A water or lift pump, often called a tube well, is used to lift water from a lower level to a higher level. These pumps are used in houses or on roads for boosting up the underground water. They work on the principle that atmospheric pressure can support a vertical column of water upto 9 metres in height.
In this pump, an iron pipe is put into the ground up to the level of water. On the top of this pipe, another pipe of bigger diameter is fitted. Several components of the pump are fitted into this pipe. It consists of a handle which is connected to a piston which moves up and down, inside the barrel. It contains two valves, of which one is fitted with the piston and the other at the junction of the two pipes. Both these valves open only in the upward direction.
When the piston is pulled up with the help of the handle, the pressure in the iron pipe falls. This opens the valve fitted at the junction of the two pipes closing the upper valve. During this action, the pressure above the surface of water becomes less than the atmospheric pressure. This makes the water rise up in the pipe.
Similarly when the handle is pulled up, the piston goes down and the valve at the joint closes due to the weight of water. Now the compression of water opens the upper valve. This makes the water rise up further. With this repeated action the water level continues to rise until water comes out at the top.
However, this pump has two limitations. Firstly, water is discharged only on the upward stroke. And, secondly, although in principle, it can lift water upto a height of 9 metres, in practice it is only about 8 metres (or 30 ft) above the water surface.
The modified version of this pump is called force pump. In this pump, the upper valve is not fitted to the piston but to the opening. With this modification, the water can be pumped to a much higher height. Force pump can raise water from greater depths and is used to send water to the upper floors of multi-storeyed buildings. For the continuous supply, centrifugal pumps are used these days. These usually run on petrol, diesel or electricity.
