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What is the function of volute casing in centrifugal pump?

 Function of volute casing in centrifugal pump?

Functions of a pump volute:

  • To convert kinetic energy impaired by the impeller into pressure energy
  • To minimize losses during this energy conversion process
  • The pump casing does not take any part in dynamic head generation
  • The best volutes are of constant velocity design
  • Kinetic energy is converted into pressure energy only in the diffusion nozzle immediately after the volute throat

Various types of volute

  1. Single volute
  2. Double volute
  3. Vertical pump with diffuser
  4. Volute with diffuser vanes
  5. Circular volute
Double Volute

  • A double volute casing has two single volutes 180° apart
  • Total throat area of two volute is same as the throat area of a comparable single volute
  • Double volute significantly reduces the radial load problem of the single volute pump
  • Hydraulic performance of a double volute pump is nearly the same as that of a single volute
  • Double volute pump is around 1-1.5 point less efficient at B.E.P but about two points more efficient on either side of B.E.P.
  • Double volutes are not used for flows below 90 m3/hr (400 US GPM)

Vertical Pump with Diffuser

  • A vertical pump consisting of a series or a set of stationary vanes surrounding the impeller
  • Diffuser directs the flow and allows a more gradual expansion thereby increasing the efficiency of the centrifugal pump

Volute with Diffuser Vanes

Diffuser vanes are stationary vanes, fitted in the pump casing or diffuser. They convert velocity into pressure energy and guide the fluid to the impeller vanes of the subsequent stage.
Functions of the diffuser vanes
  • Direct the flow
  • Allow a more gradual expansion
Multistage Pump
It efficiently reduces the velocity and in the case of a Diffuser multistage pump, directs this lower velocity fluid into vaned return channels which guide the liquid to the inlet or eye of  the next stage impeller.

Single Stage Pump
In the case of a single stage pump, the discharge fluid from the diffuser is collected in a surrounding casing, which guides the liquid out of the pump through the discharge nozzle.

Circular Volute

  • It is concentric with respect to the impeller 's longitudinal axis.
  • A circular chamber is provided between the casing and the impeller.
  • Flow paths in a circular volute are often split as flow takes the path of least resistance to the stage exit.


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