AN887
DS00887A-page 18
2003 Microchip Technology Inc.
Let us say that the user
wants a centrifugal pump for
water flow of 100 gallons/minute for a pressure head of
50 feet continuously and
occasionally needs a peak
flow of 200 gallons/minute. The curves of load and
pump are as shown in Figure 23. It can be observed
that for an occasional peak requirement of 200 gallons/
minute, the user is forced to go for an over designed
pump, which means
higher investment cost. Also, if
the pump is run directly with supply,
without any control
of flow, the pump continuously runs at a speed higher
than required. This translates into more power
input to
the pump (Affinity laws) and hence
a higher energy
bill. Also, the user does not have any control overflow.
For years, to control flow, the throttle value was imple-
mented. Closing this mechanical part partially, to regu-
late the flow, shifts the operating point
to the left of the
curve and increases the pressure head (as shown in
Figure 23). But it adds to
the frictional loss and the
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