Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

258 Centrifugal Pumps: Design and Application
Figure 14-7. Comparison of pump and turbine characteristics at constant
speed. Characteristics are the percent of pump best efficiency values taken as
100%.
Because of the higher capacity throughput and higher differential pressure,
the HPRT power output is greater than the power requirements of
the pump. Subsequently, the higher shaft stresses result in speed limitation
unless the allowable stress or diameter of the shaft has been increased.
If a multi-stage pump is selected to operate as an HPRT, a heavier shaft
can be installed, since most pump manufacturers build their multi-stage
pump line with standard and heavy-duty shafts because of a larger number
of stages, higher specific gravities, or high-speed applications. Single-case
pumps are limited to the maximum pressure they can withstand.
For high-pressure HPRT applications, either the allowable maximum
working pressure of the pump case has to be increased or a double, or
"barrel-type," case has to be selected. Barrel-type cases are also used for
high-energy and low-specific-gravity-type HPRT's.
Another important check is evaluating the adequacy of the bearing design.
Depending on specific speed, some pumps when operating as
HPRT's at the same speed will have twice the differential pressure and