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Watermill
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A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour, lumber or textile production, or metal shaping (rolling, grinding or wire drawing).
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A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour, lumber or textile production, or metal shaping (rolling, grinding or wire drawing). A watermill that generates electricity is usually called a hydroelectric plant.
History
Ancient Mesopotamia
In ancient Mesopotamia, irrigation machines are referred to in Babylonian inscriptions, but without details on their construction, suggesting that water power had been harnessed for irrigation purposes. The primitive use of water-rotated wheels may date back to Sumerian times, with references to a "Month for raising the Water Wheels", though it is not known whether these wheels were turned by the flow of a river.
Greco-Roman world
The earliest clear evidence for the use of water for powering mills dates back to the ancient Greco-Roman world. The British historian of technology M. J. T. Lewis has shown that portions of Philo of Byzantium's mechanical treatise, which describe water wheels, and which have been previously regarded as later Arabic interpolations, actually date back to the Greek 3rd century BC original. The Greek author Strabo mentions in his Geography another early watermill, located near the palace of king Mithradates VI Eupator (r. 120-63 BC) at Cabira. In the early 1st century BC, the Greek epigrammatist Antipater of Thessalonica made the first clear reference to the waterwheel which he praised for its use in grinding grain and the reduction of human labour. It should be noted that this mill was already of the advanced vertical type featuring gears:
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,' 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.
Mills were commonly used for grinding grain into flour (attested by Pliny the Elder), but industrial uses as fulling and sawing marble were also applied, evidenced by a quotation from the fourth century AD author Ausonius.
The Romans used both fixed and floating water wheels and introduced water power to other provinces 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.
A particularly large and sophisticated Roman era watermill is the 2nd century site at Barbegal in southern France. This complex, which has been described as "the greatest known concentration of mechanical power in the ancient world", featured 16 overshot waterwheels to power an equal number of flour mills. The capacity of the mills has been estimated at 4.5 tons of flour per day, sufficient to supply enough bread for the 12,500 inhabitants occupying the town of Arelate at that time. A similar mill complex existed on the Janiculum hill, whose supply of flour for Rome's population was judged by emperor Aurelian important enough to be included in the Aurelian walls in the late 3rd century. Much later in 537 AD, ship mills were ingeniously used by the East Roman general Belisarius, when the besieging Goths cut off the water supply for those mills.
Although to date only a few dozen Roman mills are archaeologically traced, the widespread use of aqueducts in the period suggests that many remain to be discovered. Recent excavations in Roman London, for example, have uncovered what appears to be a tide mill together with a possible sequence of mills worked by an aqueduct running along the side of the River Fleet.
Water lifting machines were common during the Roman period to dewater deep underground mines. Several such devices are described by Vitruvius, including the reverse overshot water-wheel and the Archimedean screw. Many were found during modern mining at the copper mines at Rio Tinto in Spain, one system involving 16 such wheels stacked above one another so as to lift water about 80 feet from the mine sump. Part of such a wheel was found at Dolaucothi, a Roman gold mine in south Wales in the 1930s when the mine was briefly re-opened. It was found about 80 feet below the surface, so must have been part of a similar sequence as that discovered at Rio Tinto. It has recently been carbon dated to about 80 AD, and since the wood from which it was made is much older than the deep mine, it is likely that the deep workings were in operation perhaps 30-50 years after. It is clear from these examples of drainage wheels found in sealed underground galleries in widely separated locations that building water wheels was well within their capabilities, and such verticals water wheels commonly used for industrial purposes.
Ancient China
A different variety of watermill was known in China during the Han dynasty (202 BC - 220 AD), but initially only in order to pound grain (to dehusk it).
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 suggests 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.
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," according to Mary and Michael Woods. 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). Early Chinese mills featured mostly horizontal wheels, but vertical wheels were also employed.
Ancient India
The early history of the watermill in India is obscure. Ancient Indian texts dating back to the 4th century BC refer to the term cakkavattaka (turning wheel), which commentaries explain as arahatta-ghati-yanta (machine with wheel-pots attached). On this basis, Joseph Needham suggested that the machine was a noria. Terry S. Reynolds, however, argues that the "term used in Indian texts is ambiguous and does not clearly indicate a water-powered device." Thorkild Schiøler argued that it is "more likely that these passages refer to some type of tread- or hand-operated water-lifting device, instead of a water-powered water-lifting wheel."
Irrigation water for crops was provided by using water raising wheels, some driven by the force of the current in the river from which the water was being raised. This kind of water raising device was used in ancient India.
Around 1150, the astronomer Bhaskara Acharya observed water-raising wheels and imagined such a wheel lifting enough water to replenish the stream driving it, effectively, a perpetual motion machine.
