Describe the construction and mode of operation of a lift pump

Construction:
A lift pump consists of a cylinder with a piston that moves up and down. The piston has a valve (piston valve) that opens upwards. At the bottom of the cylinder, there is another valve (foot valve or suction valve) that also opens upwards. A suction pipe connects the foot valve to the water source, and a delivery spout is located near the top of the cylinder.

Mode of Operation:

1. Upstroke: When the piston is pulled upwards, the volume of air below it increases, causing the pressure to drop. The higher atmospheric pressure on the water surface in the well pushes water up the suction pipe, opening the foot valve. Water fills the cylinder below the piston. The piston valve remains closed.
2. Downstroke: When the piston is pushed downwards, the water below it is compressed. This increased pressure closes the foot valve and forces open the piston valve. Water flows through the piston valve to the top side of the piston.
3. Subsequent Upstroke: As the piston is pulled upwards again, the water above the piston is lifted and discharged through the delivery spout. Simultaneously, the pressure below the piston drops again, opening the foot valve and drawing more water into the cylinder from the well. This cycle repeats, continuously lifting water.