Page 211 - Centrifugal Pumps 2E
P. 211

High Speed Pumps     189





























                       Figure 11-5. Inducer characteristics curves.





           Commercial inducers have tended to result in performance suction spe-
         cific speeds on the order of S s = 20,000 to 24,000. This level of perfor-
         mance entails some compromise from the standpoint of consideration of
         inducer cavitation but provides respectable inducer design, though per-
         haps not ultimate design. These suction specific speeds generally
         produce dramatic improvement in suction performance, frequently pro-
         viding up to 80% NPSHR reduction over uninduced pumps.
          Freedom from long-term cavitation erosion to the inducer itself is pro-
        vided by observing experimentally established cavitation limitations in
         the inducer design. The cavitation limitation is related to tip speed, fluid
         specific gravity, and the inducer material as follows:






        where K is an experimentally established constant which varies with the
        inducer hydraulics and material of construction.
          Commonly used 316 stainless steel is considered to possess "good" re-
        sistance to cavitation erosion, but exploitation of materials with superior
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