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Water wheels

One of the EngQuest projects is to work as part of a team to construct a water wheel. The 'wheel and axle' part of a water wheel is an example of a simple machine.

If you haven't already done so, why not check out the information on 'wheels and axles' in Simple machines under 'Facts & Articles' (top menu). There you will also find a link to the 'Simple Machines Animation' where you will see a fun example of a water wheel in motion.

Below is some interesting background information about water wheels taken from the 'Construct a water wheel' project on the EngQuest website: www.engquest.org.au

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A Water Wheel is a machine that uses the energy of flowing or falling water (or both) to turn the wheel. The axle of the turning wheel can then power other machines to do work. This kind of power is called hydropower.

Historians are not sure when water wheels were first used, but it is known that they were in use in ancient Greece several centuries BC (Before Christ). They were also widely used in the Roman Empire, including for the pumping of water from mines. It is also thought that water wheels were developed separately in ancient China, where they are known from the first century AD.

Water wheels were used throughout Europe during the Middle Ages, where they were the main source of power for driving large machines. (Other sources of power were windmills and, animal and human power). Water wheels drove the mills that ground grain into flour, and were also used in metal foundries and to drive air blowers for the smelting of iron, for the crushing of rock, and for the hammering of flax leaves to make paper.

The use of water wheels was limited to sites where there were suitable water supplies and slopes. This was not always where the power was needed, such as in the population centres or the mines and quarries. The use of water wheels to power large machines was replaced during the Industrial Revolution by the new technology of steam power, which did not have the same limitations.

The water wheel principle has been revived in more recent times as water-powered turbines that use the energy of water flowing down a slope to generate hydroelectricity.

Water wheels consist of large wooden or metal wheels which have paddles or buckets arranged around the outside rim. The force or the weight of the water on the paddles or buckets turns the wheel.

The axle of the wheel also turns, and this is used to drive the machine by way of belts or gears. The flowing channel of water is called a 'mill race'. The race that brings the water from the 'mill pond' to the wheel is called the 'head race' and the channel that carries the water away is the 'tail race'.

Both horizontal and vertical water wheels have been used, with the vertical type much more common and efficient. Of these, two common designs are the 'undershot water wheel' and the 'overshot water wheel'.

An undershot wheel is mounted above the mill race with the bottom of the wheel in the water. The flowing water strikes the paddles or blades and turns the wheel. The faster the water is flowing the faster the wheel will turn.

In an overshot water wheel the mill race brings the water to the top of the wheel, where it strikes the paddles or buckets and turns the wheel. This is more efficient because as well as the force of the flowing water, the weight of the falling water also helps to turn the wheel. This design sometimes had buckets mounted only on one rim of the wheel, so that these filled with water, making that side of the wheel heavier.

Because it uses the potential energy of the falling water, an overshot water wheel will still work even when the flow of water is not very fast. The larger the diameter of the wheel, the greater 'leverage' and so the greater turning effect on the axle that drives the machine.

The Beaconsfield Gold and Heritage Museum (Grubb Shaft) in Tasmania has a working overshot water wheel that drives a huge stamping-battery machine that was used to crush the quartz ore containing gold. The machine was built in 1862 and still works!

Another fine Australian example is the Bridgewater Mill in South Australia built by John Dunn in 1859 as a flour mill, and still preserved. This Water Wheel is an example of a 'backshot wheel', a version of the overshot water wheel where the water from the race is introduced just behind the top of the wheel.