Working principle of Impulse and Reaction Turbine

Are you looking to know about the Working principle of Impulse and Reaction turbines?

Then you came to the right place, Here you learn working principles and comparisons between both of the turbines in a simple and digestible manner.

Surprisingly, you can download this whole article as a pdf and ppt at the end, So don’t forget to take it away with you.

So, let’s get started…

Firstly, I will start with the impulse turbine, so here I go…

Working Principle of Impulse turbine-

The impulse turbine works on the principle of Newton second law, the resulting motive force is due to the change in momentum that gives rotation to the turbine shaft.


In general, When high-velocity fluid is thrown on the rotor moving blade via a fixed nozzle, due to impulse force rotor start to rotate depending on the mass and velocity of the fluid.

impulse turbine

Construction of Impulse Turbine-

Water is stored at the height and pass through a nozzle situated at almost ground level to provide high-velocity transmission of fluid.

When fluid strikes the bucket connected to the runner, it forces the runner to rotate at its own axis by converting the high-speed jet energy into rotational energy to produce electricity through the generator.

Here are some main components used in Impulse turbine-

Spear– To regulate the flow of water according to turbine loads, the spear is moved in and out inside the nozzle.

NozzleTo pressurize the flow of fluid and provide a suitable angle of strike, the fixed nozzle is used in the impulse turbine and it is one of the essential components of this turbine which is usually made of tungsten carbide.

generally, multiple nozzles are used to ensure maximum efficiency because to obtain the maximum efficiency, the flow of fluid should be twice higher than the rotating runner shaft.

Bucket– Bucket is installed at runner shaft, providing bucket-shaped blade facing to the nozzle to absorb the maximum amount of high-energy fluid coming from the nozzle, as you would have seen in the diagram above.

Penstock– Penstock is basically used to drive water from a reservoir or dam in high-speed flow to the turbine and it is usually made of steel.

Casing– Casing is the outer shield of the turbine and it is used to control the water flow and give it direction to go out from the turbine and also to protect the equipment inside the turbine.

RunnerRunner is used to mount the bucket and it is attached to the shaft which further converts water energy into mechanical energy.

TailraceTailrace is the place where used water is exited from there.

This was the construction and working of impulse turbine. Now, I am going to head toward the types or impulse turbine example.

Types of Impulse turbine

Here are some types or examples of the Impulse turbine according to head load in descending order-

  • Pelton
  • Turgo
  • Crossflow
  • Multi-jet Pelton
  • Undershot waterwheel

To know about more of these some of the turbines, Recommend going to Classification of turbines.

Application of Impulse Turbine

Here are some applications of the impulse steam turbine

  • Reverse osmosis plant
  • Supply drinking water
  • Electric power generation

Now, let’s move on to the reaction turbine and further you will learn a comparison between these two turbines. So, here we go…

Working Principle of Reaction turbine-

60% of the hydro-power plants used to efficiently generate electricity through reaction turbine all around the globe. Reaction turbine is those type of turbine which develop torque by reacting to the pressure or weight of the fluid.

Here, the reaction turbine works on the principle of the Newton third law of motion, which state that action will be equal and opposite to reaction, in general.

Reaction turbine are those which operate under hydraulic pressure energy and part of kinetic energy.

In this case, the water reacts with the vanes as it moves through the vanes and transfer its pressure energy to the vanes moves in turn rotating the runner on which they are mounted.

Firstly, water eneters from the penstock and goes to the movable guide vanes and then moves to the fixed guide vanes, which creates the pressure difference in water due to these sets of blades, which is further called reaction force and this force is caused to rotate the runner blades and further turbine.

reaction turbine

Construction of Reaction turbine-

There are many component used in reaction turbine but the main component of this turbine are-

  • Spiral Casing
  • Guide mechanism
  • Runner
  • Draft tube
  • Penstock

Spiral casingThe casing is made with uniformaly decreasing cross-sectional area along the circumference and here due to decreasing cross-sectional area provides the uniform velocity to the water, when water strikes the runner blades and thus this design of casing provides the uniform momentum and uniform velocity to the water to further strike the runner blades.

The material used to manufacture spiral casing is- Concrete and steel.

Guide mechanism– To provide the direction to the water, guide mechanism is used, where Guide mechanism are actually installed inside the spiral casing. Here, the modern turbines are coming with adjustable guide vanes where rate of water flow can be adjusted by varrying the angle of the guide vanes, according to turbine’s load.

Runner– Runner blades uses water’s pressure energy to run the turbine and this runner counts as important component of the reaction turbine. Here, in modern turbines the runner blades can varry pressure force acting on them according to turbine’s loads and available pressure.

Draft tube– It generally connects runner exit to the tail race which have uniformaly increasing cross-section area which further helps to recover the pressure of water.

Penstock– Penstock is usually used to drive water from the water reservoir or dam directly into the turbine.

This was the construction and working of reaction turbine, now lets discuss about example of this turbine.

Examples of Reaction turbine-

There are moslty  two example of this turbine-

  • Francis turbine
  • Kaplan turbine

You can further read about these turbines in Classification of turbine

Application of Reaction Turbine

Here are some application of this turbine-

  • Used in wind power mills to generate electricity.
  • Mostly used in hydro power plants to generate electricity.
  • Only turbine which gives maximum power out from a low available water head & high velocity.

After sharing most of the information of these turbines, let’s head on to the our last headline of this session, So, here we go…

Difference between Impulse turbine and Reaction turbine

Here are 10 major differences between these turbines-

Impulse Turbine Reaction Turbine
Example of an impulse turbine is the pelton turbine Example of a reaction turbine is francis and kaplan turbine
Energy at inlet to moving blade  is only kinetic energy. Energy at inlet to moving blades is kinetic energy and pressure energy.
The entire fluid energy of the water is first converted into kinetic energy in the nozzle. The available energy of the water is partly converted kinetic energy in the fixed blades.
The pressure of the flowing water reamins constant and equal to atmospheric pressure. The pressure and velocity both are changes while passing through runner.
Water flows through the noxxle and strikes on the moving blades mounted on the wheel. The water first enters the fixed blades and then runner.
Water may be admitted over a part of circumference. Water must be admitted over the whole circumference of the wheel.
It is not required that wheel should run inside the water. It is required that wheel should be always inside the water.
It is possible to regulate the flow without loss. It is not possible to regulate the flow without loss.
Governing by needle valve fitted into the nozzle. By the guide mechanism assembly.
The highest efficiency is 80%. The highest efficiency is 95%.

Thats it for now, Hopefully you got the information regarding impulse and reaction turbine and it various aspects, which possibly discussed above.

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