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Types of Vertical Water Wheels

A Model of a Pitch-Back Water Wheel.

Types of Vertical Water Wheels

Types of Vertical Water Wheels

Please Note: Today (Monday, 22, April 2002) I had a main storage drive crash. I had over 900 MB of stuff, and was the last back up for my computer that crashed last October. I lost the only copy of every mill and related mill site (that I have ever visited on the internet with all of the text and images); scanned images and artwork; HABS-HAER mill files; 30 years of manuscripts, writing projects and restoration reports; future web page material and business records. The follow is a "draft only copy" of the original intended article. When I recover from loosing heart and hating computer technology a bit less, perhaps I may issue a revised "final edition copy" with intended images and artwork. Thank you, T. R. Hazen.

Types of Vertical Water Wheels

The vertical water wheels has three main types- (1) the overshot (including the overshot and pitch-back varieties); (2) the breast shot (including the low, middle and high breast shot varieties); (3) the undershot (including the undershot and flutter wheel). The names indicate the point at which the water enters the wheel. If you look at and face the water wheel from the side and regard it as a clock face. Then only the overshot would revolve in a clockwise direction while the pitch-back, the breast shot and undershot water wheels revolve in an counterclockwise direction.

The development of the mechanized factories both in England and the United states led to efforts to improve the efficiency of existing water wheels. The British engineer named John Smeaton in the eighteen century analyzed the relative efficiency of two forms of water wheels, the undershot and the overshot. "The average overshot wheel was far more efficient than the undershot, about 65% as opposed to 25%. The undershot wheel is an impulse wheel, since the water imparts its energy by pushing. If the hillside is steep, the water moves fast at the bottom and can push impressively against the paddles of an undershot wheel. The overshot wheel is a gravity wheel. It is a series of buckets attached to the outside of a big circle. The water goes into a container at the top and drops all the way down." In the 1840's the Franklin Institute conducted tests in the United States, probing the efficiencies of water wheels once and for all.

The overshot water wheel directs is water onto the wheel to turn in the same direction without changing its direction. They are usually used on falls of over ten feet. The water is conveyed to the top of the wheel by a wooden trough or sluice box and fed into the buckets. The water from the sluice box and the chute let the water into the buckets of the wheel from the control gate. The buckets are formed by boards set at an angle toward the stream and the ends or sides of the boards are set into slots in the sides of the wheel. The depth of the shrouds varied but usually it was from 9 to 15 inches. The bottom edges of the front bucket boards are fastened to the sole or drum formed by planks secured to the inside end of the shrouds. The seams are often covered with batten to prevent leakage of water. This type of water wheels is referred to as a bucket wheel. The power generated by an overshot water wheel depends almost entirely on the weight of the water in the buckets, and the forward momentum of the water as it enters the buckets adds slightly to the increment of the wheel's power.

The water wheel moves in the same direction of the stream. The wheel gets its benefit from the whole initial velocity and impulse of the water. The advantage will be lost of the bottom of the wheel is immersed in water and begins moving against the current. It is only possible for the wheel to turn above the tail water. It the bottom portion begins to become cover immersed in water this effect called back watering. In the case of an overshot water wheel it will obstruct and impede its movement because air becomes trapped in the buckets as the water wheel is rotating. The direction of that the overshot water wheel turns in back water tends to draw floating debris into the water wheel and do damage to it. Another great problem with overshot water wheels is that often the water is directed from the chute onto the wheel too far forward of the vertical center of the water wheel and too much water flies over the wheel and never enters the buckets.

