An American Engineer Lester A. Pelton discovered this (Fig. 3.1) turbine in 1880. It operates under very high heads (up to 1800 m.) and requires comparatively less quantity of water.

It is a pure impulse turbine in which a jet of fluid delivered is by the nozzle at a high velocity on the buckets. These buckets are fixed on the periphery of a circular wheel (also known as runner), which is generally mounted on a horizontal shaft.

The primary feature of the impulse turbine with respect to fluid mechanics is the power production as the jet is deflected by the moving vane(s).

The impact of water on the buckets causes the runner to rotate and thus develops mechanical energy. The buckets deflect the jet through an angle of about 160 and 1658 in the same plane as the jet.

After doing work on the buckets water is discharged in the tailrace, and the whole energy transfer from nozzle outlet to tailrace takes place at constant pressure.

The buckets are so shaped that water enters tangentially in the middle and discharges backward and flows again tangentially in both the directions to avoid thrust on the wheel. The casing of a Pelton wheel does not perform any hydraulic function.

But it is necessary to safeguard the runner against accident and also to prevent the splashing water and lead the water to the tailrace.

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