Page 62 - Know and Understand Centrifugal Pumps

Useful Work and Pump Efficiency

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10 Pounds
~
I I I I

Feet
I
I
I I I

-c+ 10 Pounds

Figure 5-1
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550 fi.-lbs./sec.). This is the reason that even today, all motors,
whether steam, internal combustion engines, boilers, electric motors,
gas turbines, and even jet and rocket engines are rated in Horsepower,
and not Ostrich power or Iguana power.
We say that the motor generates horsepower (HP), and that the pump
consumes brake horsepower (BHp). The difference between HP
(output) and BHp (input) is what is lost in the power transmission; the
bearings, shaft, and coupling between the motor and the pump.
We say that the usehl work of the pump is called Water horsepower
(WHP). It is demonstrated mathematkall; as:

H x Q x sp.gr.
WHp =
3960
Where: H = head in feet generated by the pump Q = flow recorded
in gallons per minute sp. gr. = specific gravity
3960 = constant to convert BHp into gallons per minute
Horsepower x 60 sea. / min.
3960 =
Weight of 1 gal. of water

550 lbs. ft / sea. x 60 sea.
3960 =
8.333 lbs. / gal.
If the pump were 100% efficient, then the BHp would be equal to the
WHp. However, the pump is not 100% efficient so the BHp = WHp x
efficiency, and the formula is:

H x Q x sp.gr.
BHp =
3960 x eff.

45 F1