet pressure,
at 5 GPM, you have 0.66 cu ft/minute = 41.7 lb/min with an equivalent
lift of about 120 ft which is 5004 ft-lb/min divided by 60 = 83 ft-lb/sec
divided by 550 ft-lb/sec = 0.15 hp.  So a quarter hp motor will drive it,
without any seal power consumption.  Hmmm.

35 GPM at 15 psi will be 4.675 cu ft/min X 62.4 lb/cu ft = 292 lb/min
The 15 psi is equivalent to a 33 ft lift,  so 292 x 33 = 9636 ft-lb/min
divided by 60 = 160.6 ft-lb/sec divided by 550 = 0.292 hp.
Even assuming a low value like a 30% efficient impeller, you don't
reach one HP.

Amazing.  Never have looked at auto water pumps before.  I spent
most of my youth playing with VWs and Porsches, and now airplanes.
Have actually only replaced a single water pump and didn't really look
at it much.  Learning.

Bill

If you do the math like your example for a water pump and then try to drive
it with a small motor (as calculated) it doesn't work.  All that excess
power has to be going somewhere and there ain't many choices.

Jeff Spitzer

 
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