The construction of water works and aspects of water technology in India is described in Arabic and Persian works. During medieval times, the diffusion of Indian and Persian irrigation technologies gave rise to an advanced irrigation system which bought about economic growth and also helped in the growth of material culture.
Islamic world
Muslim engineers adopted the water wheel technology from the hydraulic societies of the ancient Near East, where it had been applied for centuries prior to the Muslim conquests. As early as the 7th century, excavation of a canal in the Basra region discovered remains of a water wheel dating from this period. Hama in Syria still preserves one of its large wheels, on the river Orontes, although they are no longer in use. The largest had a diameter of about 20 metres and its rim was divided into 120 compartments. Another wheel that is still in operation is found at Murcia in Spain, La Nora, and although the original wheel has been replaced by a steel one, the Moorish system during al-Andalus is otherwise virtually unchanged. The flywheel mechanism, which is used to smooth out the delivery of power from a driving device to a driven machine, was invented by Ibn Bassal (fl. 1038-1075) of al-Andalus, who pioneered the use of the flywheel in the chain pump (saqiya) and noria.
The industrial uses of watermills in the Islamic world date back to the 7th century, while horizontal-wheeled and vertical-wheeled water mills were both in widespread use by the 9th century. A variety of industrial watermills were used in the Islamic world, including gristmills, hullers, paper mills, sawmills, shipmills, stamp mills, steel mills, sugar mills, and tide mills. By the 11th century, every province throughout the Islamic world had these industrial watermills in operation, from al-Andalus and North Africa to the Middle East and Central Asia. Muslim engineers also used crankshafts and water turbines, gears in watermills and water-raising machines, and dams as a source of water, used to provide additional power to watermills and water-raising machines. Fulling mills, paper mills and steel mills may have spread from Islamic Spain to Christian Spain in the 12th century. Industrial water mills were also employed in large factory complexes built in al-Andalus between the 11th and 13th centuries.
Muslim engineers used two solutions to achieve the maximum output from a water mill. The first solution was to mount them to piers of bridges to take advantage of the increased flow. The second solution was the shipmill, a type of water mill powered by water wheels mounted on the sides of ships moored in midstream. This technique was employed along the Tigris and Euphrates rivers in 10th century Iraq, where large shipmills made of teak and iron could produce 10 tons of flour from corn every day for the granary in Baghdad.
In the 13th century, Muslim engineers al-Jazari and Taqi al-Din depicted many water-raising machines in their technological treatises.
Medieval Europe
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.
| First Appearance of Various Industrial Mills in Medieval Europe, AD 770-1443 |
|---|
| Type of mill | Date | Country |
|---|
| Malt mill | 770 | France | | Fulling mill | 1080 | France | | Tanning mill | ca. 1134 | France | | Forge mill | ca. 1200 | England, France | | Tool-sharpening mill | 1203 | France | | Hemp mill | 1209 | France | | Bellows | 1269, 1283 | Slovakia, France | | Sawmill | ca. 1300 | France | | Ore-crushing mill | 1317 | Germany | | Blast furnace | 1384 | France | | Cutting and slitting mill | 1443 | France | |
An early tide mill was recently excavated at the Nendrum Monastic Site in Northern Ireland. The complex is dated by dendrochronology to 787 AD.
Operation of a watermill
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, 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. 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. 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.
In many mills (including the earliest) the great spur wheel turned only one stone, but there might be several mills under one roof. The earliest illustriation of a single waterwheel driving more than one set of stones was drawn by Henry Beighton in 1723 and published in 1744 by J. T. Desaguliers.
The overshot wheel was a later innovation in waterwheels and was around two and a half times more efficient than the undershot. 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.
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.
"Run of the river" schemes
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.
A different 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. A working example can be seen at Eling Tide Mill.
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.
Watermills today
By the early 20th century, availability of cheap electrical energy made the water mill obsolete in developed countries although some smaller rural mills continued to operate commercially into the 1960s. A few historic mills (for example, at the Wayside Inn (USA)) still operate for demonstration purposes to this day, or even maintain small-scale commercial production as at Daniels Mill, Shropshire , Little Salkeld and Redbournbury Mill (All UK).
Some old mills are being upgraded with modern Hydropower technology, for example those worked on by the South Somerset Hydropower Group in the UK.
In some developing countries water mills are still widely used for processing grain. For example, there are thought to be 25,000 operating in Nepal, and 200,000 in India. Many of these are still of the traditional style, but some have been upgraded by replacing wooden parts with better-designed metal ones to improve the efficiency. For example, the upgraded 2,400 mills between 2003 and 2007.
Types of watermills
See also
External links
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