Reaction Turbine - Parts, Construction And Working

Reaction Turbine - Parts, Construction And Working

            Hydraulic machines are defined as those machines, which convert either hydraulic energy into mechanical energy or mechanical energy into hydraulic energy. The hydraulic machine, which converts hydraulic energy into mechanical energy is called a turbine. The hydraulic machines which convert the mechanical energy into hydraulic energy are called pumps.
            The basic difference between the turbine and the compressor is that the Turbine expands the fluids while the compressor compresses the fluid during the process.

The radial flow turbine is a turbine in which the water flows in the radial direction. The water may flow radially from outwards to inwards or from inwards to outwards. If the water flows from outwards to inwards through the runner, The turbine is known as the inward radial flow turbine. And if the water flows from inwards to outwards, the turbine is known as an outward radial flow turbine.

            The 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 changing into kinetic energy. Thus the water through the runner is under pressure. The runner is completely enclosed in an air-tight casing and casing and the runner is always full of water.

  • Main parts of a radial flow reaction turbine:-
  1. Casing
  2. Guide mechanism
  3. Runner
  4. Draft-tube
  • Casing:-
          As mentioned above that in the case of reaction turbines, casing and runner are always full of water. The water from the penstocks enters the casing which is of spiral shape in which the area of cross-section of the casing goes on decreasing gradually. The casing completely surrounded the runner of the turbine. The water may enter the runner at constant velocity throughout the circumference of the runner. The casing is made of concrete, cast steel, or plate steel.

  • 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 the inlet. Also by a suitable arrangement, The width between two adjacent vanes of the guide mechanism can be altered so that the amount of water striking the runner can be varied.

  • Runner:-
           It is a circular wheel on which a series of radial curved vanes are fixed. The surface of the vanes is 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 stainless steel. They are keyed to the shaft.

  • Draft tube:-

                 The pressure at the exit of the runner of a reaction turbine is generally less than atmospheric pressure. The water at the exit cannot be directly discharged to the tailrace. A tube or pipe of the gradually increasing area is used for discharging water from the exit of the turbine to the tailrace. This tube is an increasing area is called the draft tube.

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