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

188 Centrifugal Pumps: Design and Application
Figure 11-4. Brumfield performance criterion,
design considerations and that many details of inducer design are not addressed.
The angle /3 is the fluid angle at inlet and differs from the blade
angle, ft, by a positive incidence angle, a. Prerotation is assumed to be
zero, and other considerations such as blade shape, blockage, hub geometry,
and leakage are simply ignored. The intent here is primarily to show
the fundamental influence of the inlet blade angle on suction performance
potential.
Optimal inducer design is distinctly a high-tech endeavor which must
conform to hard-earned design guidelines and hydraulic disciplines. A
well-designed inducer should possess a "sharp" breakdown characteristic
as illustrated by the solid curve in Figure 11-5, rather than the "gentle"
curve shown in broken line. The NPSHR disadvantage with gentle
breakdown is evidenced by the NPSHR differential which exists at the
3% head depression level. It should not go unnoticed that the 3% head
depression level refers to the inducer-pump combination, so the level of
the 3% line on the inducer headrise curve will vary according to the head
of the pump to which the inducer is coupled. Lower head units will suffer
an NPSHR disadvantage with a gentle breakdown inducer compared to
high head units equipped with the same inducer.