A water mill is a mostly historical technical system that is driven by water power by means of a water power machine and uses the kinetic energy of the water. The system can be a mill in the narrower sense, in which something is ground or comminuted ( grinding mill ), or a mill in which other machines are driven (e.g. hammer mill , saw mill , grinding mill , paper mill , Pumping station).
The water required for propulsion ( impact water ) is normally taken from a river . Depending on the local conditions, ponds , weirs , canals or other hydraulic structures are required to increase the drop height and to store water , see also battle (hydraulic structures) .
Watermills are very old structures used by humans that were not powered by human or animal muscles. Water-powered bucket wheels for irrigation ("Noria") date back to the 5th century BC. Known from Mesopotamia . The first water-powered grinding mills are from the 3rd century BC. From Asia ( China ) attested. The ancient Egyptians , Persians and later the Greeks and Romans also used water mills, as is known from a poem by Antipater of Thessalonica , a travelogue by the geographer Strabo or the detailed technical descriptions of Philo of Byzantium or Vitruvius .
The Hierapolis sawmill was a water-powered stone saw dated to the second half of the 3rd century AD, for the first time with a crankshaft and connecting rod . Vitruvius and Pliny the Elder already reported on marble slabs as wall cladding in the house of the Solos of the Mouse (d. 351 BC) in Halicarnassus . At the Temple of Artemis in Gerasa (Jordan) (6th century AD), the remains of a water-powered stone sawmill with two opposing frame saws with four saw blades each were found.
The Romans also brought watermill technology to Germany, as can be seen from a find near Düren in the Rhineland from the time around the birth of Christ. In a travel report Mosella from the year 368, the Roman official Ausonius mentions the first watermills on the Kyll and Ruwer , tributaries of the Moselle. In the Franconian people's law Lex Salica from around 450 water mills with a dam (Farinarius) are mentioned. The oldest archaeologically proven watermills in Germany are from the 1st century in Düren, from the year 156 in Etting and one from the 6th century in the Alemannic settlement Mittelhofen near Lauchheim .
In 2005, during an archaeological excavation in the Rotbachtal near Erftstadt-Niederberg (North Rhine-Westphalia, Kr. Düren), the remains of a watermill built in 833 AD were discovered. The waterwheel of the system, which was operated under-cut, could be reconstructed to a diameter of around 1.65 m and was in operation for several decades.
From the Middle Ages onwards , water wheels were used to drive grinding mills and various other machines throughout Western and Central Europe as far as the North and Baltic Sea region.
With increasing spread, the rulers and landlords used the water mills as a source of income for taxes. In addition to the mill right and the mill compulsory , which applied to mills with drives of all kinds and especially to grain mills, some additional regulations were important for water mills: A special fee was usually due for the use of the damming right ( water knowledge , water interest , ...).
From the 17th century, hydropower-powered machines (" water art ") were also used extensively in mining and in pre-industrial trades. With industrialization , water mills, like wind and Göpel mills, increasingly competed with flexible and powerful steam mills , with combustion engines and finally with electrically driven mills. The large industrial mills more and more replaced the small, classic craft mills; these became uneconomical, so that at the end of the 19th century there was a "mill death".
With increasing electrification , those water mills that remained in operation often switched their water power drive from the water wheel to one of the newly developed, more effective water turbines , which generated electricity by means of a generator to drive the electrical machines in the mill ( turbo-electric drive ). Surplus could be fed into the electrical network. The latter function was often the main purpose after milling was abandoned; the former water mill became a pure hydroelectric power station .
After many water mills and windmills had already been shut down and demolished, in the middle of the 20th century the importance of these structures as technical monuments was reflected . Some of the mills could be preserved in more or less original condition as a technology museum or for other purposes (often as a restaurant or similar).
Since the end of the 20th century, historical water mills have been increasingly revitalized and converted into small hydropower plants as part of the increased importance of climate-neutral renewable energies . The basis for this is provided by modern water wheels, which preserve the historical character of the mill and thus do justice to monument protection, but which are hardly inferior to water turbines in their effectiveness.
Structure and technology
The height of fall, the flow velocity, the amount of water and the efficiency are decisive for the achievable performance of a water mill.
