Impulse turbines are hydraulic machines in which water, going out of the nozze, hits the wheel blades at the highest speed corresponding to the net fall of the plant.

The wheels turn inside chambers at an atmospheric pressure; their blades take the greatest thrust from the water flow and then deviate it to the exhaust section.

A typical impulse turbine is the Pelton; less known are the TURGO  and the OSSBEGER.

In the latter ones water operates twice on the wheel blades before it reaches the exhaust section.

Pelton turbine rotor