Water Wheel
The function of a water wheel is to power a machine to perform a task. Although we don’t think of it with today’s advanced computers and production systems, the water wheel was one of this country’s first labor-saving devices. The amount of power or energy generated by the wheel is measured and described in horsepower. A unit of horsepower is equivalent to 550 feet power per second. Water wheels of the 19th century could operate at ten to thirty horsepower but most functioned with between fifteen and twenty.
Water wheels were made of wood. For best results they should be kept in constant use. If not, parts would dry and shrink, eventually becoming loose. Northern mill owners often would build wheels into mills—devising crude heating systems to keep it ice-free in winters. Buckets, into which the water was directed, would leak, diminishing the amount of power of the wheel. The wheel was certainly not indestructible under the best of conditions. Over a span of five to ten years, most parts of the wheel would need to be repaired or replaced.
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The wheel was set in motion by water entering its buckets. The flow of water was the most crucial contribution of the entire process. To insure a constant flow, a dam was built as close to the mill site, and wheel, as possible. If the dam was any distance from the wheel, water had to be carried from the dam to the wheel via a canal or flume.
Efficiency of all wheels depended upon the head (the difference in level between water feeding the wheel and that leaving it.) A wheel performing at a site with a great head water would be quite large and use many buckets. For best results, water should leave the wheel quickly. Construction of tailraces were used for this purpose. Tailraces were made of oak, pine, or cypress as these woods would contribute most to a long existence.
Mills of the 19th century generally used three types of wheels. The
overshot wheel
was one that water entered from the top. Its diameter could be as great as sixty feet and its width could be three feet. Buckets were ten to fifteen inches in depth and the head for efficient operation was ten to forty fest. It operated at approximately 65% to 75% efficiency.
The
breast wheel
allowed water to enter at the side just above the shaft. It operated best with an eight to ten foot head and the efficiency level for the breast wheel was 50% to 60%.
The undershot
wheel was commonly found at medium-sized dams of five to eight feet. It functioned with a low head and the bottom of the wheel was always submerged in the stream. A gate was installed at the bottom of the dam to direct a constant flow at the wheel’s vanes. (The undershot had no buckets as there was no need to hold the water for any length of time). The vanes were placed eighteen to twenty-four inches apart. This wheel could operate when water in its reservoir was very low, but at best operated only at 40% efficiency.