We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Automotive

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is a Vacuum Brake?

By Paul Scott
Updated: May 23, 2024
Views: 8,541
Share

A vacuum brake served as the universal standard braking system on railway trains until it was replaced by the more efficient and safe compressed air systems used today. The vacuum brake system functions by inducing a vacuum in a series of hoses which run throughout the train. These hoses are connected to piston units on each carriage which, when actuated by the vacuum, close brake calipers on the carriage wheels. On older steam trains, the vacuum was supplied by ejectors on the locomotive while newer systems utilized electrically driven vacuum pumps. Although compressed air systems are now the norm on most new trains, there are still rail operators using rolling stock with combination compressed air/vacuum brakes.

Although generally effective, simple vacuum brake systems have one serious, sometimes fatal flaw, i.e., any break in the hoses render the entire system inoperative. This damning "Achilles' heel" led to several serious accidents involving runaway trains and the eventual installation of the safer automatic vacuum brake system. Automatic vacuum systems locked up all of a train's brakes if there was any interruption of the vacuum supply. Although safer, the systems were still slow to initialize especially in the case of long trains. These performance issues slowly led to the widespread installation of compressed air braking systems which are quicker to actuate and release and generally safer.

The vacuum brake system has, at its heart, a central vacuum line or pipe which runs the length of the train. The line is typically a steel pipe on the carriages joined with flexible hoses between the individual carriages. The last carriage has a blank fitting inserted at the end of its vacuum line to close the circuit. On steam locomotives, an ejector supplies the vacuum for the brakes and is regulated by a series of levers in the drivers cab. These ejectors are simple steam operated venturi devices which draw sufficient negative pressure to actuate the vacuum brake system.

When braking force is required, the train driver activates the ejector which draws air out of the central line, thereby creating a vacuum in the system. A braking piston assembly is mounted on the underside of each carriage and connected to the central vacuum line. When moved by the negative pressure in the system, this piston activates a series of linkages which pulls the break shoes up against the carriage wheels. When the brakes are released, the vacuum reduces and air flows back into the piston cylinder moving the it back and reopening the brake caliper to release the wheels.

Share
WikiMotors is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
Share
https://www.wikimotors.org/what-is-a-vacuum-brake.htm
Copy this link
WikiMotors, in your inbox

Our latest articles, guides, and more, delivered daily.

WikiMotors, in your inbox

Our latest articles, guides, and more, delivered daily.