Water wheel

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For water wheels used to drive boats, see paddle wheel. For wheels used solely to lift water see noria. For factories or industries driven by water wheels see watermill.

An overshot water wheel standing 42 feet high powers the Old Mill at Berry College in Rome, Georgia

A water wheel is a hydropower system; a machine for extracting power from the flow of water. Water wheels and hydropower was widely used 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 in gristmills, but other uses included foundry work and machining, and pounding linen for use in paper.

A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface. Most commonly, the wheel is mounted vertically on a horizontal axle, but the tub or Norse wheel is mounted horizontally on a vertical shaft. Vertical wheels can transmit power either through the axle or via a ring gear and typically drive belts or gears; horizontal wheels usually directly drive their load. A channel created for the water to follow after leaving the wheel is commonly referred to as a "tailrace."^[1]

1 History of Water Wheel Technology
2 Types
3 Notes
4 See also
5 External links

[edit] History of Water Wheel Technology

Main article: Watermills

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 labor made machines such as the water wheel cost effective. However, the water wheels in ancient Rome and ancient China found many practical uses in powering mills for pounding grain and other substances. The Romans used both fixed and floating water wheels and introduced water power to other countries of the Roman Empire. The Romans were known to use waterwheels extensively in mining projects, with enormous Roman-era waterwheels found in places like modern-day Spain. In the 1st century BC, the Greek epigrammatist Antipater of Thessalonica was the first to make a reference to the waterwheel. He praised it for its use in grinding grain and the reduction of human labor:

Cease from grinding, oh you toilers; women slumber still, Even if the crowing rooster calls the morning star. For Demeter has appointed nymphs to turn your mill, And upon the waterwheel alighting here they are. See how quick they twirl the axle whose revolving rays spin heavy rollers quarried overseas. So again we savor the delights of ancient days, Taught to eat the fruits of Mother Earth in ease.

The 1st century Chinese of the Eastern Han Dynasty began to use waterwheels to power the piston-bellows in forging iron ore into cast iron (for more info, see the article on Du Shi). Waterwheels in China found practical uses such as this, as well as extraordinary use. The inventor Zhang Heng (78 - 139) was the first in history to apply motive power in rotating the astronomical instrument of an armillary sphere, by use of a waterwheel. The mechanical engineer Ma Jun (200 - 265) once used a waterwheel to power and operate a large mechanical puppet theater for Emperor Ming of Wei.

Cistercian monasteries, in particular, made extensive use of water wheels to power watermills of many kinds. An early example of a very large waterwheel is the still extant wheel at the early 13th century Real Monasterio de Nuestra Senora de Rueda, a Cistercian monastery in the Aragon region of Spain. Grist mills (for corn) were undoubtedly the most common, but there were also sawmills, fulling mills and mills to fulfill many other labor-intensive tasks. The water wheel remained competitive with the steam engine well into the Industrial Revolution.

The main difficulty of water wheels was their inseparability from water. This meant that mills often needed to be located far from population centers 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 meters, 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 Mill Waterwheel near Manchester. A high breastshot design, it was retired in 1904 and replaced with several turbines. It has now been restored and is a museum open to the public.

Modern Hydro-electric dams can be viewed as the descendants of the water wheel as they too take advantage of the movement of water downhill.

[edit] Types

[edit] Undershot wheel

Undershot water wheel

A vertically mounted water wheel that is rotated by water striking paddles or blades at the bottom of the wheel is said to be undershot. This is generally the least efficient, oldest type of wheel (with the exception of the poncelet wheel). 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.

Undershot wheels gain no advantage from head and are never backshot. They are most suited to shallow streams in flat country.

The Anderson Mill is undershot, backshot, and overshot using two sources of water. This allows the speed of the wheel to be controlled

Undershot wheels are also well suited to installation on floating platforms, and the Romans mounted them immediately downstream from bridges where the flow restriction of arched bridge supports increased the speed of the current.

[edit] Backshot wheel

An overshot wheel is backshot by introducing the intake water from the same direction as the flow of the output water, sometimes by the introduction of a 180 degree turn just past the wheel itself, and some times through a lengthy flume or penstock configuration dictated by the surrounding terrain.

A backshot wheel continues to function until the water in the wheel pit rises well above the height of the axle, when any other overshot wheel will be stopped or even destroyed. This makes the technique particularly applicable in streams that experience extreme seasonal variations in flow, and reduces the need for complex sluice and tail race configurations. A backshot wheel may also gain power from the water's current past the bottom of the wheel, and not just the weight of the water falling in the wheel's buckets.

Backshot water wheels are also often referred to as pitchback or Mid-Wheels.

[edit] Breastshot wheel

A vertically mounted water wheel that is rotated by falling water striking buckets near the center of the wheel's edge, or just above it, is said to be breastshot. Breastshot wheels are the most common type in the United States of America and are said to have powered the American industrial revolution.

Breastshot wheels are less efficient than overshot wheels, more efficient than undershot wheels, and are not backshot. The individual blades of a breastshot wheel are actually buckets, as are those of most overshot wheels, and not simple paddles like those of most undershot wheels (the Poncelet design being a notable exception). A breastshot wheel requires a good trash rake and typically has a masonry "apron" closely conforming to the wheel face, which helps contain the water in the buckets as they progress downwards. Breastshot wheels are preferred for steady, high-volume flows such as are found on the fall line of the North American East Coast.