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

68 Centrifugal Pumps: Design and Application
Figure 6-2. Multi-stage pump stage arrangements.
throat to the suction of the next stage imparts a spiral motion to the flow
resulting in prerotation and hydraulic losses. For these reasons, the
multi-stage pumps of 25 or more years ago were designed with high looping
crossovers. To achieve radial balance these crossovers were in both
the top and bottom casing halves. This design, referred to as the "pretzel"
casing, was very costly, difficult to cast, and limited to a maximum
of eight stages.
These problems prompted a study to evaluate the performance of various
crossover shapes. A 4-in. pump delivering 1,200 GPM at 3,550
RPM was selected as a model and the three crossover configurations
shown in Figure 6-3 were tested. For these tests the pump hydraulic passages
were highly polished (60-80 micro-inches), ring clearances were
minimized and component crossover parts were carefully matched using
a template. Configuration 1 was designed with a total divergence angle of