Impulse Turbine

Reaction Turbine

At the inlet only kinetic energy is available. I.e. only momentum transfer.

At the inlet, both kinetic and pressure energy are available.

Steam expands in the fixed blade (which act as a nozzle) itself. The entire pressure drop occurs at nozzles. Therefore, pressure remains constant while it passes over the blades.

The steam expands continuously in both fixed and the moving blades as it passed above them. Thus, the pressure drop occurs in a gradual way during flow over both blades.

Water casing is not necessary.

Air-tight casing is necessary.

Pressure is same at both end of moving blade and is equal to atmospheric pressure.

Inlet pressure is higher than outlet pressure.

In impulse turbine, flow area of moving blade is constant, since there is no expansion of steam.

In reaction turbine, the moving blade do have change in flow area (convergent type).They are shaped like nozzle and accelerate the steam.

Blades are symmetrical about plane of turbine shaft. Therefore, the manufacturing of blade is simple

Blades are asymmetrical.

In impulse turbine, due to great pressure drop, the operating speed is very high.

In the reaction, small pressure drop due to turbine, the operating is low.

Due to high pressure drop on the nozzles, the number of stages are less. The size of an impulse for the power output turbine is comparatively small.

Due to the small pressure drop at each stage, the number of stages are more for the same pressure drop as in impulse turbine. Therefore the size of the reaction for the same output power turbine is large. Reaction turbines are only multi-stage turbines.

Operate at high water head.

Operate at low water head.

Less space per unit power

More space takes per unit power

Turbine Impulse is suitable for small powers generation. More hydraulic efficiency

Reaction turbine is suitable for medium and higher powers generation.

Examples: Pelton wheel, Banki turbine

Examples: Kaplan turbine, Francis turbine, Fourneyron turbine.