Water wheel changes the energy of falling water into mechanical energy that can be used for running machinery. The best source of water power in nature is found in waterfalls and rapids in rivers. The water is directed into the wheel through a chute. The wheel is mounted on an axle, which is connected by belts or gearing with the machinery it is to operate.
There are two main types of water wheels, vertical and horizontal. The vertical wheels include the overshot and the undershot.
The overshot water wheel has many scooplike buckets around its edge. Water is delivered to the top of the wheel. The weight of the water falling into the buckets causes the wheel to turn. An overshot water wheel may have an efficiency of up to 80 per cent. That is, it may turn as much as 80 per cent of the energy of the water fed to it into mechanical energy. However, its use is limited to generating small amounts of power.
The undershot water wheel is built so the water strikes against blades at the bottom of the wheel. The power of the wheel depends on the speed of the water as it strikes the blades. The undershot wheel has such a low efficiency that it is rarely used.
Most modern water wheels are horizontal. A horizontal wheel rotates on a vertical shaft. It is driven by the force of the water striking the blades on one side of the wheel. Horizontal wheels are highly efficient if properly designed for the conditions of their use.
Historians believe the water wheel was developed in the 100’s B.C. It was used mainly to grind grain. Later it was used for many kinds of mechanical operations. It was a major source of power until the development of the steam engine in the 1700’s.
