A Kaplan turbine requires a speed ratio of 2.

Kaplan Turbine

Kaplan Turbine: - It is an axial flow reaction turbine in which the flow of water is parallel to the shaft. A Kaplan turbine is used where a large quantity of water is available at a low head.

All parts of the Kaplan turbine such as spiral casing, guide mechanism, and draft tube are similar as in the Francis turbine system except:

The runner: the runner has two major differences. In Francis runner, the water enters radially while in Kaplan type it strikes the blades axially. The number of vanes in Francis turbines is 16 → 24 while in Kaplan it is only 3 → 6 vanes or at most 8 in an exceptional case.

The RPM is more than twice that of the Francis turbine. Kaplan turbines have taken the place of Francis turbines for certain medium-head installations.