Specific Speed

The impeller's rotational speed affects the capacity, efficiency, and extent of cavitation. Even if the suction lift is within permissible limits, cavitation can be a problem and should be checked. The specific speed of the pump is determined with the following equation:

Specific speed, Ns =

RPM X Capacity (gpm)

H3/4

Charts are available showing the upper limits of specific speed for various suction lifts.

FIG. 7.12.4 Role played by NPSH in determining allowable suction lift. A. Pump with suction lift. B. Pump with submerged

FIG. 7.12.3 Determination of pump discharge head requirements.

FIG. 7.12.4 Role played by NPSH in determining allowable suction lift. A. Pump with suction lift. B. Pump with submerged

FIG. 7.12.5 Typical pump curve for a single impeller.

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