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 Servo?

By Jeremy Laukkonen
Updated: May 23, 2024
Views: 12,018
Share

Vacuum servos are devices that are used in many cars and trucks to reduce the effort required to activate the brakes. This component, which is also known as a vacuum brake booster, consists of a large vacuum reservoir that is divided into two compartments. One end of the device is connected by linkage to a brake pedal and the other end consists of a plunger that is in contact with the brake master cylinder. When the driver depresses the brake pedal, atmosphere enters one of the compartments in the reservoir. This pressure differential magnifies the force that was applied via the brake pedal, so less effort is required from the driver than would be if the vehicle lacked a vacuum servo.

Internal combustion engines generate vacuum as a natural part of the combustion process. This is typically referred to as manifold vacuum, and it may be used to power components such as windshield wiper motors and vacuum bake boosters. Vehicles that use diesel or electrical motors may also use a vacuum servo by utilizing a component known as a vacuum pump. These devices are either mechanically or electrically powered and work by pumping the air out of a sealed container.

Early automotive braking systems used direct, mechanical connections between brake pedals and master cylinders. This type of system uses only the force available from the driver's foot to depress the master cylinder to activate the brakes. As a result, a great amount of force is often required and it may take some time for pressure to build up and the brakes to activate. A vacuum servo not only reduces the effort required to activate the master cylinder, but also typically provides full braking power as soon as the pedal has been depressed a certain distance.

Vacuum brake boosters operate by creating and then exploiting a pressure differential. A typical vacuum servo consists of two sealed vessels, one inside the other. Vacuum is applied to remove air from inside both containers, and a check valve typically keeps atmosphere from accidentally reentering.

Typical vacuum servo designs also include a diaphragm between the two sealed vessels. Air is allowed to enter one of the chambers as the brake pedal moves downwards, which create a pressure differential and moves the diaphragm. Additional air can enter the device as long as the pedal is depressed, creating a larger pressure differential and more braking force.

Some vehicles, particularly large combination trucks, use air brakes that do not require a vacuum servo. Other vehicles use a hydraulic brake booster, regardless of whether vacuum is readily available. One particular application uses the same pressurized fluid to operate the power steering rack and provide a boosting force to the brakes.

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
By anon287351 — On Aug 25, 2012

In a vacuum booster, there are holes on the piston plates. Why are the holes drilled in the piston plate?

Share
https://www.wikimotors.org/what-is-a-vacuum-servo.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.