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.
- A cylinder with a piston, piston rod, connecting rod, crank and crank shaft
- Suction pipe
- Delivery pipe
- Suction valve
- 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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Reference:
Fluid mechanics, By R. K. Bansal
Image courtesy: Google
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