Page "Turbine" Paragraph 6

Impulse turbines change the direction of flow of a high velocity fluid or gas jet.

The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy.

There is no pressure change of the fluid or gas in the turbine blades ( the moving blades ), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades ( the nozzles ).

Before reaching the turbine, the fluid's pressure head is changed to velocity head by accelerating the fluid with a nozzle.

Pelton wheels and de Laval turbines use this process exclusively.

Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blading on the rotor.

Newton's second law describes the transfer of energy for impulse turbines.