Page 63 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

Fiaure 5-2
The graph (Figure 5-2) shows the useful work of a pump. Notice that
the pump pumps a combination of head and flow. As a general rule, as
flow increases, the head decreases.

Exam ple :
Given: Pressure or Head required = 100 feet at 200 gpm. What is the
water horsepower required for this pump? Assume a sp. gr. of 1 .O

H x Q
wHp= -- - 100 fi. x 200 gpm = 5.05 HP
3960 3960
If the specific gravity at pumping temperature were not equal to 1.0,
then the water horsepower would be adjusted by the specific gravity.

H x Q x sp.gr.
WHp =
3960

Flow determination

Flow is the number of gallons per minute that the pump will discharge.
rn Any pump will generate more flow as the discharge pressure is
reduced.
Equally, the pump will generate less flow as the discharge head or
pressure requirements are increased. Obviously, both flow and head
should be known before selecting a centrifugal pump.