Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Efficiency in Pumps or Fans

Sponsored Links

For a fluid flow process involving a pump or fan the overall efficiency is related to the

  • hydraulic
  • mechanical
  • volumetric

losses in the pump or fan.

Hydraulic Loss and Hydraulic Efficiency

Hydraulic losses relates to the construction of the pump or fan and is caused by the friction between the fluid and the walls, the acceleration and retardation of the fluid and the change of the fluid flow direction.

The hydraulic efficiency can be expressed as:

ηh = w / (w + wl)                            (1)


ηh = hydraulic efficiency

w = specific work from the pump or fan (J/kg)

wl = specific work lost due to hydraulic effects (J/kg)

Mechanical Loss and Mechanical Efficiency

Mechanical components - like transmission gear and bearings - creates mechanical losses that reduces the power transferred from the motor shaft to the pump or fan impeller.

The mechanical efficiency can be expressed as:

ηm = (P - Pl) / P                              (2)


ηm = mechanical efficiency

P = power transferred from the motor to the shaft (W)

Pl = power lost in the transmission (W)


Volumetric Loss and Volumetric Efficiency

Due to leakage of fluid between the back surface of the impeller hub plate and the casing, or through other pump components - there is a volumetric loss reducing the pump efficiency.

The volumetric efficiency can be expressed as:

ηv = q / (q + ql)                               (3)


ηv = volumetric efficiency

q = volume flow out of the pump or fan (m3/s)

ql = leakage volume flow (m3/s)

Total Loss and Overall Efficiency

The overall efficiency is the ratio of power actually gained by the fluid to power supplied to the shaft. The overall efficiency can be expressed as:

η = ηhηmηv                               (4)


η = overall efficiency

The losses in a pump or fan converts to heat that is transferred to the fluid and the surroundings. As a rule of thumb - the temperature increase in a fan transporting air is approximately 1oC.

Example - Hydraulic Efficiency for a Pump

An inline water pump works between pressure 1 bar (1 105 N/m2) and 10 bar (10 105 N/m2). The density of water is 1000 kg/m3. The hydraulic efficiency is ηh = 0.91.

The actual water head (water column) can be calculated as:

h = (p2 - p1) /γ

    = (p2 - p1) /ρ g

    = ((10 105 N/m2) - (1 105 N/m2)) / (1,000 kg/m3) (9.81 m/s2)

    = 91.7 m - water column

The pump must be constructed for the specific work:

wc = g h /ηh

    = (9.81 m/s2) (91.7 m) / 0.91

    = 988.6 (J/kg, m2/s2)

The construction or design head is:

h =wc / g

    = (988.6 m2/s2) / (9.81 m/s2)

    = 100.8 m - water column

Sponsored Links

Related Topics


Design of pumping systems and pipelines. With centrifugal pumps, displacement pumps, cavitation, fluid viscosity, head and pressure, power consumption and more.

Related Documents

Centrifugal Pumps - Influence of Viscosity

Hydrodynamic losses through pumps depends on fluid viscosities.


The measure of usefulness.

Power Gained by Fluid from Pump or Fan

Calculate the power gained by fluid from an operating pump or fan.

Pump Power Calculator

Calculate pumps hydraulic and shaft power.

Pumping Water - Required Horsepower

Horsepower required to pump water.

Pumps - Specific Speed

Characterizing of impeller types in pumps in a unique and coherent manner.

Pumps - Suction Specific Speed

Suction Specific Speed can be used to determine stable and reliable operations for pumps with max efficiency without cavitation.

Static Pressure vs. Head

Static pressure vs. pressure head in fluids.

System Curve and Pump Performance Curve

Utilize the system curve and the pump performance curve to select the proper pump for a particular application.

Turbo Machines - Specific Work done by Pumps, Compressors or Fans

Calculate specific work done by pumps, fans, compressors or turbines.

Sponsored Links

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

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


We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.