Pelton, Lester Allen (1829–1918)

US engineer who developed a highly efficient water turbine used to drive both mechanical devices and hydroelectric power turbines using large heads of water. The Pelton wheel remains the only hydraulic turbine of the impulse type in common use today.

From Ohio, Pelton joined the California gold rush at the age of 20. He observed the water wheels used at the mines to power machinery, and came up with improvements. By 1879 he had tested a prototype at the University of California. A patent was granted 1889, and he later sold the rights to the Pelton Water Wheel Company of San Francisco.

The energy to drive these wheels was supplied by powerful jets of water which struck the base of the wheel on hemispherical cups. Pelton's discovery was that the wheel rotated more rapidly, and hence developed more power, with the jet striking at the inside edge of the cups, rather than the centre; he built a wheel with split cups.

By the time of his death, Pelton wheels developing thousands of horsepower in hydroelectric schemes at efficiencies of more than 90% were in operation.