Difference Between Impulse and Reaction Turbine

Published: 19 Jul 2025

Hydraulic turbines help turn water energy into usable mechanical power. Depending on the location, this water energy may have more pressure or speed. So, it’s important to choose the right turbine. Turbines are mainly divided into two types: impulse turbines and reaction turbines. The difference lies in how they handle the pressure and velocity to spin the turbine.

Impulse Turbine

It converts all the water pressure into kinetic energy using a nozzle before it hits the turbine.
It works at atmospheric pressure. There is no change in the pressure inside the turbine.
Blades are only active when a water jet hits them.
Water hits the blades directly at high speed from a nozzle.
The runner blades are hit by water jets only from one side.
The runner (rotating part) doesn’t run full of water; air can freely enter.
The outer casing only prevents water from splashing. It does not affect turbine performance.
Usually installed above the tailrace (water outlet).
Water flow can be easily controlled without reducing energy.
Water moves over the blades at nearly the same speed or slows slightly.
It is easy to install and maintain because of its simple design.
No special sealing is needed since it operates in open air.
Flow can be changed easily using valves—no energy loss.
Ideal for high-head, low-flow areas like the mountains.
Common types include: Pelton wheel, Turgo, Banki turbine.

Reaction Turbine

It converts only part of the water pressure into kinetic energy; the rest is used within the turbine blades.
It works with pressure. Pressure drops as water moves through the blades.
Blades are always under water pressure and work continuously.
Water flows around and over the blades, staying in contact longer.
Blades are surrounded by flowing water, with pressure on both sides.
The runner is always full of water; no air contact.
The casing is essential to maintaining pressure and controlling flow.
Ideally, it should be placed below the tailrace and always remain underwater.
Flow control causes energy loss, making regulation less efficient.
Water loses both pressure and speed as it moves through the blades.
It has a more complicated design and needs careful setup and regular checkups.
Needs air-tight sealing to handle pressure inside the casing.
Changing the flow affects pressure and causes energy loss.
Best for low-head, high-flow areas like rivers.
Common types include Francis, Kaplan, and propeller turbines.

Conclusion

In both cases, impulse and reaction turbines help turn water energy into useful power. Impulse turbines are best for high-head sites with simpler setup needs, while reaction turbines suit low-head applications where constant pressure and flow matter more. By understanding the differences between these turbines, engineers can make the right choice for efficient hydroelectric performance.