Water Power: Building a Pelton Wheel

If you're generating power from a flowing water source with a moderate head, a Pelton wheel is a good choice.

| March/April 1972

Though one of man's oldest prime movers, a water wheel generator is still a fascinating piece of machinery. Perhaps this is because it appears comprehensible at a glance (although an efficient wheel is actually a product of subtle and inconspicuous design refinements), and because it seems to be a way of getting power for nothing. The wheel we describe here, with accompanying technical diagram, was especially designed for this series on harnessing small streams, and will reward a careful craftsman by delivering years of constant service. It's particularly suited for an installation having a moderate head (25' to 60') and relatively small flow (0.45 to 0.75 cubic feet per second). Subsequent installments will describe the construction of wheels suited for lesser heads of water and other varied conditions.

The wheel is an impulse wheel, driven by the impulses produced as water strikes revolving blades or buckets. In a perfectly designed wheel, the water strikes at high speed, exhausts its energy in driving the wheel to which the bucket is attached, and then falls free of the wheel.

Known as a Pelton wheel, this type developed from the "hurdy gurdy", a paddle wheel used in California by the forty-niners. The hurdy-gurdy was a wheel that rotated in a vertical plane, had flat vanes fixed around its circumference, and was driven by the force of water striking the vanes. It was not an efficient machine, but it was simple to construct. Then an engineer named Lester Pelton substituted a cup-shaped, divided bucket for each of the vanes, and by that step added a high degree of efficiency to the wheel's other virtues.

No single wheel will meet all operating requirements, but some will perform under a reasonably wide range of conditions. The following table indicates the r.p.m. and horsepower output that will be delivered by this wheel under given conditions of head and flow. The latter is measured in cubic feet per second:

Head: 25'
- Flow: 0.43; RPM: 350; HP: 1.0

Head: 30'
- Flow: 0.51; RPM: 390; HP: 1.3

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