Introduction to Water Wheels
Introduction To Water Wheels
Find out more about using the power of a waterwheel
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Water wheel (or
Waterwheel) is a system for extracting usable power from the water flowing in a river or stream. Along with windmills, water wheels have being powering the milling of flour and other industry for hundreds of years. Waterwheels are still in common use in Nepal (25,000+), and India (over 200,000 waterwheels).
Water wheels come in two main flavours:
undershot, and
overshot. Historically the undershot water wheel was the commonest as it is the cheaper and simpler to build. It was used frequently by the Romans and the undershot water wheel is sometimes known as a
Vitruvian water wheel after the Roman engineer Vitruvius. In this system the wheel is placed over a fast flowing river. The water hits paddles which protrude all around the wheel and therefore turns the wheel. This system can only be used where the flow of water is very fast as little of the energy of the water (around 20%) is used.
The Overshot water wheel is more complicated, but much more efficient as almost all of the water flow is used for power. A dam and a pond or lake are built and used to channel water to just below the top of the wheel where it collects in buckets. The weight of the water in the buckets turns the wheel as the buckets on the otherside are empty and therefore lighter. When a filled bucket has caused the wheel to rotate, and that bucket has reached the bottom of the wheel, it is inverted and the
tail water falls out. That bucket the continues around the wheel empty until it gets back up to the top to be filled again. Around 70% of the energy carried by the water is used in an overshot waterwheel.
Other alternatives are the
breasthot waterwheel in which the water arrives at the wheel at axle height (rather than at the top in the case of an overshot), or most efficient of all, the
pitchback waterwheel in which the water does not flow over the top of the wheel, but actually flows into the wheel and turns the wheel in the opposite direction. It's difficult to explain in words, so here are a couple of useful diagrams:
Historically waterwheels were used to turn milling stones and other mechanical tasks. However they are not being reconsidered for the
generation of electricity. A waterwheel for example has a lot less environmental impact than hyroelectric power generation since rivers do not need to be diverted, and the pressure of the water is not increased and so fish are less likely to be injured or killed. The costs per Watt of power is just £3 to £7.50 (according to
Southampton University) which is comparable to the costs of photovoltaic cells. Waterwheels are excellent where there is a large volume of flowing water with
low head (i.e. the height difference between the water at the waterwheel, and the water for example 1km away is not small).
Article Last Modified: 22:11, 11th Apr 2006
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