Pumps - Specific Suction Speed

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Suction Specific Speed may be used to determine what pump geometry - radial, mixed flow or axial - to use for maximum efficiency and prevent cavitation. Suction Specific Speed is commonly used as a basis for estimating the safe operating range of a pump.
Suction Specific Speed is dimensionless and are expressed as

N_ss = ω q^1/2 / NPSH_r^3/4 (1)
where
N_ss = Suction Specific Speed
ω = pump shaft rotational speed (rpm)
q = flow rate capacity (m³/h, l/s, m³/min, US gpm, British gpm) at Best Efficiency Point BEP

NPSH_r = pump NPSH required at best efficiency point (m, ft)

Specific Suction Speed can be compared with Specific Speed but instead of using the total head of the pump, the available Net Positive Suction Head N.P.S.H._a is used.

As a rule of thumb the Specific Suction Speed should be below 8500 (calculated with US gpm) to avoid cavitation.