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NPSH Required (NPSHr)

The minimum suction head the pump needs at its inlet to avoid cavitation — derived from speed, flow and suction specific speed.

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rpm
m³/h
Flow per impeller is Q ÷ i for double-suction pumps.
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From the pump datasheet; ~8,500–11,000 is a typical process range.

Result

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Method & assumptions
NPSHr = [ N · √(Q ÷ i) ÷ Nss ]4/3

Suction specific speed defined as Nss = N·√(Q/i) ÷ NPSHr0.75 — rearranged for NPSHr. Field-unit convention (Q in m³/h, head in m). A higher Nss for a given duty means the pump needs more suction head.

Engineering aid only — verify results against the applicable code edition and the equipment datasheet before committing to a design.

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