AODD Configurator

AODD Configurator

Centrifugal pump: how it works

4 December 2018

In a centrifugal pump the movement of the fluid is provided by rotating mechanical parts (commonly referred to as impellers).
It uses the centrifugal effect of the impeller to move the fluid, transforming the mechanical energy (from a motor, that in most cases is electric), into kinetic energy and then into pressure.


The main components of a centrifugal pump are:

  • Mobile part, called the impeller, that transfers the energy
  • Pump casing, the volute that channels the flow, firstly in suction and then in delivery
  • Shaft on which the impeller is secured and connected to the motor
    Motor, that can be electric or internal combustion

There are obviously different types of centrifugal pumps, such as the magnetic drive type, where the movement is transferred to the impeller with the magnetic force and not by a rotating shaft.


The main types of impeller are:

  • Open, usually used when the fluid is dirty
  • Closed, when a greater efficiency is required at the expense of versatility

The movement of the impeller creates a vacuum in the suction pipe and the fluid, pushed by the atmospheric pressure, flows into the pipe and enters the pump.

The impeller, after having sucked the fluid, sends it towards the sides of the pump casing, through the centrifugal force produced by its rotating speed.

The impeller is fitted with a series of curved paddles that form channels with an increasing cross section, from the centre outwards.
The fluid exits the impeller at the speed Vt, therefore still with kinetic energy and enters the volute.
The pump casing, or volute, is also built with an increasing section, so that the remaining amount of kinetic energy is transformed in pressure, thus increasing the head.


Example: Debem MB140 centrifugal pump.

The pump characteristics are described by the curve that shows the progress of the head provided by the pump in relation to the flow rate that it supplies.

These vary based on the size of the impeller.

In practice the curves of the NPSH (Net Positive Suction Head) and of the absorbed power are supplied, with a view to the flow rate and sometimes also the performance.


Based on the position of the shaft and the motor there are:

  • Horizontal pumps, usually positioned outside the cisterns
  • Vertical pumps, partially immersed in the liquid

The horizontal pumps can also be divided into:

  • Pumps above head, where the distance between the pump and the surface of the fluid in suction is positive, with a risk of cavitation.
  • Pumps below head, where the distance between the pump and the surface of the fluid in suction is negative, where cavitation is much rarer.
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