Centrifugal pump: Introduction, components, multistaging,heads and applications. - Mechanicaltalks

Centrifugal pump: Introduction, components, multistaging,heads and applications.

Definition

A hydraulic pump is a machine which converts mechanical energy into hydraulic or water energy.Hydraulic pumps are generally divided into two types: 

1.) Centrifugal pump
2.) Reciprocating pump

Here we will discuss about centrifugal pump in details.
Centrifugal pump

If the mechanical energy is converted into pressure energy by means of centrifugal force acting on the fluid then the hydraulic machine is known as ‘ centrifugal pump’ .

      Centrifugal pump acts as a reverse of an inward radial flow reaction turbine.

Main components of a centrifugal pump are:

 
1.) ImpellerThe rotating part of a centrifugal pump is known as impeller.It consists of a series of backward curved vanes.The impeller is mounted on a shaft which is connected to shaft of an electric motor.
2.) CasingThe casing of a centrifugal pump is similar to casing of a reaction turbine.It is an air tight passage surrounding the impeller and is designed in such a way that kinetic energy of water discharge at the outlet of impeller is converted into pressure energy before water leaves the casing and enters the delivery pipe.

There are three types of casing; 

a.) Volute casing- It is a spiral structural casing in which area of flow increases gradually.The increase in area of flow decrease the velocity of flow.The decrease in velocity increase the pressure of water flowing through the casing.
b.) Vortex casing- If a circular chamber introduced between the casing and impeller then the casing is called as vortex casing.By introducing the circular chamber the loss of energy due to formation of eddies is reduced.Hence the efficiency of pump is more in vortex casing compare to when only volute casing is provided.
c.) Casing with guide vanes- In this casing the impeller is surrounded by a series of guide blades mounted on a ring which is known as ‘diffuser’.The guide blades are designed in such a way that the water from the impeller enters the guide vane without any shock.
3.) Suction pipe with a foot valve and strainer– A pipe whose one end is connected to the inlet of the pump and other end dips into water in a sump known as ‘suction pipe’. 
A foot valve which is a non return valve or one way valve is fitted at the lower end of the suction pipe.The foot valve opens only when the water flows in upward direction.
A strainer is also fitted at the lower end of the suction pipe to prevent the entrance of mud or unwanted particles.We can see these arrangements in diagram given below in different heads portion.
4.) Delivery pipe- A pipe whose one end is connected to the outlet of the pump and other end delivers the water at a required height is known as ‘delivery pipe’.

Multistaging in centrifugal pump:


If a centrifugal pump consists of two or more impellers then the pump is known as  ‘multistage centrifugal pump’.Here the impeller may be mounted on the same shaft or on different shaft.
Multistaging has two major function in hydraulic pumping system;
a.) To produce a high head
b.) To discharge a large quantity of water
A.) Multistage centrifugal pump for high head– 
To obtain a high head a number of impellers are mounted in a series or on the same shaft.The water from the suction pipe enters the first impeller at inlet and discharge at outlet with increased pressure.The water with increased pressure from the outlet of first impeller is taken to inlet of second impeller with the help of connecting pipe.At the outlet of the second impeller the pressure of water will be more than the pressure of water at outlet of first impeller.
       Hence we can conclude that as many as the number of impellers increases the pressure of outlet will be increased further.
Thus, Total head developed= n×H
           Where, n= number of identical impellers mounted on same shaft.
 H= head developed by each impeller.
Note: Discharge passing through each impeller remains same.
B.) Multistage centrifugal pump for high discharge- 

To obtain high discharge the pump should be connected in parallel.Each of the pump must lift the water from a common sump and discharge the water from a common pipe to the delivery pipe.
Note: Each of the pump works under the same head.
Thus, Total discharge= n×Q
Where n= number of identical pumps arranged in parallel.
Q= Discharge from each pump.

Different heads in centrifugal pump


* Suction head- It is the vertical height of the centre line of the centrifugal pump above the water surface in the sump or tank from which water is to be lifted.
It is denoted by Hs.
* Delivery head- The vertical distance or height between the centre line of pump and the water surface at tank to which water is delivered known as delivery head.
It is denoted by Hd.
* Static head- It is defined as the sum of suction head and delivery head.
It is denoted by H.
Thus, H= HS+ Hd

Applications of centrifugal pump

Centrifugal pumps are widely used across every field because of it’s fluid flowing quality.From supplying water to a household to the increasing of pressure of water in a industrial plant,it is that worthy that can use easily.
1.) Centrifugal pumps are widely used in waste water management system, irrigation system, drainage system,food preservation and many other manufacturing processes.
2.) It also finds application in various industries, chemical plants, aerospace for the utilisation of refrigerants.
3.) Centrifugal pumps are also used in powder metallurgy,oil refineries for pumping crude oil.
4.) It has major application in boiler feed water system,air conditioning, heating and ventilation.
5.) It is also used in pharmaceutical industry for medicine treatment.
6.) It is also used in mining application.

That was all about the centrifugal pump. Its introduction, components, multistaging, heads and applications. Hope you all like this article. If this was helpful to you then share this article with your well wishers. If you have any doubts regarding this or any mechanical engineering topics then let us know in comment section or contact us through email. 
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