Watermill: Difference between revisions

A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour or lumber production, or metal shaping (rolling, grinding or wire drawing). A watermill that generates electricity is usually called a hydroelectric plant.

The ancient Greeks and Romans are known to have used the technology. In the 1st century BC, the Greek epigrammatist Antipater of Thessalonica made the first clear reference to the waterwheel. He praised it for its use in grinding grain and the reduction of human labour:^[1]

Hold back your hand from the mill, you grinding girls; even if the cockcrow heralds the dawn, sleep on. For Demeter has imposed the labours of your hands on the nymphs, who leaping down upon the topmost part of the wheel, rotate its axle; with encircling cogs^[2], it turns the hollow weight of the Nisyrian millstones. If we learn to feast toil-free on the fruits of the earth, we taste again the golden age.

However, Lewis has argued that the water wheel, probably at least the vertical kind, was included in post portions of the Philo of Byzantium, who wrote in the 3rd century BC, and parts of whose work survives in Arabic and Latin translations, including that of Vitruvius. An early exapmle is mentioned in Strabo's Geography near the palace at Cabira of Mithradates VI Eupator, King of Pontus from 120 BC to 71 BC and 67 BC to 66 BC. The fulling mill and mills for pounding grain (to dehusk it) seem also to have been used in the Roman Empire.^[3]

The Romans used both fixed and floating water wheels and introduced water power to other countries of the Roman Empire. So-called 'Greek Mills' used water wheels with a horizontal wheel (and vertical shaft). A "Roman Mill" features a vertical wheel (on a horizontal shaft). Greek style mills are the older and simpler of the two designs, but only operate well with high water velocities and with small diameter millstones. Roman style mills are more complicated as they require gears to transmit the power from a shaft with a horizontal axis to one with a vertical axis. An example of a Roman era watermill would be the early 4th century site at Barbegal (q.v.) in southern France, where 16 overshot waterwheels were used to power an enormous flour mill. There was also a mill on the Janiculum (q.v.) hill at Rome. Nevertheless Roman mills were few in number.

The watermill was separately invented in China during the Han dynasty (202 BC - 220 AD) in order to pound grain (to dehusk it) as well as to power piston bellows of a blast furnace in forging cast iron.

In the text known as the Xin Lun written by Huan Tan about 20 AD (during the usurpation of Wang Mang), it states that the legendary mythological king known as Fu Xi was the one responsible for the pestle and mortar, or tilt-hammer device (see trip hammer). Although the author speaks of the mythological Fu Xi, a passage of his writing gives hint that the waterwheel was in widespread use by the 1st century AD in China (Wade-Giles spelling):

Fu Hsi invented the pestle and mortar, which is so useful, and later on it was cleverly improved in such a way that the whole weight of the body could be used for treading on the tilt-hammer (tui), thus increasing the efficiency ten times. Afterwards the power of animals—donkeys, mules, oxen, and horses—was applied by means of machinery, and water-power too used for pounding, so that the benefit was increased a hundredfold.^[4]

In 31 AD, a Chinese engineer named Du Shi (Wade-Giles: Tu Shih) "invented the first water-powered bellows. This was a complicated machine containing gears, axles, and levers that was powered by a waterwheel," ^[5]. In essence, Du Shi's invention aided the forging of cast iron smelted from the blast furnace. Du Shi's invention was continued by Chinese living in subsequent dynastic periods of China, although the bellows of his device were improved upon in later periods (from leather bellows to wooden-fan bellows).^[6] Early Chinese mills had horizontal wheels.

In a 2005 survey the scholar Adam Lucas identified the following first appearances of various industrial mill types in Western Europe. Noticeable is the preeminent role of France in the introduction of new innovative uses of waterpower. However, he has drawn attention to the dearth of studies of the subject in several other countries. However he points to a lack of studies in otehr regions.

Typically, water is diverted from a river or impoundment or mill pond to a turbine or water wheel, along a channel or pipe (variously known as a flume, head race, mill race, leat, leet,^[8] lade (Scots) or penstock). The force of the water's movement drives the blades of a wheel or turbine, which in turn rotates an axle that drives the mill's other machinery. Water leaving the wheel or turbine is drained through a tail race, but this channel may also be the head race of yet another wheel, turbine or mill. The passage of water is controlled by sluice gates that allow maintenance and some measure of flood control; large mill complexes may have dozens of sluices controlling complicated interconnected races that feed multiple buildings and industrial processes.

Watermills can be divided into two kinds, one with a horizontal waterwheel on a vertical axle, and the other with a vertical wheel on a horizontal axle. The oldest of these were horizontal mills in which the force of the water, striking a simple paddle wheel set horizontally in line with the flow turned a runner stone balanced on the rynd which is atop a shaft leading directly up from the wheel. The bedstone does not turn. The problem with this type of mill arose from the lack of gearing; the speed of the water directly set the maximum speed of the runner stone which, in turn, set the rate of milling.

