Specific Speed Pump Fan

Overview

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

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

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

Pressure drop due to friction in a pipe.

Variables

Symbol	Description	Unit
$Re$	Reynolds number	—
$\rho$	Fluid density	kg/m³
$v$	Flow velocity	m/s
$D$	Characteristic dimension	m
$\mu$	Dynamic viscosity	Pa·s
$P$	Pressure	Pa
$f$	Darcy 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):

Unit Conversion Factors

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

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:

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:

Units	Calculation	Ns
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

• Original Source