Page 101 - Know and Understand Centrifugal Pumps

Know and Understand Centrifugal Pumps

H
Feet

0 -

a
GPM
Figure 7-9 -
~~~ ~ ~~
Avoid zones ‘C’ and ‘D’ at all times. The pump can be operated in
zone ‘B’ only if it is necessary.
Zone ‘B’ is slightly to the left of the BEP. At this point the pump and
impeller is slightly over-designed for the system. The pump will suffer a
loss of efficiency. Radial loading is generated on the shaft that can stress
the bearings and seal and may even break the shaft. If it is necessary to
operate the pump in this part of its curve (to the left of the BEP), for
more than a few hours, you should install an impeller with a reduced
diameter. Remember that the back pullout pump exists for rapid and
frequent impeller changes (see Chapter 6). By reducing the impeller
diameter, you can maintain the head and pressure, but at a reduced
flow. Figure 7-10 illustrates this point.

In zone ‘C’ the pump is operating to the right of the BEP and it is
inadequately designed for the system in which it is running. To a point

Original Dia.

Reduced Dia.
/H
Head
remains
the same

0 - -
Q Reduced Q Original Q
GPM
Fiqure 7-10