IMPULSE – REACTION TURBINE

 This utilizes principle of both impulse and reaction. 

IMPULSE – REACTION TURBINE

 • There are a no. of moving blade rows attached to the rotor and equal no. of fixed blades attached to the casing.

 • While passing through the first row of fixed blades, steam undergoes a small drop in pressure and hence its velocity increases a bit.

 • Then it enters the first row of moving blades and like impulse turbine, 26 suffers a change in direction and momentum. This momentum gives rise to impulse on blades.

 • Additionally there is also a drop in pressure while passing through the moving blades which results in an increase in kinetic energy of steam. This kinetic energy gives rise to reaction in the direction opposite to that of the added velocity.

 • Thus the gross driving force is the vector sum of impulse and reaction forces. This turbine is also known as Reaction turbine

DIFFERENCE BETWEEN IMPULSE AND REACTION TURBINE

 S.No. Impulse Turbine Reaction Turbine 

1 Pressure drops only in nozzles Pressure drops in fixed blades (nozzles) as well as moving blades 2

 Constant blade channel area Varying blade channel area (converging type) 

3 Profile type blade Aerofoil type blade 29

 4 Not all round or complete admission of steam All round or complete admission of steam 

5 Diaphragm contains the nozzles Fixed blades similar to moving blades attached to casing serve as nozzle and guide the steam 

6 Occupies less space for same power Occupies more space for same power 

7 Lesser efficiency Higher efficiency

 8 Blade manufacturing is not difficult and thus not costly Blade manufacturing process is difficult compared to impulse and hence costly 

9 Velocity of steam is higher Reduced velocity of steam 

S.No. Impulse Turbine Reaction Turbine

 1 Pressure drops only in nozzles Pressure drops in fixed blades (nozzles) as well as moving blades

 2 Constant blade channel area Varying blade channel area (converging type)

 3 Profile type blade Aerofoil type blade 29

 4 Not all round or complete admission of steam All round or complete admission of steam

 5 Diaphragm contains the nozzles Fixed blades similar to moving blades attached to casing serve as nozzle and guide the steam 

6 Occupies less space for same power Occupies more space for same power 

7 Lesser efficiency Higher efficiency 

8 Blade manufacturing is not difficult and thus not costly Blade manufacturing process is difficult compared to impulse and hence costly 

9 Velocity of steam is higher Reduced velocity of steam