Most watermills in Britain and the United States of America had a vertical waterwheel, one of three kinds: undershot, overshot and breast-shot. This produced rotary motion around a horizontal axis, which could be used (with cams) to lift hammers in a forge, fulling stocks in a fulling mill and so on. However, in corn mills rotation about a vertical axis was required to drive its stones. The horizontal rotation was converted into the vertical rotation by means of gearing, which also enabled the runner stones to turn faster than the waterwheel. The usual arrangement in British and American corn mills has been for the waterwheel to turn a horizontal shaft on which is also mounted a large pit wheel. This meshes with the wallower, mounted on a vertical shaft, which turns the (larger) great spur wheel (mounted on the same shaft). This large face wheel, set with pegs, in turn, turned a smaller wheel (such as a lantern gear) known as a stone nut, which was attached to the shaft that drove the runner stone. The number of runner stones that could be turned depended directly upon the supply of water available. In many mills the great spur wheel turned only one stone, but there might be several mills under one roof. As waterwheel technology improved mills became more efficient, and by the 19th century, it was common for the great spur wheel to drive several stone nuts, so that a single water wheel could drive as many as four stones.^[9] Each step in the process increased the gear ratio which increased the maximum speed of the runner stone. Adjusting the sluice gate and thus the flow of the water past the main wheel allowed the miller to compensate for seasonal variations in the water supply. Finer speed adjustment was made during the milling process by tentering, that is, adjusting the gap between the stones according to the water flow, the type of grain being milled, and the grade of flour required.

The overshot wheel was a later innovation in waterwheels and was around two and a half times more efficient than the undershot.^[10] The undershot wheel, in which the main water wheel is simply set into the flow of the mill race, suffers from an inherent inefficiency stemming from the fact that the wheel itself, entering the water behind the main thrust of the flow driving the wheel, followed by the lift of the wheel out of the water ahead of the main thrust, actually impedes its own operation. The overshot wheel solves this problem by bringing the water flow to the top of the wheel. The water fills buckets built into the wheel, rather than the simple paddle wheel design of undershot wheels. As the buckets fill, the weight of the water starts to turn the wheel. The water spills out of the bucket on the down side into a spillway leading back to river. Since the wheel itself is set above the spillway, the water never impedes the speed of the wheel. The impulse of the water on the wheel is also harnessed in addition to the weight of the water once in the buckets. Overshot wheels require the construction of a dam on the river above the mill and a more elaborate millpond, sluice gate, mill race and spillway or tailrace.^[11]

Toward the end of the 19th century, the invention of the Pelton wheel encouraged some mill owners to replace over- and undershot wheels with penstocks and Pelton wheel turbines. By the early 20th century, availability of cheap electrical energy made the water mill obsolete; although in North America, some smaller rural mills continued to operate commercially into the 1960s. A few historic mills (for example, at the Wayside Inn) still operate for demonstration purposes to this day.

A unique type of water mill is the tide mill. This mill might be of any kind, undershot, overshot or horizontal but it does not employ a river for its power source. Instead a mole or causeway is built across the mouth of a small bay. At low tide, gates in the mole are opened allowing the bay to fill with the incoming tide. At high tide the gates are closed, trapping the water inside. At a certain point a sluice gate in the mole can be opened allowing the draining water to drive a mill wheel or wheels. This is particularly effective in places where the tidal differential is very great, such as the Bay of Fundy in Canada where the tides can rise fifty feet, or the now derelict village of Tide Mills in the UK.

Other water mills can be set beneath large bridges where the flow of water between the stanchions is faster. At one point London bridge had so many water wheels beneath it that bargemen complained that passage through the bridge was impaired.

A final, rather elegant, water wheel innovation places the wheel in a boat anchored in midstream. The flow of the river past the boat turns the wheel and drives the millstone.

"Run of the river" schemes do not divert water at all and usually involve undershot wheels, and some types of water wheel (usually overshot steel wheels) mount a toothed annular ring near the outer edge that drives machinery from a spur gear rather than taking power from the central axle. However, the basic mode of operation remains the same; gravity drives machinery through the motion of flowing water.

17th century water mill

The sounds of the mechanism grinding flour.

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• Gristmills grind grains into flour. These were undoubtedly the most common kind of mill.
• fullings or Walkmills were used for a finishing process on cloth.
• Sawmills cut timber into lumber.
• Bark Mills stripped bark from trees or ground it to powder for use in tanneries.
• Spoke mills turned lumber into spokes for carriage wheels.
• At the beginning of the industrial revolution, cotton mills were usually powered by a water wheel.
• Bobbin Mills made wooden bobbins for the cotton and other textile industries.
• Carpet mills for making rugs were sometimes water-powered.
• Textile mills for weaving cloth were sometimes water-powered.
• Powder mills for making gunpowder - black powder or smokeless powder were usually water-powered.
• Blast Furnaces, finery forges, slitting mills, and tinplate works were until the introduction of the steam engine invariably water powered. Furnaces and Forges were sometimes called iron mills.
• Blade mills were used for sharpening newly made blades.
• Prior to the introduction of the cupola (a reverberatory furnace), lead was usually smelted in smeltmills.
• Paper mills used water not only for motive power, but also required it in large quantities in the manufacturing process.

• Hydropower
• Micro hydro
• Renewable Energy
• Watermills in the United Kingdom
• Water wheel
• Millstone
• Molinology
• The International Molinological Society
• Sustainable living
• Scottish Rural Life, History Dictionary - a Dictionary which includes many milling terms.(right)

• Woods, Michael and Mary (2000). Ancient Machines: From Wedges to Waterwheels. Minneapolis: Twenty-First Century Books.
• Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 2. Taipei: Caves Books, Ltd.
• Reynolds, Terry S. Stronger Than a Hundred Men: A History of the Vertical Water Wheel. (Johns Hopkins University Press 1983). ISBN 0801872480.

• 17 Jun 2003, Deutsche Welle: The World's First Underwater Windmill Starts Turning
• U.S. Mill Pictures and Information
• Tidal power station
• Mill database with over 10000 european mills
• Watermills in Norfolk, England
• Mills in Hampshire, England
• Upwey Mill, Weymouth, Dorset
• The International Molinological Society (TIMS)
• The Society for the Preservation of Old Mills (SPOOM)