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Sunday, 15 September 2019

WORKING PRINCIPLE OF RECIPROCATING PUMP

We were discussing a new topic i.e. reciprocating pump in our recent post and we have seen there the basics of a pump and main components of a reciprocating pump.  

Today we will start here with the working principle of reciprocating pump and we will also find out here the discharge through a reciprocating pump and work done by reciprocating pump with the help of this post. 

Working principle of reciprocating pump 

If the mechanical energy is converted in to stored mechanical energy or pressure energy by sucking the liquid in to a cylinder in which a piston is reciprocating backward and forward, which exerts the thrust on the liquid and increases its hydraulic energy or pressure energy, the hydraulic machine will be termed as reciprocating pump. 

There are following main components of a reciprocating pump mentioned here. Following figure displayed here indicates the reciprocating pump. 
  1. A cylinder with a piston, piston rod, connecting rod, crank and crank shaft 
  2. Suction pipe 
  3. Delivery pipe 
  4. Suction valve 
  5. Delivery Valve 

Above figure indicates the single acting reciprocating pump. Piston will move within a cylinder in forward and backward direction towards inner dead center and outer dead center i.e. piston will execute the reciprocating motion within the tight fit cylinder. 

Reciprocating movement of piston within tight fit cylinder will be executed by connecting the piston with crank with the help of connecting rod as displayed in figure. Crank will be fixed with crank shaft which will be rotated by an electric motor. 

Suction pipe and delivery pipe will be fixed with the cylinder by means of suction valve and delivery valve respectively as displayed in above figure. 

Suction valve and delivery valve will be check valve i.e. non return valve and hence water may flow in one direction only through these valves. 

Let us see how a reciprocating pump works 

When piston will move towards right i.e. towards outer dead center, there will be fall in pressure of liquid and hence due to reduction in pressure suction valve will be opened and liquid will enter in to the cylinder. This movement of piston inside the cylinder will be termed as suction stroke. 

When piston will move towards left i.e. towards inner dead center, there will be increase in pressure of liquid and hence due to increase in pressure of liquid suction valve will be closed and delivery valve will be opened and liquid under high pressure will flow through the delivery valve to delivery pipe of reciprocating pump. 

Discharge through a reciprocating pump 

Let us consider the following terms as mentioned here for a reciprocating pump displayed above in figure. 

D = Diameter of the cylinder 
A = Cross sectional area of the piston or cylinder 
r = Radius of crank 
N = R.P.M of crank 
L = Length of the stroke = 2 x r 
hs = Suction head or Height of the cylinder axis from the water surface in the sump 
hd = Discharge head or height of delivery point from the cylinder axis 

Volume of water delivered in one revolution = Area x Length of stroke 
Volume of water delivered in one revolution = A x L 
Number of revolution per second = N/60 
Volume of water delivered per second = Volume of water delivered in one revolution x Number of revolution per second 
Volume of water delivered per second = A x L x N/60 
Volume of water delivered per second = A L N/60 

Discharge of the pump per second = A L N/60 


Work done by reciprocating pump

Work done by reciprocating pump will be given by following equation as mentioned here

Work done by reciprocating pump = Weight of water lifted per second x Total water through which water is lifted 

Work done by reciprocating pump = ρ x g x Discharge of the pump per second x Total water through which water is lifted 

Work done by reciprocating pump = ρ g A L N x (hs + hd) / 60 


So, we have seen here the working principle of reciprocating pump. We have also secured here the expressions for discharge through a reciprocating pump and work done by reciprocating pump with the help of this post.  

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Further we will find out, in our next post, ideal indicator diagram of reciprocating pump.  

Reference: 

Fluid mechanics, By R. K. Bansal 

Image courtesy: Google  

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