In Impulse Turbine, steam
completely expands in the nozzle itself. Hence its pressure remains constant on
both ends of the moving blades.
In Reaction Turbine, Fixed
blades act as nozzles. Hence steam expands both in fixed and moving blades
continuously as it passes over them. Thus the pressure drop occurs gradually
and continuously over both the fixed and moving blades.
In Impulse Turbine, Blades
Passage is of constant cross section area, as there is no expansion of steam.
In Reaction Turbine, Blade
passage is of variable cross-sectional area (converging type) due to expansion
of steam.
In Impulse Turbine, As pressure remains constant in moving blades, the
relative velocity of steam passing over the moving blades remains constant
In Reaction Turbine,
Continuous expansion of steam means relative velocity in the moving blades
increases.
In Impulse Turbine, Blades
are of symmetrical profile types :hence,
manufacturing of blade is simple.
In Reaction Turbine, The
blade shapes are of aerofoil and non-symmetrical type; hence manufacturing is
difficult.
In Impulse Turbine, Because
of large pressure drop, the steam speed and the running speed are high.
In Reaction Turbine, Due to
small pressure drop, the steam speed and the running speed are low.
In Impulse Turbine, Because
of large pressure drop in the nozzles, the number of stages are less. The size
of an impulse turbine for power output is comparatively small.
In Reaction Turbine, Because
of small pressure drop in each stage, the number of stages are more for the
same pressure drop. Hence the size of the reaction turbine for the same power
output is large. Reaction turbines are multi-stage turbines only.
Impulse Turbine Occupies less
space per unit power
Reaction Turbine Occupies
more space per unit power
Impulse Turbine is Suitable
for small powers
Reaction Turbine is Suitable
for medium and higher powers.