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in Rome, Georgia ]] A water wheel (also '''waterwheel''', '''Norse mill''', '''Persian wheel''' or '''noria''') is a Hydropower system; a system for extracting power from a flow of water. It was a widely used system in the Middle Ages , powering most industry in Europe , along with the Windmill . The most common use of the water wheel was to mill flour, where it was known as the Watermill , but other uses included foundry work and machining, and pounding Linen for use in Paper . The largest waterwheels in the world are located in the Syria n city of Hama . A water wheel consists of a large wheel, typically Wood en, with a number of Blade s or Bucket s arranged on the outside rim forming the driving surface. The wheel is mounted vertically on a horizontal Axle that is used as a power take-off. Historic water wheels came in two basic forms – undershot and '''overshot'''. OVERSHOT WHEEL The overshot wheel has the water channeled to the wheel at the top and slightly to one side in the direction of rotation. The water collects in the buckets on that side of the wheel, making it heavier than the other "empty" side. The weight turns the wheel, and the water flows out into the tail-water when the wheel rotates enough to invert the buckets. The overshot design uses almost all of the water flow for power (unless there is a leak) and does not require rapid flow. The overshot wheel is a far more powerful and efficient design, but because it requires constructing a dam and a pond it is far more capital intensive. and norias (water wheels) in Hama ]] UNDERSHOT WHEEL The undershot design, sometimes called 'Vitruvian' after the Roman engineer Vitruvius , places the wheel over a fast-flowing body of water. Here it is the flow of the water directly against the buckets (or paddles) that turns the wheel, not the weight. It has the advantage of being cheaper and simpler to build, but is less powerful and can only be used where the flow rate is sufficient to provide torque. A unique advantage is that it can be used on rivers' surfaces, and can even be movable, if it is placed in an anchored boat. The fountains of King Louis XIV 's summer residence, the Palace Of Versailles were powered by a large permanent installation of undershot wheels. MODERN VERSIONS A more modern version combines features of both: the Banki Turbine . In this version the water stream is "dug out" below the wheel, and pushes open-bottomed buckets. It captures energy from both the top, and then the water drains to the bottom of the wheel and pushes the bottom as well. This version captures power from both the flow and the weight, and became the most popular version throughout Europe. It is still a very practical low-technology hydropower design. Water wheels used shafts driving belts to transmit power from the wheel to machinery. One wheel could be used to power many machines, and sometimes even different mills. A fine advantage of the shaft technology was that the shaft could go through a Bearing in a load-bearing wall. This both supported the wheel and let most of the Machinery be indoors, where it is protected from the elements. Usually the main Axle Bearing could be lubricated from inside. The shaft would usually drive a Pulley which in turn would drive a leather Belt . The belt could drive any of a set of other shafts ( Axle s). Correctly-sized Pulley s adapted the Torque and speed of the wheel to the torque and speed needed by each piece of machinery. In other cases, the machinery was driven directly from the the wheel shaft, sometimes via gearing. Modern installations for "waterwheel" sites tend to use small weatherproof Kaplan Turbine s. These are purchased from the manufacturer and installed, sometimes in groups. The higher efficiencies permit smaller, less expensive Dam s, and use with smaller streams or smaller flumes than historic waterwheels. These usually have integral Electric Generator s. WATER WHEEL TECHNOLOGY The Technology of the water wheel had long been known, but it was not put into widespread use until the Middle Ages when an acute shortage of labour made machines such as the water wheel cost effective. Cistercian Monasteries , in particular, made extensive use of water wheels to power Watermills of many kinds. Grist mills (for corn) were undoubtedly the most common, but there were also sawmills, fulling mills and mills to fulfil many other labor-intensive tasks. The water wheel remained competitive with the Steam Engine well into the Industrial Revolution . Water wheel technology was developed extensively in in Leek, Staffordshire , England . In the 19th Century , Jean-Victor Poncelet worked on improving the efficiency of the undershot design using modern hydraulic physics for the first time. The main difficulty of water wheels was their inseperability from water. This meant that mills often needed to be located far from population centres and away from natural resources. Water mills were still in commercial use well into the twentieth century, however. Overshot & pitchback waterwheels are suitable where there is a small stream with a height difference of more than 2 metres, often in association with a small reservoir. Breastshot and undershot wheels can be used on rivers or high volume flows with large reservoirs. The most powerful waterwheel built in the United Kingdom was the 100 hp Quarry Bank Waterwheel near Manchester. A high breastshot design, it was retired in 1904 and replaced with several turbines. It has now been restored. Modern Hydro-electric Dam s can be viewed as the descendants of the water wheel as they too take advantage of the movement of water downhill. SEE ALSO
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