Suction-Specific Speed

A formula that predicts one of the types of cavitation. Pumps should be purchased with a number below 8500 (9883 in metric units, m³/h). The formula for suction-specific speed (N_SS) is:

For US Units:

N is pump speed, rpm; Q is pump flow in gallons per minute, at best efficiency point, per impeller eye (for double-suction impellers divide total pump flow by two); NPSH_r is pump NPSH required in feet at the best efficiency point.

For Metric Units:

N is pump speed, rpm; Q is pump flow in liters per second, at best efficiency point, per impeller eye (for double-suction impellers divide total pump flow by two); NPSH_R is pump NPSH required in meters at the best effiency point.

Use the following relationships to convert N_SS values between those with imperial units (gpm), metric units (m³/h, L/s) and vice versa:

N_SS (US gpm) = 1.63 N_SS (metric L/s) = 0.86 N_SS (metric m³/h)

N_SS (Metric L/s) = 0.614 N_SS (US gpm)

N_SS (Metric L/s) = 0.67 N_SS (British gpm)