The turbine, which was named after James Francis, was developed and improved upon by him in the USA. Francis invented the guide vane mechanism. Francis turbines are the most widely distributed, as they are universally applicable.
With the Francis turbine, water spins through a spiral-shaped tube. After this, the water is aimed over the guide blades and manoeuvred onto the moving wheel inside. Through the pressure of the water, the rotor wheel is placed in motion. With the help of the guide blade, the rotational speed and the output of the turbine can be controlled. When the water has passed the turbine rotor, it flows downwards and away. The Francis turbine is suitable for medium drop heights from 50m to 700m and medium flow rates. It is therefore implemented in run-of-river power plants and in storage power plants.