Page 167 - Centrifugal Pumps Design and Application

144 Centrifugal Pumps: Design and Application

Figure 10-5. Pump performance for initial and ultimate condition.

Another method of satisfying two capacities at optimum efficiency is
the installation of volute inserts. These removable pieces reduce the in-
ternal fluid passages and physically convert a high-capacity pump to low
capacity (Figures 10-9 and 10-10). Inserts of this type are ideal for low-
capacity field testing or reduced throughput operation with improved ef-
ficiency (Figures 10-11 and 10-12).
Destaging

It is not unusual for pipelines to start up at low pressure then later
change to high pressure at constant throughput. This change in pump
head requirements can be suitably handled by selecting a multi-stage
pump for the ultimate high-pressure condition. For the initial low-pres-
sure condition, appropriate impellers are removed and the interstage
chambers isolated by destaging tubes (Figure 10-13). When changing to
high pressure the destaging tubes are removed and additional impellers
installed (Figure 10-14).