The end of the water box and the end of the chute attached to it should be just behind the vertical center so when the water enters the wheel it is just behind the vertical center. In this way the wheel takes full advantage of the water and the fall available. The general rule for building an over shot water wheel is to allow a foot above and a foot below the wheel subtracted from the available fall. This will give you the largest water wheel that could be possibly be constructed. I said to allow a foot above the wheel but this does not mean that the water should ever drop upon the water wheel from the end of the chute by one foot. This is to allow the construction of the sluice box, water box and its supports behind the back curve of the water wheel on the upstream side only. The water should exit the chute and move only in the direction of the turning water wheel and the stream and not downward. One foot (or more) should be allow under the water wheel to allow the water to flow away from the water wheel. Then by the time the water flows down the tail race to pass the end of the building it should have dropped a total of three feet from the bottom of the water wheel.

If water is directed upon the water wheel not in the direction the water wheel rotates a phenomenon will develop known as "shock" which will retard and in many cases stop the water wheel from turning especially in water wheels that are out of balance. Generally only wooden water wheels suffer for being out of balance but rebuilt metal wheels sometimes also have this problem. The balance of the water wheel will greatly effect if ability to rotate properly. An out of balance water wheel will not rotate properly. If shock is effecting a wooden water wheel it will sit there for hours without turning unless it is given a "kick" start. An out of balance water wheel will slow in its rotation when it reaches an imbalance point. An out of balance wheel with out an internal load will sometimes begin to turn backwards and seesaw back and forth until it stops with the heavy end downward. A hidden water jet spray under the sluice box will wet the whole water wheel and help improve this problem. It should be turned off in the winter months to prevent ice on the water wheel.

One of the largest water wheel in the United States was the constructed by Henry Burden, a Scottish born iron worker, near Troy, New York. He built an over shot water wheel in 1851. It was 69 feet in diameter by 22 feet wide. It had a cast iron axle, wrought iron rods for spokes. The shrouding being made of cast iron sections, buckets of Georgia Pine, with iron reinforcing. The Burden wheel developed 278-280 horse power, with an efficiency of 80% to 84.25%. Today the largest remaining water wheel is the Fairwater Wheel, once part of the Fairwater Electric Company, Fair Water, Wisconsin. The largest water wheel constructed by the Fitz Water Wheel Company, Hanover, Pennsylvania. It is 50 Feet in diameter Steel Overshoot Water Wheel. Built in 1924, the 29 ton wheel is 10 feet wide, and produced about 140 horsepower. The largest vertical water wheels in the world are the Noria Water Wheels found in Syria and Jordan. They are located in Hama that is a river town, built on the banks of the Orontes. The town is famous for the 17 huge wooden water wheels, known as noria, which once scooped water from the river and deposited it into the aqueducts, which then supplied homes, public buildings and farms. These wheels are about 20 meters (90 feet) in diameter and still turn today, although their water is not used. The noria situated in the town center are located in a public park and the Four Norias of Bichriyat are situated on a weir about 1 kilometers up-river from the town center. The largest noria is known as Al-Mohammediyyah.

The pitch-back water wheel is another modification form of the overshot water wheel. This type of over shot water wheel the water is carried to the back of the water wheel or over the top of the wheel were it is introduced into the buckets and the water wheel turns in a pitch-back direction to that of which it was moving in the sluice box. The buckets of the pitch-back are set at an angle opposite to that of an overshot. The end of the sluice box and the control gate are adapted so that the water is fed downward into the buckets at the reverse direction to the flow of the stream, thus causing the wheel to revolve in the opposite direction. Behind the wheel is an arch of stone, wood or metal known as an apron, usually of the same radius at the wheel. The edge of the buckets run close to this apron to confine the water and prevent it form spilling from the buckets before arriving at the lowest point of the fall. Like the overshot water wheels the pitch-back water wheels derive most of their power from the weight of the water in the buckets, but they receive a certain amount of additional impulse from the water as it is fed in and changes direction from the gate.

The wheel thus runs in a contrary direction to that of the head stream, and in the turn (some have said) it looses some of the impulse of the water. The upper part of the water wheel may turn contrary to that of the stream but the lower part of the water wheel turns in the direction of the down stream, therefore the tail water is less immersed than the over shot. In this case the pitch-back is more like a larger breast shot water wheel than a true overshot. The pitch-back runs in the same direction as that of a breast shot and it may be arched into the wheel like that of a breast shot. Many of the back of the pitch-back have an arch, apron or shroud that helps hold the water into the wheel, and prevents winds from blowing it out.

