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Specific Speed Pump Fan

Reference data and engineering information about specific speed pump fan for fluid mechanics applications.

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Overview

Engineering reference data for Specific Speed Pump Fan in fluid mechanics.

Key Formulas

Reynolds Number

Re=ρvDμRe = \frac{\rho v D}{\mu}

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

P+12ρv2+ρgh=constP + \frac{1}{2}\rho v^2 + \rho g h = \text{const}

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

A1v1=A2v2A_1 v_1 = A_2 v_2

Conservation of mass for incompressible flow.

Darcy-Weisbach

ΔP=fLDρv22\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}

Pressure drop due to friction in a pipe.

Variables

SymbolDescriptionUnit
ReReReynolds number—
ρ\rhoFluid densitykg/m³
vvFlow velocitym/s
DDCharacteristic dimensionm
μ\muDynamic viscosityPa·s
PPPressurePa
ffDarcy friction factor—

Specific Speed Classifications

Pump designs can be classified by their specific speed values. The following ranges apply when using U.S. units (US gpm, ft):

3 rows
Typical specific speed ranges for different pump designs
Pump Type
Ns Range (US units)
Description
Radial Flow500 < Ns < 4000Centrifugal impeller pumps with radial vanes — double & single suction. Francis vane impellers in the upper range.
Mixed Flow2000 < Ns < 8000More typical for mixed impeller single suction pumps.
Axial Flow7000 < Ns < 20000Typical for propellers & axial fans.

Source: engineeringtoolbox.com

Unit Conversion Factors

Specific speed values depend on the unit system used. Use these conversion factors to compare values across different conventions:

2 rows
Specific speed unit conversion factors
Conversion
Formula
US gpm, ft → m³/h, mNs(m³/h, m) = Ns(US gpm, ft) / 0.861
British gpm, ft → m³/h, mNs(m³/h, m) = Ns(British gpm, ft) / 0.787

Source: engineeringtoolbox.com

Underlying unit equivalences used in these conversions:

  • 1 U.S. gpm = 0.2271 m³/h
  • 1 British gpm = 0.2728 m³/h
  • 1 ft = 0.3048 m

Hydro-Power Turbine Specific Speed

Specific speed is also used to characterize hydraulic turbines. Typical ranges are:

3 rows
Typical specific speed ranges for hydro-power turbines
Turbine Type
Ns Range
Francis70 – 500
Kaplan / Propeller100 – 350
Pelton, Turgo, Cross-flow10 – 80

Source: engineeringtoolbox.com

Example Calculation

A pump delivers 1500 U.S. gal/min at 100 ft of head while rotating at 1760 rpm. Specific speed varies depending on the unit system:

UnitsCalculationNs
US gpm, ft(1760)(1500)^½ / (100)^(3/4)*2156
British gpm, ft(1760)(1249)^½ / (100)^(3/4)*1967
m³/h, m(1760)(340)^½ / (30.5)^(3/4)*2500
liter/min, m(1760)(5667)^½ / (30.5)^(3/4)*10209

Note: When comparing pumps from different manufacturers, always verify the unit system used in the documentation. The same pump yields different specific speed numbers depending on units.

References

Source: engineeringtoolbox.com