Page 137 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

H SECONDARY
FEET

H2 PRIMARY

H BEP

H1

0
0 Q2 Q Q1 Q
BEP GPM
Fiaure 8-22
On superimposing the curve of a single pump over this system curve,
we see that the system extremes are too wide for the pump to cover on
its curve (Figure 8-22).

You should install pressure sensors that transmit a message to shut-off
the pump, sound an alarm, or indicate to the operator that the moment
to change the filter has arrived. With a new filter installed, the pump
begins operating again to the right of the BEP within the sweet zone
and slowly over time proceeds moving toward the other end of the
sweet zone.

Pumps in parallel and pumps in series

Up to this point we’ve considered dynamic elements in the system with
other elements static. There are times, and systems where everything is
moving in concert together, with elevations rising and falling, variable
pressures, clogging filters, and control valves opening and closing.
When the entire system is dynamic, you’ve got to determine the elev-
ation extremes, the pressure extremes, and the resistance extremes. The
totally and completely dynamic system appears as Figure 8-23 and
Figure 8-24.
When this happens, you need to consider an arrangement of pumps
running in parallel, or in series, or in a combination of the two. Pumps
in parallel are two or more pumps working side by side, taking the