The type of turbine in which a jet of steam from a fixed nozzle pushes against the rotor blades and impels them forward. The velocity of the steam is about twice as fast as the velocity of the blades. Only turbines utilizing fixed nozzles are classified as impulse turbines.
Steam expands in the nozzles with a decrease in pressure, but an increase in velocity before it strikes the motor blading.
The first stage on impulse turbine often permitted to take more than equal share of the available pressure drop, thereby its advantages are:

  1. casing ss subjected to lower striking pressure.
  2. rotational losses is lowered due to decreased steam density.
  3. fitted with high pressure seal.
    Speed of impulse blades rated varies as one half of the steam speed. It permit use of partial admission of steam, on steam chest fitted with nozzle to increase efficient operation.
    Impulse blade are generally attached directly to the wheels, made in longer length attached. Impulse blading is heavier and stronger than reaction turbine.

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