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Monday, 23 September 2019

DOUBLE ACTING RECIPROCATING PUMP: WORKING PRINCIPLE, DISCHARGE, WORK DONE AND POWER REQUIRED

We were discussing the basics of reciprocating pumpmain components of a reciprocating pumpworking principle of reciprocating pumpideal indicator diagram of reciprocating pump, effect of acceleration and friction on indicator diagram of reciprocating pump and expression for acceleration head in the suction pipe of a reciprocating pump in our recent posts.  

Today we will see here the basics of double acting reciprocating pump: working principle, discharge, work done and power required with the help of this post. 

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. 

We were discussing earlier reciprocating pump with single piston and single acting, where we have discussed in detail how water is being sucked through suction pipe during suction stroke and how water is being discharged through delivery pipe during delivery stroke. 

In case of single acting reciprocating pump. there will be only one stroke in first half of revolution of crank and second stroke will be done during second half crank revolution. Hence, in case of single acting reciprocating pump, there will be one suction stroke and one delivery stroke for one complete revolution of crank. 

Now we will be interested here to understand the working principle of double acting reciprocating pump. We will also find out here the work done, discharge and power required for a double acting reciprocating pump. 

Double acting reciprocating pump: Working principle, Discharge, work done and power required 

Water will be acting on both side of the piston in case of double acting reciprocating pump as displayed here in following figure. Therefore, there will be two suction and two delivery pipes for double acting reciprocating pump as shown in following figure. 

When there will be a suction stroke on one side of the piston, same time there will be a delivery stroke at the other side of the piston. 

Hence, in case of double acting reciprocating pump, there will be two suction strokes and two delivery strokes for one complete revolution of crank and water will be discharged through the delivery pipes during these two delivery strokes. 

Let us consider the following terms as mentioned below
D = Diameter of the piston
d = Diameter of the piston rod 

Area on one side of the piston, A = (π/4) x D2
Area on other side of the piston where piston rod is connected with piston, A1 = (π/4) x [D2 -d2

Discharge of the double acting reciprocating pump

Volume of water delivered in one revolution of the crank will be determined as mentioned below

V = A x Length of stroke + A1 x Length of stroke

Discharge of pump in one revolution of the crank will be determined as mentioned below

Discharge of pump = Volume of water delivered in one revolution X No. of revolution in one second 


If diameter of the piston rod i.e. d is very small as compared to the diameter of the piston i.e. D, then we can neglect it and discharge of the pump could be written as mentioned below. 


Above equation is the equation for the discharge of the double acting reciprocating pump. We can say that, discharge of the double acting reciprocating pump will be double of the discharge of the single acting reciprocating pump. 


Work done by double acting reciprocating pump 

Work done per second = Weight of water delivered x total height


Power required to drive the double acting reciprocating pump 

Power required to drive the pump will be given by following equation as mentioned below 

So, we have seen here the basics of double acting reciprocating pump and expression for the discharge, work done and power required to drive the double acting reciprocating pump here.  

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Further we will find out, in our next post, slip and negative slip in reciprocating pump.  

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google  

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