CENTRIFUGAL PUMPS

 CENTRIFUGAL PUMPS




 Introduction

Pumps are used to move liquid from place to place in a plant. Pumps can increase the pressure, the flow rate or both or both of these at the same time. In order to move liquids, pumps must exert force on the liquid. Pumps may transfer force to the liquid to be moved in three (3) different ways. They are:

         

1.       By pulling the liquid.

2.       By pushing the liquid.

3.       By throwing the liquid.

 

Many pumps use more than one of these at the same time. Pumps may be classified on the basis of the applications they serve. All pumps are classified in to two (2) major categories. They are:

 

1.       Dynamic Pumps.

2.       Positive Displacement Pumps.

 

Dynamic pumps are further divided in to:

 

1.       Centrifugal Pumps

2.       Special effect pumps e.g.: Jet Pumps

 

Positive Displacement Pumps are divided in to Reciprocating and Rotary Pumps. Reciprocating Pumps are further divided into:

 

1.       Piston Pumps  

2.       Plunger Pumps

3.       Diaphragm Pumps

 

Rotary Pumps are further divided in to:

 

1.       Gear Pumps

2.       Vane Pumps

3.       Screw Pumps

 

In Dynamic Pump, the energy is continuously added to increase the fluid velocities within the machine to values in excess of those occurring at the discharge such that subsequent velocity reduction within or beyond the pump produces a pressure increase.

 

In a Displacement Pump, energy is periodically added by application of force to one or more movable boundaries of any desired number of enclosed, fluid- continuing volumes, resulting in a direct increase in pressure up to the value  required to move the fluid through the valves or ports in to the discharge line.

 

Centrifugal Pumps move liquid by catching the liquid in a spinning wheel and "throwing" it out from the center. This movement is a result of centrifugal force on the liquid.

 

Centrifugal Pumps


A centrifugal pump consists of a set of rotating vanes enclosed within a housing or casing and used to impart energy to a fluid through centrifugal force. A Centrifugal Pump has two main parts:

 

          1.       A rotating element including an impeller and a shaft.

          2.       A stationary element made up of casing, stuffing box and bearings.

 

In a centrifugal pump the liquid is forced by atmospheric or by other pressure in to a set of rotating vanes. These vanes constitute an impeller which discharges the liquid at its periphery at a higher velocity. This velocity is converted to pressure energy by means of a volute or by a set of stationary diffusion vanes surrounding the impeller periphery.


Types  of  Centrifugal  Pumps

Centrifugal  pumps  are  further  divided  into  two  main  categories:

 

1)   Single  stage

2)   Multi-stage

 


Centrifugal Pumps - Parts




Driver

A  driver  is  the  section  which  provides  energy  for  spinning  the  impeller  in  the  pump.  Normally  the  drivers can be electric  motor, steam turbines, gas turbines and diesel engines.

 

Shaft

A  pump  is  connected  to  an  electric  motor  by  means  of  a  shaft.  A  shaft  is  a  steel  solid  cylindrical  part  generally  used  for  transmitting  rotary  motion  from  one  machine  to  another.

 

In  a  pump  assembly,  there  are  two  shafts. Pump  and  Motor  Shaft.  These  shafts  are  connected  to  each  other  by  device  which  is  called  coupling.

 

Coupling

A  coupling  is  used  to  connect  driver with driven machinery.  The  main  purpose  of  a coupling  is  to  transmit  rotary  motion  from  one  piece  of  equipment  to  another.   Coupling  may  perform  other  secondary  functions,  such  as  accommodating   misalignment  between  the  two  shafts,  to  some  extent  acting  as  a  buffer  for  harmful  vibration  of  the  driver.

 

Impeller




The  most important part  of  a  Centrifugal  Pump  is the impeller. The impeller is like a wheel. It is inside the casing.  The  impeller  is  connected  to  a  shaft. The shaft goes through the casing and is connected to the pump driver. When the drive is started, the shaft spins the impeller.

Mechanical Seal



 Mechanical seals are critical components in centrifugal pump systems. These devices preserve the integrity of the pump systems by preventing fluid leaks and keeping contaminants out. Mechanical seal systems are used on various seal designs to detect leakage, control the seal environment and lubricate secondary seals


 


 

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