Compressed air brake systems have withstood the test of time for a century and a half. Thanks to performance and safety improvements, they remain the top choice for mass transit. 


Whether they’re driven by a conductor or autonomously operated, streetcars, subway trains, monorails, and AGT vehicles alike all harness the power of compressed air to power their braking systems.

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’s design has been adapted and upgraded in response to the latest technological advances, but in its essence, it’s still in nearly universal use today.

Let’s explore the science behind this critical safety device that protects millions of travelers and commuters on a daily basis:

Mechanics of an Air Brake System

The Westinghouse braking system is centered around an apparatus called a “triple valve”. 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. 

Improved Performance and Safety

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 dynamic braking or a two-pipe air brake system, which introduces a new pipe — the main reservoir pipe, to be continuously charged with air from the train’s main air tank.

Steering Mass Transit

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’ve long been the golden standard for mass transit systems around the world. After all, a subway can’t afford to stop en route to replenish its braking fluid.

At Mattei, we’ve developed a line of rotary vane compressors that are perfectly suited for OEM transit applications. Designed for quality, reliability, and durability, our compressors produce air that meets ISO purity standards while operating more quietly than screw compressors. Thanks to the superior engineering behind them, they’re compatible with every major operating system and motor, including oil-dynamic, electric, power take-offs, endothermic motors, AC and DC motors, and hydraulic motors.

If you’re looking for an air compressor to power your braking systems, Mattei Transit Engineering (MTE) can offer you a full line of custom-engineered electro-pneumatic test equipment and transit system support packages. Contact us today to learn how we can keep your trains running at peak efficiency.

Topics: Air Compressor, OEM/Transit


Additional Resources

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