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Reciprocating Pump (Single-acting and Double-acting reciprocating pump)

Reciprocating pump:- If the mechanical energy is converted into hydraulic energy by sucking the liquid into a cylinder in which a piston is reciprocating, which exerts the thrust on the liquid and increases its hydraulic energy is know as reciprocating pump.A reciprocating pump is a positive plunger pump. It is often used where relatively small quantity of liquid is to be handled and where delivery pressure is quite large. Reciprocating pump consists of following parts.
1. A cylinder with a piston             5. suction pipe
2. piston rod                                    6. delivery pipe
3. connecting rod                           7. suction valve
4. crank                                            8. delivery valve

Working of a single-acting reciprocating pump

single-acting reciprocating pump
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Single acting reciprocating pump:-
A single acting reciprocating pump, which consists of a piston which moves forwards and backwards in a close fitting cylinder. The movement of the piston is obtained by connecting the piston rod to crank by means of a connecting rod. The crank is rotated by means of an electric motor. Suction and delivery pipes with suction valve and delivery valve are connected to the cylinder. The suction and delivery valves are one way valves or non-return valves, which allow the water to flow in one direction only. Suction valve allows water from suction pipe to the cylinder which delivery valve allows water from cylinder to delivery pipe.
The rotation of the crank brings about an outward and inward movement of the piston ‘P’ in the cylinder ‘C’. During the suction stroke the piston is moving towards right in the cylinder, this movement of piston causes vacuum in the cylinder. The pressure of the atmosphere acting on the sump water surface forces the water up in the suction pipe ‘S’. The forced water opens the suction valve V1 and the water enters the cylinder.The piston from its extreme right position starts moving towards left in the cylinder.The movement of the piston towards left increases the pressure of the liquid inside the cylinder more than atmospheric pressure. Hence suction valve closes and delivery valve V2 opens. The liquid is forced into the delivery pipe and is raised to a required height.
For one revolution of the crank, the quantity of water raised up in the delivery pipe is equal to the stroke volume in the cylinder in the single acting pump and twice this volume in the double acting pump.

Discharge through a single acting reciprocating pump.

    D = diameter of the cylinder
    A = cross section are of the piston or cylinder
    r = radius of crank
    N = r.p.m of the crank
    L = Length of the stroke = 2 r
    hs =  Suction head or height of the axis of the cylinder from water surface in sump.
    hd =  Delivery head or height of the delivery outlet above the cylinder axis.
Discharge of water in one revolution = Area x Length of stroke
                                     = A L
Number of revolution per second =  N/60
Discharge of the pump per second
 
            Q = Discharge in one revolution No.of revolution per second
         
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Working of a Double-acting reciprocating pump.

double acting reciprocating pump
Double acting reciprocating pump:- In a Double-acting reciprocating pump, each stroke of the piston carries out both the functions, suction as well as delivery. Thus it require two suctions pipes and two delivery pipes for double-acting pump. When there is a suction stroke on one side of the piston, there is at the same time a delivery stroke on the other side of the piston. Thus for one complete revolution of the crank there are two delivery strokes and water is delivered to the pipes by the pump during these two delivery strokes.

Discharge through a double-acting reciprocating pump.

D1= delivery valve(closed)
D2= delivery valve(being opened)
S1= suction valve (being opened)

S2= Suction valve (closed)

Discharge double acting reciprocating pump
The above equation gives the discharge of a double-acting reciprocating pump. This discharge is two times the discharge of a single-acting pump.

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