The two most basic and fundamental types of steam turbines are the impulse turbine and the impulse reaction turbine.

The Impulse Turbine:

The impulse turbine consists of a set of stationary blades followed by a set of rotor blades which rotate to produce the rotary power. The high pressure steam flows through the fixed blades, which are nothing but nozzles, and undergo a decrease in pressure energy, which is converted to kinetic energy to give the steam high velocity levels. This high velocity steam strikes the moving blades or rotor and causes them to rotate. The fixed blades do not completely convert all the pressure energy of the steam to kinetic energy, hence there is some residual pressure energy associated with the steam on exit. Therefore the efficiency of this turbine is very limited as compared to the next turbine we are going to review- the reaction turbine or impulse reaction turbine.

The Reaction Turbine:

The reaction turbine is a turbine that makes use of both the impulse and the reaction of the steam to produce the rotary effect on the rotors. The moving blades or the rotors here are also nozzle shaped (They are aerodynamically designed for this) and hence there is a drop in pressure while moving through the rotor as well. Therefore in this turbine the pressure drops occur not only in the fixed blades, but a further pressure drop occurs in the rotor stage as well. This is the reason why this turbine is more efficient as the exit pressure of the steam is lesser, and the conversion is more. The velocity drop between the fixed blades and moving blades is almost zero, and the main velocity drop occurs only in the rotor stage.