The PELTON WHEEL is a turbine designed to generate power from a high-speed jet of water as efficiently as possible. Invented by Lester Pelton in the 1870s, the device operates on the principle of planetary swing-by and is highly efficient. The Pelton Wheel can generate quite a bit of energy from a relatively small amount of water, as long as the water is propelled at a high enough speed. This makes it a High Head Turbine, meaning it depends on a fall of (approximately) more than 20 meters.
According to a 1939 article by W. F. Durand of Stanford University in Mechanical Engineering, Pelton´s invention started from an accidental observation, some time in the 1870s. Pelton was watching a spinning water turbine when the key holding its wheel onto its shaft slipped, causing it to become misaligned. Instead of the jet hitting the cups in their middle, the slippage made it hit near the edge (drawing); rather than the water flow being stopped, it was now deflected into a half-circle, coming out again with reversed direction. Surprisingly, the turbine now moved faster.
-- David P. Stern, Planetary Swing-by and the Pelton Turbine
Again, this works because of Planetary Swing-by. Without getting too technical here, it is best to simply say that the water splashing into the middle of the cup wasted energy. Pelton's final design (in the 1870s) used a dual-cup scoop, with a sharp wedge between them, thus preventing the energy-wasting splash effect. He acquired a patent in 1880, and attempted to sell his improved turbines. He had no luck until 1883, where his wheel won a competition held by the Idaho Mining Company of Grass Valley, located in Yuba County, California. They needed a more powerful turbine design for placer mining, and Pelton's turbine was found to be 90.2% efficient (the nearest runner-up came in at only 76.5%,) becoming the wheel of choice. After that, sales boomed, and the Pelton Water Wheel Company was formed in San Francisco.
The largest Pelton Wheel ever built measured 30 feet in diameter, and is on display in Grass Valley. A 15 ton wheel coupled to a generator supplied 18,000 horsepower of electricity to Nevada City for over 60 years. Wheels of all sizes were used all over the country (and ultimately the world) to power devices from sewing machines to entire cities.
There is a monument to the Pelton Wheel in Camptonville, California, where Pelton supposedly invented his wheel in 1878. Rumors of the peculiar design of the wheel's divided cups being inspired by the shape of a cow's nose would appear to be unfounded, but are popular in any case.
Update October 6, 2003: While lost in Nevada City, CA and looking for the freeway exit, I came upon the Pelton Wheel and Five-Stamp Mill which lies at the southeast end of Main St., next to the chamber of commerce. The wheel weighs 15 tons. It was built in 1893 and used (with the accompanying mill, or one like it) to crush gold ore at the Fortuna Mine. It then went on to generate 18,000 horsepower (at a mere 257rpm) for Pacific Gas & Electric from 1928 to 1987 for the purpose of the generation of electricity, and was then donated by PG&E to Nevada City on the occasion of the USA's contitutional bicentennial.
- Webpage: Stern, David P. Planetary Swing-by and the Pelton Turbine. (http://www-istp.gsfc.nasa.gov/stargaze/Spelton.htm)
- Website: Malakoff & Co. Coins &c., The California Gold Country: Highway 49 Revisited (http://malakoff.com/goldcountry/index.htm)
- Webpage: California Online Highways, Pelton Wheel and Five-Stamp Mill. (http://www.caohwy.com/p/peltonw5.htm)