The largest metal water wheel in the world is the Lady Isabella, the Laxey Wheel on the Isle of Man, United Kingdom, pitch-back water wheel 72 1/2 feet in diameter by 6 feet wide. The water wheel was connected to two arms that each operated cranks that pumped air into mines.

Breast Shot Water Wheel at the Grist Mill in Old Sturbridge Village.

The breast shot water wheel was the most common water wheel found powering American industry up until the 1840's when the French developed the water turbine from our application of the tub water wheel. In many cases the breast shot water wheels and undershot water wheels are of larger diameter than the overshot and pitch-back water wheels. The ordinary breast shot water wheel the water comes into the water wheel about at the center axis point. Some high breast shot water wheels the water is applied to the upward top of the water wheel. The weight of the water multiplied by the height of decent and not by just its impulse yields effective power. This type of water wheel has its lower upstream side or quarter encased by an arch or apron. It is made to fit closely to the rim of the water wheel to prevent the loss of water from moving under the wheel and thus keeping more water in the buckets keeping the water wheel more efficient.

The breast shot water wheel would have a wooden apron or breast behind the back one third of the water wheel. Once the water wheel is constructed or installed no one would be able to see this feature (but I think it should still be constructed). I would build the basic simplified frame work of wood but instead of using wooden boards or planks, I would use marine plywood screwed down the the wooden frame work. The wooden frame work underneath would be bolted into the concrete slap at the bottom of the water wheel pit so it would not move or lift up if the water wheel were to ever turn. The surface wood of the breast should be "one" inch away from the curve of the water wheel. This is why this work should be done with great care and thought.

A breast shot water wheel is most commonly used in falls of between 6 to 10 feet. These water wheels are constructed very similar to that of the overshot and pitch back design. Both often have elbow buckets. A breast shot is called a breast shot because behind and below where the water enters the water wheel is a breast or apron. These are usually fitted one inch away from the water wheel to retain the water in the buckets and make the water wheel more efficient. The wooden breast was most common in America. In England and Europe it was common to have a stone breast, extended along the lower curve of the water wheel just beyond its vertical center.

The breast shot water wheel came in three different types: the middle, low and high breast shots. The middle and low breast shot water wheels had deeper buckets to deal with the increased volume of water required for the low head of water to develop power equivalent to that obtained by a high breast shot water wheel. A high breast shot water wheel would then have elbow buckets. A breast shot water wheel combined both the weight and impulse of the water in their operation, and these water wheel were larger in diameter and wider than many other water wheels. They were often well designed wheel that made them very popular with industry.

One of the big differences between that of a breast shot water wheel and that of the overshot and pitch-back is that the breast shot water wheel is much wider. An efficient type of apron would terminate with a step downward of about 6 inches usually about a foot before the lowest point in the run. This would enable the water to be discharged rapidly from the buckets so as not to impede the upward motion of the wheel. In the middle and low breast shot water wheels the buckets are deeper as to deal with the increased volume of water required for the lower head of water to develop power equivalent to that obtained by a high breast shot water wheel. Breast shot water wheels suffer less from the problems of back watering because the wheel is turning in the same direction that the water is flowing down the tail race and it tends to push the water way from the wheel as it rotates. Another advantage of the breast shot water wheel operating in back water is that the direction of rotation pushes the floating debris away from the water wheel and not damage the wheel.

Construction of an apron for a breast shot water wheel.

The undershot water wheel is used on falls with very low head, where there may be only a slight fall to a stream. The wheels are found usually with less than 4 feet or with no head at all. These water wheels are moved entirely by the impulse of the water and consequently required much greater quantities of water to produce the same power as developed by the overshot, pitch-back and breast shot water wheels.

