Pioneered by George Westinghouse in the late 19th century, compressed air brake systems were developed to improve the reliability and safety of rail brakes. Over the years, Westinghouse鈥檚 design has been adapted and upgraded in response to the latest technological advances, but in its essence, it鈥檚 still in nearly universal use today.
Let鈥檚 explore the science behind this critical safety device that protects millions of travelers and commuters on a daily basis:
The Westinghouse braking system is centered around an apparatus called a 鈥渢riple valve鈥�. The name refers to its three primary applications: charging air into tanks to be stored, applying braking when brake line pressure drops, and releasing the brakes after application.
These applications occur in order. Air is constantly pumped (or charged) into air tanks attached to each car. The air is then pumped into the brake line, which toggles a valve that separates the air tank from the brake itself.
When pressure from the brake line to that valve stops, the triple valve automatically reconnects the air tank to the brake, applying the brake in the process. As soon as the air in the tank reaches full pressure again, pressure to the brake line resumes, prompting the system to release the brakes so that the train can move.
Since their invention in the 1800s, compressed air brake systems have benefited from a number of improvements. These developments have made these systems an ideal choice for modern mass transit systems.
In particular, modern compressed air brakes are designed to ensure that they still work automatically even if a leak or a malfunction causes a train to lose some of its compressed air supply. Most systems are now outfitted with an emergency feature that allows quicker application via an extra emergency reservoir.
Similarly, a modern compressed air brake features an AB freight control valve that centralizes piping in the system by bringing the service and emergency pipes together on a single bracket.
To prevent trains from running away after losing pressure, many trains also employ or a two-pipe air brake system, which introduces a new pipe 鈥� the main reservoir pipe, to be continuously charged with air from the train鈥檚 main air tank.
Unlike hydraulic alternatives, which depend on an exhaustible supply of braking fluid, compressed air brake systems run on a constantly regenerated stream of pressurized air. As a result, they鈥檝e long been the golden standard for mass transit systems around the world. After all, a subway can鈥檛 afford to stop en route to replenish its braking fluid.
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