Water brake

A water brake is a type of fluid coupling used to absorb mechanical energy and usually consists of a turbine or propeller mounted in an enclosure filled with water. As the turbine or propeller turns, mechanical energy is transferred to the water due to turbulence and friction. In this process, the water heats up (to the boiling point).

The amount of resistance can be varied by changing the amount of water in the enclosure. Water brakes are commonly used on some forms of dynamometer.