They are mainly found on tidal mills and boat or floating mills. The simple form of the water wheel is that of a paddle wheel. They may only be placed were they dip into the current and relay mainly on the movement of the water than by any fall. The weight of the water is not applied. The undershot water wheels usually have no sole or shrouding. Of the three types of vertical water wheels, the undershot is the least efficient and the power developed being comparatively small to that of the size of the wheel and the amount of water that moves it.

In order to make the undershot water wheel more efficient, a portion of the periphery of the wheel from the point of impact of the water to a point below the center of the wheel is surrounded by a casing or dip called an arch. The inside of the wheel should be in cased by a sole or drum boards and the sides shrouded around the periphery. A gate or fore bay should direct the water to the wheel. Undershot water wheels are designed open so if the river or the tide rises on the wheel, the water wheels is open enough so it will simply stop turning and will not be damaged by the rising water. Pitch-back, breast shot and undershot water wheels do not have the nostalgic romance that a turning overshot water wheels have, they simply fill the air with a spray of water droplets as they rotate.

The velocity of the periphery of an undershot water wheel is usually from 500 to 600 feet a minute and that of the breast shot or overshot water wheel is 300 to 450 feet per minute. Generally the larger the diameter that the water wheel is constructed the slower the slower the water wheel will rotate. A wooden water wheel will only turn so fast before it tares itself apart. The overshot water wheel is usually not suitable for heads less than 8 feet or beyond 40 to 45 feet. The size and great weight involved may prelude them from being built as a rule beyond a given limit. This does not mean that there were not water wheels much larger. There was a wheel in Great Britain, at Greenock, 70 feet 2 inches in diameter by 13 feet wide, with 160 buckets, having a depth of 17 inches. The fall of this wheel was 66 feet, and it used 2,266 cubic feet of water per minute thus producing somewhere around 200 horse power.

The construction of these type of water wheels differed little from that of other wheels except that the buckets were replaced by radial floats. The early undershot water wheels usually hand floats constructed of flat boards with no right angles or sole boards on the inside rim of the wheel. Some in later years were encased for increased efficiency by having these backs fitted to prevent the water from shooting over the floats. Some undershot water wheels the floats are fitted into slots in deep shrouds or rims and others the rims are not so deep but were thicker timber that was mortised and had short protruding arms or starts driven into them so the floats could be fastened such as in a flutter wheel. Often from the gate or shut of the undershot water wheels the water flows or moves downward path to strike the floats by an enclosed channel or ramp. The lower the water is channeled to the undershot the further forward of the vertical center the ramp extends beyond the water wheel. But the higher the water leaves the gate and the steeper the ramp the farther behind the vertical center the ramp changes direction and then levels off and extends outward from the water wheel. These channels or ramps were often built of stone or wood. They were close fitting aprons but generally not the tight fitting curve that the pitch-back or breast shot had. The undershot water wheels were built from about 10 to 25 feet in diameter. The floats were from 14 to 16 inches apart at the circumference of the wheel and about 12 to 28 inches in depth.

The buckets of these type of water wheels are either straight or flat, curved or have "kneel buckets" or elbow buckets. The curved are generally iron or steel. The kneel or elbow buckets and flat buckets are constructed on wooden water wheels. The curved buckets are made to retain water to its lowest point as possible and in many respects are superior to that of the elbow bucket. The power may be taken off by a torsion, that is a pulley or gear mounted to the axle of the shaft or bolted in segments to the arms of the water wheel near the periphery, by means of a pinion engaging the teeth of the water wheel. Originally the gear was attached to the segmental sections of the shrouding or rim of the water wheel. But because of the problems in keeping a wooden water wheel balanced and in proper "round," the gear was then placed on the arms of the water wheel. This was more effective on the down going side than on the ascending side.

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Copyright 2000 by T. R. Hazen