What is a Reaction Turbine – Main Components and Working Principle

What Is A Reaction Turbine?

In this article, we will deeply examine the reaction turbine and the components of reaction turbines. We will also discuss the reaction turbine working principle. it includes in the most famous types of turbine.

reaction turbine

A reaction turbine generates torque in response to the fluid’s pressure and weight. Newton’s third law of motion (actions and reactions are equal and opposite) describes the behavior of RT (reaction turbine). So, a wind turbine includes in its most common types. In the case of a reaction turbine, the water first strikes the fixed blades then strikes the nozzle. While, in impulse turbine (IT), the water first hits the fixed nozzle and then hits the moving blades.

Reaction Turbine Working Principle

The reaction turbine working principle is very simple. That is given below with an example.

reaction turbine

Using a rotor with a moving nozzle and high-pressure water coming out of the nozzle will help us to understand the reaction turbine working principle in a good way. The nozzle receives a reaction force when the water departs the nozzle. This reaction force causes the rotor to spin at high speed.

Similarly, in a reaction turbine working, the reaction force is produced by the moving fluid over the impeller blades. The reaction force generated in the impeller blade causes the impeller to rotate. After driving over the impeller blades, the liquid ends up in the drain and finally in the trail race.


The high velocity with low-pressure water enters into the casing. As soon as it is in the casing, it begins to flow through the guide vanes to the impeller blades. The guide blade guides the water jet and hits the rotor blade at the right angle for maximum performance. The water flowing through the spiral casing has a uniform reduction in cross-sectional area, which means that the volute’s pressure remains constant. These vanes can be tilted to decrease or increase the flow of water to the turbine. If the water flow is fast and the energy requirement is less than that of the blades, the impeller blades are inclined at a smaller angle to the turbine axis so that the impeller blades are also adjustable. When the turbine load is high, and the water flow is low, it is set at a superior angle to the turbine axis.

Two main features that determine the reaction turbine efficiency are the profile of the impeller on which the water slides and the angle of attack when the water hits the impeller blades. Thanks to the adjustability of the impeller and guide vane, the turbine can now be used with different load requirements and water potentials.

The water pressure that emerges after hitting the blade is certainly very low so that the water flows through the guide tube with a uniformly increased cross-sectional area and regains the pressure when it achieves the tailrace. Unfortunately, the pressure differential is too great to recover from the draft tube, which leads to cavitation and corrosion problems.

The velocity diagram of the reaction turbine is given below;

velocity diagram

For betting understanding about a reaction turbine working, watch the below-given video:

Types of Reaction Turbine

There are different types of reaction turbine that are given below.

Types of reaction turbine

1) Propeller Turbines

Main Article: Propeller Turbine

The propeller turbine includes in the famous types of reaction turbine. These turbines usually have a 3 to 6 blade flow path, and the water is in constant contact with all of the blades. Propeller turbines only install at the place where the load and height are constant. Under partial load, this turbine’s energy efficiency curve is very peaked, which means poor performance.

propeller turbine

Kaplan turbines can achieve high-efficiency levels under various load conditions by properly adjusting the blades during their working.

Kaplan turbines allow you to adjust the blade angle or the impeller according to the required power. This allows the Kaplan turbine to work according to the load changes. This is the only reason why Kaplan turbines have full load efficiency and high part load.

However, this is impossible with propeller turbines.

2) Francis Turbines

Main Article: Francis Turbine

This reaction turbine is basically an improved version of the propeller turbine, with the water flowing radially and axially into the runner. In middle section solutions, the flow channels generally set in spiral housing with internally adjustable influence blades.

Francis turbine, reaction turbine

Francis turbine rotor typically has nine or more fixed blades. Water initiates directly above and around the runner, then the waterfalls and turns. The other main components are the draft tube, gate, and spiral in addition to the corridor.

Today, cross-flow turbines are an inexpensive (albeit less efficient) alternative to Francis’s spiral casing machines.

3) Gravity Turbines

Main Article: Turbine

These reaction turbine types convert gravity force into rotational force. So, the gravity turbine converts the kinetic energy of the gravity force into electricity.

gravity turbine

4) Bulb Turbine

This turbine is a variant of a propeller turbine. In these reaction turbine assembly types, the generator is enclosed and sealed in a streamlined watertight steel housing located in the duct center. The generator drives with the help of a variable pitch propeller at the downstream end of the valve.

Bulb turbine

In the bulb turbine, the direction of the water entering and exiting the device is practically unchanged or very little. The compactness of this design gives more flexibility in powerhouse designing.

5) Straflo Turbine

The straflo turbine is an axial turbine. It has fixed blades. These types of reaction turbines have generators outside the water channel. The generator is connected directly to the turbine runner.

Straflo turbine

A tubular Straflo turbine with variable speed uses in the Tidetec turbine design. It is a very famous type of reaction turbine with almost a hundred existing installations.

6) Tube Turbine

In this type of reaction turbine, the pressure line is bent shortly before or after the flow path, enabling a straight connection to the generator.

Tube Turbine

Components of Reaction Turbine 

The reaction turbine components are given below in detail.

reaction turbine components

1) Guide vanes

This reaction turbine component attaches to the spiral casing. The most important function is to ensure that the direction of the water hitting the impeller blades is along the axis of the turbine. Otherwise, the water will create a strong vortex as it passes through the spiral layer. Its rotating impeller blade is ineffective. With modern turbines, the angles of these guide vanes can be adjusted. The water flow can adjust by changing the angle of these guide vanes according to the turbine load.

2) Spiral casing

A volute housing with a uniform reduction in cross-sectional area along the circumference. Because of the small cross-sectional area, there is an opening through which water can flow from the beginning of the casing into the blade. The pressure drops along with the casing, resulting in an even velocity of water hitting the rotor’s paddle. Therefore, the cross-sectional area in the circumferential direction decrease to make the pressure uniform, and the moment and the speed of the impact blades make uniform.

3) Draft tube

The draft tube connects the runner’s exit to the tail run. Because the water exiting the blades is at relatively low pressure, its cross-sectional area increases along its length. Its cross-sectional area continues to expand, which helps relieve pressure as it flows towards the tailrace.

4) Runner or Impeller blades 

It includes in the major reaction turbine components. The shape of the impeller blade is to use the water’s pressure energy to drive the turbine. Its design plays an important role in determining turbine efficiency. Modern turbines allow these blades to tilt around the axis, which allows the pressure of the blades to change depending on the load and available pressure.

Advantages of Reaction Turbine

1) It has high hydraulic efficiency.

2) This type of turbine has a high working speed.

3) It is easy to construct.

4) The blades have high efficiency as compare to the impulse turbine.

5) It requires less space.

6) The reaction turbine uses an oil-free exhaust system.

7) It has a small size.

8) It has a high capability to use high temperature and high pressure.

Disadvantages of Reaction Turbine

1) These turbines require high maintenance as compare to an impulse turbine.

2) Requires high maintenance cost.

3) Thrust force generates in this type of turbine.

4) It faces cavitation problems.

5) It has not symmetrical blades.


1) It uses in hydroelectric power plants.

2) These turbines use in wind power mills for electricity generation.

This article deeply discusses reaction turbine components, reaction turbine working, and some other aspects. I hope that this article will be too much helpful for you. So, feel free and contact me if you have any confusion related to this topic. I will try my best to clear your confusion.

See More:

1) Turbine and Its types

2) Impulse Turbine

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