If a reciprocating pump uses one side of the piston for pumping liquid, then it is known as a Single Acting Reciprocating Pump.
The main parts of a single acting reciprocating pump are discussed below.
1.Cylinder, Piston, Piston Rod, Connecting Rod and Crank
A single action reciprocating pump consists of a piston, which moves forwards and backwards inside a close fitting cylinder. The movement of the piston is obtained by connecting the piston rod to the crank by means of a connecting rod. The crank is rotated by an electric motor.
2.Suction Pipe and Suction Valve
Suction pipe is connected to the cylinder. Suction valve is a one way valve, i.e., non-return valve. It allows the liquid to flow in one direction only. That is, it permits the liquid from the suction pipe to the cylinder.
3.Delivery Pipe and Delivery Valve
Delivery pipe is connected to the cylinder. Delivery valve is also one non-return valve. It permits the liquid to flow in one direction only. That is, it allows the liquid from the cylinder to the delivery pipe.
In a single-action reciprocating pump, liquid acts on one side of the piston only. A single-acting reciprocating pump which has one suction pipe and one delivery pipe; It is usually placed above the liquid level in the sump.
When the crank rotates from IDC to ODC the piston moves towards right in the cylinder. This is called suction stroke.
Now, the volume covered by the piston within the cylinder increases. On the free surface of water in the sump, atmospheric pressure acts. Thus there is a pressure different at the two ends of the suction pipe which connects the sump and the cylinder. This pressure difference between the free surface and inside of the cylinder causes the flow of water from the sump into the cylinder through the suction valve, which is kept open.
During this stroke, the non-return valve at the delivery side will be closed by the atmospheric pressure existing in the delivery pipe. At the end of this stroke, the cylinder will be full of water, the piston reaches the right end, which is called outer dead centre since, the water is continuously sucked into the cylinder, this stroke is called suction stroke. At the end of this stroke, since the pressure in the cylinder is atmospheric, the suction valve is closed.
2.Return stroke or Delivery Stroke
When the crank rotates the piston from its extreme right position starts moving towards left in the cylinder. This is known as Return or Delivery Stroke.
The movement of piston towards left increases the pressure of the liquid inside the cylinder to a pressure more than atmospheric pressure. Therefore, the Suction valve closes the delivery valve opens. The liquid inside the cylinder is forced into the delivery pipe through the delivery valve. Consequently, the liquid is raised to the required height. The liquid is discharged at every alternate stroke.