Hydrodynamic Brake

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Hydrodynamic braking, also known as retarding, is an alternative way of slowing down a motorized rail vehicle, without wearing and overheating the brake shoes. It is a dynamic braking feature of vehicles using fluid couplings or torque converters as part of their transmission, namely those of diesel-mechanical and diesel-hydraulic type.

To make the hydrodynamic brake operational, the driver needs to disengage the throttle and have the reverser set to the direction the vehicle is moving. The brake is typically operated by a lever that controls the amount of hydraulic fluid inside of the coupling, inducing extra friction to the fluid inside, as needed. This slows the vehicle down at the cost of heating up the fluid.

Hydrodynamic braking, featured only on some motorized vehicles, does not provide a very powerful braking force for large trains, but it can slow them down over time if used tactfully. The effect of hydrodynamic braking is the highest at high speeds. The lower the speed, the weaker the braking force. At low enough speeds it practically has no effect. To bring a vehicle to a complete stop, the driver must use braking methods that rely on brake shoes.

The driver needs to disengage the hydrodynamic brake before being able to operate the throttle and reverser again.