A hand pump works on the principle of displacement applied through the use of a piston and sucker rods that help to lift water out from the bottom. Water displacement occurs when pressure is applied on the piston and sucker rods manually using the handle of the pump.
The hand pump comprises of a series of sucker rods present inside drop pipes. These rods act as the mechanical connection between the handle and piston of the pump.
When the handle or the lever arm of the hand pump is lifted upwards, it causes the piston and sucker rods of the pump to be pushed down. Simultaneously, the lower ball valve of the piston seals owing to the pressure generated and the seal at the upper end lifts. This causes water to flow over the piston.
Next, when the lever arm is pushed down, the piston and rods lift up and the ball valve gets sealed in its position causing the entire quantity of water above the piston to be lifted up. At the same time, more water gushes into the cylinder from the bottom, ready to be lifted the next time the pump handle is pushed up.
Owing to its principle of working, the hand pump is called the positive displacement lift pump.