Centrifugal Pump parts and its basic function

The major parts of centrifugal pump are:

Impeller

Impeller nut

Seal

Casing

Wear rings

Shaft

Shaft sleeve

Coupling

Bearings

Stuffing box

Back plate

Bearing Housing 

Gland

Impeller

The impeller is a vaned disk mounted on the shaft. Its function is to increase the pressure of the liquid by means of its rotating action. The impeller is the main rotating part that provides the centrifugal acceleration to the fluid. 

Impeller nut

Function of Impeller nut is:

To lock the impeller in its proper axial position

To prevent axial movement due to hydraulic thrust

Seal

A pump may be provided with one of two types of sealing elements - packing rings or mechanical seal. The sealing elements prevent the leakage of the pumped liquid into the atmosphere.

Casing

Casings are generally of two types: volute and circular. The impellers are fitted inside the casings. The casing contains the liquid and acts as a pressure containment vessel that directs the flow of liquid in and out of the pump. 

Volute casings build a higher head; circular casings are used for low head and high capacity. A volute is a curved funnel increasing in area to the discharge port.
Circular casing have stationary diffusion vanes surrounding the impeller periphery that convert velocity energy to pressure energy. Conventionally, the diffusers are applied to multistage pumps.

Wear rings

Wear ring provides an easily and economically renewable leakage joint between the impeller and the casing. 

Casing wear rings on larger pumps are sometimes held in place with a flange screwed to the casing. In axial pumps, the casing wear rings are just set on a pin.

Impeller wear rings are often press fit or shrink fit onto the impellers. Set screws are used with these fits at times to provide added strength to the fit.

Shaft

The basic function of a centrifugal pump shaft is to transmit the torques encountered when starting and during operation while supporting the impeller and other rotating parts.

Shaft Sleeve

Function of shaft sleeve is:

-To protect the shaft from erosion & corrosion

-To enhance the stiffness of the rotating element

-To protect the shaft from abrasion wear at packed stuffing box or at leakage joints

Coupling

The function of a coupling is to connect the pump shaft and the driver shaft, and to transmit the input power from the driver into the pump.

Shaft couplings can be classified in to two groups:

1) Rigid couplings- These couplings are used in applications where there is absolutely no possibility or room for any misalignment.

2) Flexible couplings- These couplings are more prone to selection, installation and maintenance errors. Flexible shaft coupling can be divided in to two groups: elastomeric and non-elastomeric. 

Bearings

The functions of the bearings are to support the weight of the shaft (rotor) assembly, to carry the hydraulic loads acting on the shaft, and to keep the pump shaft aligned to the shaft of the driver.

Stuffing Box 

Stuffing box both refer to a chamber, either integral with or separate from the pump case housing that forms the region between the shaft and casing where sealing media are installed. When the sealing is achieved by means of a mechanical seal, the chamber is commonly referred to as a Seal Chamber. When the sealing is achieved by means of packing, the chamber is referred to as a Stuffing Box. Both the seal chamber and the stuffing box have the primary function of protecting the pump against leakage at the point where the shaft passes out through the pump pressure casing. 

Back Plate

The back plate is of pressed steel manufacture, which together with the pump casing forms the actual fluid chamber in which the fluid is transferred by means of the impeller.

Bearing Housing

The bearing housing is used to enclose and protect the shaft bearings, ensuring proper alignment. The housing will also include some type of method for lubricating the bearings and cooling the pump.

Gland 

The gland is a very important part of the seal chamber or the stuffing box. It gives the packing’s or the mechanical seal the desired fit on the shaft sleeve. 

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