Electronically controlled pneumatic brakes

Electronically controlled pneumatic brakes are a type of modern railway braking system which offer improved performance compared to traditional railway air brakes.

Traditional train braking systems use pneumatic valves to control and generate brake applications on the cars along the length of the train. In general, this conventional system consists of a brake pipe that runs the length of the train which supplies air to reservoirs mounted on each of the cars. When the brake pipe and car components are charged with air, the brakes release. When the engineer needs to make a brake application, control valves in the locomotive reduce the brake pipe pressure. As the brake pipe pressure reduces, the service portion on each car divert air from their reservoirs to their brake cylinders. To release the brakes, the engineer charges the brake pipe. This method of controlling the brakes on freight and passenger cars has been virtually the same since its invention by George Westinghouse in 1868.

The conventional braking system suffers from many weaknesses; one of which is in the reaction time. Because the engineer controls the flow of air into and out of the brake pipe from the locomotive, it can take up to two minutes for a commanded brake application to propagate to the back of a long freight train. This uneven braking can cause significant forces to build up between the cars in a train.

Also, since the brake pipe is typically used for control and supply of air to the cars, if an engineer is not careful, the air supply can be depleted. Further, since the engineer is only aware of the brake pipe pressure and flow of air into the brake pipe, it is not easy to know the state of the train brakes at any given time.

In contrast, ECP braking uses electronic controls which make it possible to activate air-powered brakes on the cars. On an ECP-equipped train, the cars are equipped with a Trainline Cable that runs parallel to the brake pipe down the length of the train. This cable is used to supply power to the electronic components installed on the cars. The cable also doubles as a communication medium that allows the locomotive to send commands and receive feedback from the cars and the End of Train.

ECP provides many benefits over the traditional braking system. For example, since all the cars receive the brake command at the same time, the brakes are applied uniformly and instantaneously. This provides much better train control, shortens the stopping distances, and leads to a lower risk of derailment or of coupling breakage.

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Wikipedia