NPSHR and Impeller Diameter
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Prior to computerized software for pump selection, manufacturers simply drew one NPSHR curve for the pump on the head versus capacity curve. It was used regardless of the impeller diameter chosen. This is not a good idea for the smaller diameter selections.
NPSHR for a fixed flow rate is less for the larger diameter impeller than the smaller diameter impeller. Or stated in another way, at a given flow rate the NPSHR increases as the diameter of the impeller decreases. (Note the head changes but the flow rate remains at some fixed value.)