Pumps are the machines capable of converting mechanical energy into hydraulic energy (pressure energy). In reciprocating pumps liquid is sucked in a cylinder in which piston is reciprocating. This action of piston exerts thrust on liquid and increases its hydraulic energy. Such type of pumps are called as reciprocating pumps.

Construction of reciprocating pumps - Single acting

The main components of such a pump are:-

1) Suction pipe and valve
2) Cylinder - piston arrangement with connecting rod and crank
3) Delivery pipe and valve


As shown in the figure crank is connected to connecting rod, through which piston (closely fitted to cylinder) is connected. The crank is rotated by the means of electric motor. When crank rotates, connecting rod provides reciprocating action to the piston. 

Suction pipe and delivery pipe with their valves are connected to cylinder. The valve is provided so that only one way motion is possible and fluid does not return to sump. The suction pipe allows entry of liquid from sump to the cylinder only and Similarly delivery valve allows liquid flow from cylinder to delivery pipe only.


When motor is powered, it rotates the crank which allows the piston to reciprocate (to and fro motion) in the cylinder. Initially suppose the piston is in extreme left end. On rotation of crank, it starts moving right. Due to this partial vacuum in the cylinder is created. But the surface of the liquid in sump is experiencing atmospheric pressure which is greater than that inside the cylinder. Thus liquid is forced to move in suction pipe and enters the cylinder by passing through suction valve. When piston starts moving from extreme right end to leftwards, then pressure on the liquid is higher then atmospheric pressure. This closes the suction valve and opens delivery valve and liquid is forced out of delivery pipe. Thus weight can be lifted through this pressurized liquid. 

Discharge and Work done by reciprocating pump

Discharge (Q) can be calculated by formula 

                                   Q = A X L X (N/60)

Where A is cross section area of piston or cylinder 

L is length of stroke

N is rpm of crank and (N/60) means revolution per second.


Work done (W) by reciprocating pump per second can be given by equation

                    W = Density x Gravity x LAN/60
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