Pump Specific Speed and Impeller Type

Ns = N sqrt(Q) / H^(3/4) (rpm, gpm at BEP, ft per stage) classifies the wheel - radial below ~2,000 (high head, low flow, the building-service norm), mixed flow ~2,000-4,500, axial above ~4,500. An 1,750 rpm pump at 500 gpm and 100 ft runs Ns 1,237 (radial); drop the head to 25 ft and Ns jumps to 3,500 (mixed flow) - the head-to-flow ratio, not the size, sets the geometry. US dimensional form; the suction specific speed Nss is separate. An engineering aid; the manufacturer's curves govern.

Ns = N sqrt(Q) / H^(3/4) (N rpm, Q gpm at BEP, H ft per stage); class = radial < 2,000, mixed <= 4,500, else axial.

The US pump specific speed Ns = N sqrt(Q) / H^(3/4) and the customary impeller-type bands, as compiled in the Hydraulic Institute and pump-handbook references, by name.

The specific-speed definition and the impeller-type bands are public results in the standard pump references.

Estimate. AHJ and licensed professional govern.

Field names used by the API: n_rpm, q_gpm, h_ft, ns

• Specific speed Ns = N sqrt(Q) / H^(3/4) at BEP, per stage (US dimensional form)Hydraulic Institute
• Impeller bands radial below ~2,000, mixed flow ~2,000 to 4,500, axial above ~4,500pump-handbook convention
• Per stage divide total head by the number of stages before applyingpump design practice