Specific Speed - Pumps

Specific speed may be determined independent of the pump size

Specific Speed is a number characterizing the type of impeller in a unique and coherent manner. Specific speed are determined independent of pump size and can be useful comparing different pump designs.

  • Specific Speed identifies the geometrically similarity of pumps

Specific speed can be expressed as

Ns = ω q1/2 / h3/4         (1)

where

Ns = specific speed

ω = pump shaft rotational speed (rpm)

q = flow rate (m3/h, l/s, l/min, m3/min, US gpm, British gpm) at Best Efficiency Point (BEP)

h = head rise (m, ft)

Online Specific Speed Pump Calculator

The calculator below can used to calculate pump specific speed:

ω - pump shaft rotational speed (rpm)

q -  flow rate (m3/h, l/s, l/min, m3/min, US gpm, British gpm)

h = head rise (m, ft)

Note! When comparing pumps and their documentation be aware of the units used.

Typical values for specific speed - Ns - for different designs in US units (US gpm, ft)

  • radial flow - 500 < Ns < 4000 - typical for centrifugal impeller pumps with radial vanes - double and single suction. Francis vane impellers in the upper range
  • mixed flow - 2000 < Ns < 8000 - more typical for mixed impeller single suction pumps
  • axial flow - 7000 < Ns < 20000 - typical for propellers and axial fans

Convert between US units (gpm) and Metric units (m3/h)

  • Ns(US gpm, ft) = 0.861 Ns(m3/h, m)
  • Ns(British gpm, ft) = 0.787 Ns(m3/h, m)

when

  • 1 US gpm = 0.2271 m3/h
  • 1 British gpm = 0.2728  m3/h
  • 1 ft = 0.3048 m

Example - Specific Speed for a Pump - with different units

A pump has the capacity 1500 US gal/min (1249 British gpm, 340 m3/h, 94.4 liters/min) at 100 ft (30.5 m) of head and is rotating at 1760 rev/min. The pump specific speed can be calculated as:

US gpm, ft

Ns(US gpm, ft) = (1760 rev/min) (1500 gal/min)1/2 / (100 ft)3/4

    = 2156

British gpm, ft

Ns(British gpm, ft) = (1760 rev/min) (1249 gal/min)1/2 / (100 ft)3/4

    = 1967

m3/h, m

Ns(m3/h, m) = (1760 rev/min) (340 m3/h)1/2 / (30.5 m)3/4

    = 2500

liter/min, m

Ns(liters/min, m) = (1760 rev/min) (94.4 m3/h)1/2 / (30.5 m)3/4

    = 1317

Related Topics

  • Pumps - Piping systems and pumps - centrifugal pumps, displacement pumps - cavitation, viscosity, head and pressure, power consumption and more

Related Documents

Key Words

  • en: specific speed pump fan
  • es: ventilador bomba de velocidad espec√≠fica
  • de: bestimmten Geschwindigkeit Pumpe Fan

Search the Engineering ToolBox

- "the most efficient way to navigate the Engineering ToolBox!"

Engineering ToolBox - SketchUp Edition - Online 3D modeling!

3D Engineering ToolBox - draw and model technical applications

Engineering ToolBox - SketchUp Edition - add standard and customized parametric components - like flange beams, lumbers, piping and more - to your SketchUp model - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro. Add from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!

close