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Reaction Turbine


In the Radial flow turbines water flows in the radial direction. The water may flow
radially from outwards to inwards (i.e. towards the axis of rotation) or from inwards to outwards. If the water flows from outwards to inwards through the runner, the turbine is known as inwards radial flow turbine. And if the water flows from inwards to outwards, the turbine is known as outward radial flow turbine. Reaction turbine means that the water at the inlet of the turbine possesses kinetic energy as well as pressure energy. As the water flows through the runner, a part of pressure energy goes on charging into kinetic energy. Thus the water through the runner is under pressure. The runner is completely enclosed in an air-tight casing and the runner is always full of water.

Main parts of a Radial flow Reaction turbine:

1. Casing
2. Guide mechanism
3. Runner and
4. Draft tube.

1. Casing:

 in case of reaction turbine,
casing and runner are always full of
water. The water from the penstocks
enters the casing which is of spiral shape
in which area of cross-section one of the
casing goes on decreasing gradually.
The casing completely surrounds the
runner of the turbine. The water enters
the runner at constant velocity throughout the circumference of the runner.

2. Guide Mechanism:

 It consists of a stationary circular wheel all around the runner of the
turbine. The stationary guide vanes are fixed on the guide mechanism. The guide vanes allow the water to strike the vanes fixed on the runner without shock at inlet. Also by suitable arrangement, the width between two adjacent vanes of guide mechanism can be altered so that the amount of water striking the runner can be varied.

3. Runner:

 It is a circular wheel on which a series of radial curved vanes are fixed. The
surfaces of the vanes are made very smooth. The radial curved vanes are so shaped that the water enters and leaves the runner without shock. The runners are made of cast steel, cast iron or stain less steel. They are keyed to the shaft.

4. Draft - Tube: 

The pressure at the exit of the runner of a reaction turbine is generally less
than atmospheric pressure. The water at exit can‟t be directly discharged to the tail race. A tube or pipe of gradually increasing area is used for discharging the water from the exit of the turbine to the tail race. This tube of increasing area is called draft-tube.
Inward Radial Flow Turbine: In the inward radial flow turbine, in which case the water from the casing enters the stationary guiding wheel. The guiding wheel consists of guide vanes which direct the water to enter the runner which consists of moving vanes. The water flows over the moving vanes in the inward radial direction and is discharged at the innerdiameter of the runner. The outer diameter of the runner is the inlet and the inner diameter is
the outlet.

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