Page 139 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

liquid from a common system, and discharging the liquid into the same
common system. Two pumps running in parallel offer twice the flow at
the same head. Pumps in series are two or more pumps where the
discharge of one pump feeds the suction of the next pump in series.
Two pumps running in series offer twice the head with the same flow.
And the combination of the two arrangements offers up to multiples of
both factors. First let’s consider the arrangement of pumps in parallel.

Pumps in parallel
~~
The system is designed so that two equal pumps are operating together
side by side. The system can support the production of both pumps. If
the needs of production are reduced, this system can operate with only
one pump, simply by removing one pump from service (Figure 8-25).
The curves of pumps ‘A’ and ‘B’ individually, and ‘A and B’ in parallel
are seen in Figure 8-26.
Because the system is designed for both pumps running together in
parallel, the system curve appears as shown in Figure 8-27.

Here we see something interesting. Because the system is designed for
both pumps running in parallel, when only one pump is operating, this
pump will run to the right of its BEP. This situation brings it’s own
peculiar set of implications, not often understood in industry.

Figure 8-25

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