A watermill structure usually consists of three parts, which are explained below:
- Hydraulic structures for guiding and storing the impact water
- Drive consisting of a water power machine (water wheel, water turbine) and the power transmission to the machine
- Production plant (mill in the narrower sense) with the grinders or other working machines
The simplest form of the water mill is the one in which the mill is placed directly on the bank of the driving flowing water without changing its course. In extreme cases, the mill can even float on the surface of the water as a ship's mill . The water is neither diverted nor dammed, the water wheel only plunges into the water with the blades on the underside ( deep or undershot mill wheel). However, such mills are not very efficient and they accordingly require a wide mill wheel and a larger river that always carries enough water.
In order to be able to set up water mills on watercourses with little water or with a slight gradient, it is necessary to increase the power of the water by increasing the height of fall and thus the impulse / pressure of the impact water. The water wheel is acted upon by the power water from the side at the height of the wave ( medium shaft ) or from above ( overshot ).
The height of the fall is increased either by branching off part of the current of the driving watercourse and running it in parallel in a canal (often called "Mühlengraben") or , more rarely, over an elevated channel or an underground tunnel with a lower gradient. When the desired height difference is reached, the water is led over the mill wheel and added to the watercourse.
The other way to increase the height of fall is to impound the watercourse through a dam or weir . The barrage , also called mill jam, has the positive effect of increasing the height of the fall and storing water in the reservoir ( mill pond ) , which can be accessed when required. The mill is less dependent on the water level in times when the watercourse that feeds it has little water.
Particularly in mining, great effort was made to store and guide the power water for the water arts, and in some cases widespread systems of reservoirs ( artificial ponds ) , canals ( artificial ditches ) and tunnels ( Rösche , watercourse ) were created. Well-known examples of such systems are the Oberharzer Wasserregal or the Freiberg district water supply .
The flow energy of the water is converted into mechanical work with a water power machine. Water wheels are mostly used for this. A distinction is made between overshot and undershot water wheels. When the water wheel is overshot, the water flows over the top of the wheel and turns it quickly against the direction of flow due to the gradient. With the undershot water wheel, the lower part of the wheel is in the river and this turns the wheel slowly and powerfully in the direction of the flow.
The gnepfen , which were very simple in construction but not very effective, were only used in rare special cases . A gneapple is a seesaw with a bucket on one end that is filled at the top, moving down and being emptied at the bottom. The resulting tilting movement is used in a striking mechanism.
From the 19th century, water motors derived from steam engines were also found, especially in mining .
Mill / production equipment
As with other mills, water mills can also be mills in the narrower or broader sense. That means either something is ground or comminuted here (e.g. grain mill , oil mill , gypsum mill ) or the water power is used to drive various machines (e.g. saw mill , hammer mill , grinding bowl ). The latter use was more common with watermills than with windmills or Göpelmühlen.
Advantages and disadvantages compared to other types of mills
Compared to other types of mills, water mills have a number of advantages and disadvantages:
The greatest advantage of hydropower is that it is available as a natural and renewable energy source (except when there is persistent frost) in principle unlimited and free of charge. This also applies to windmills as they compete with water mills; however, these are more dependent on the weather than water mills. Of course, the amount of available impact water is also dependent on seasonal fluctuations in the amount of precipitation, even with water mills, but these do not change as quickly as the wind and, unlike the wind, the water can be dammed, stored in a mill pond and accessed from there as needed .
The condition for the use of hydropower is that there is a body of water with a sufficient gradient that carries enough water even in dry periods. Since this condition is not met in many places in the lowlands, where the wind was often stronger and more evenly blown, the windmill has established itself as the predominant type of mill in the coastal, flat regions, and the water mill in the more mountainous regions.
The operation of watermills is problematic in areas in which there is constant frost in winter, since watermill operation is not possible at times when the flowing water on which the mill in question is located is icy.
An attempt to combine the advantages of wind and water mill, the wind water mill . This hybrid form is only suitable for a few locations, there are only a few mills of this type.
An attempt was made to adapt watermills to the local supply of power water by means of some special designs:
- Tide mill - not driven by flowing water, but by tidal currents (ebb and flow)
- Ship mill - floating mill with a deep mill wheel
- Wind watermill - combination of a watermill with a windmill
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