Difference Between Impulse and Reaction Turbine

All the available energy of the fluid is converted
into kinetic energy by an efficient nozzle that forms a
free jet
Only a portion of the fluid energy is transformed
into kinetic energy before the fluid enters the turbine
The jet is unconfined and at atmospheric pressure
throughout the action of water on the runner, and during
its subsequent flow to the tail race.
Water enters the runner with an excess pressure,
and then both the velocity and pressure change as water
passes through the runner
Blades are only in action when they are in front of
the nozzle.
Blades are in action all the time.
Water may be allowed to enter a part or whole of
the wheel circumference
Water is admitted over the circumference of the
The wheel does not run full and air has free access
to the buckets.
Water completely fills the vane passages throughout
the operation of the turbine.
Casing has no hydraulic function to perform; it
only serves to prevent splashing and to guide the water
to the tail race.
Pressure at inlet to the turbine is much higher
than the pressure at outlet ; unit has to be sealed from
atmospheric conditions and, therefore, casing is
absolutely essential
Unit is installed above the tail race.
Unit is kept entirely submerged in water below the
tail race.
Flow regulation is possible without loss.
Flow regulation is always accompanied by
When water glides over the moving blades, its
relative velocity either remains constant or reduces
slightly due to friction.
Since there is continuous drop in pressure during
flow through the blade passages, the relative velocity
does increase.

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