The above figure shows a simple single stage Impulse turbine. It consists of a wheel which is fitted upon turbine shaft. There is only one set of impulse type blades, which are rigidly fixed around the wheel. The steam enters through one set of convergent-divergent nozzle, fitted with the casing at high (inlet) pressure PH and low (inlet) velocity VL. The steam expands in the nozzle and impinges on the blades. As a result, pressure drops to PL with increase in velocity and the wheel rotates. As the steam passes over the blades, the pressure PL remains constant with decrease of velocity. But at exit (VL), it will be still higher than at its entry as shown in the figure below. Hence, there will be considerable loss in kinetic energy.
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