How Do Air Brakes Work?

April 21, 2021

The Rolling Rig

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It takes a lot of power to stop an 80,000-pound vehicle in its tracks, but that’s the magic of air brakes in action. But just what is an air brake and how do they get such stopping power at a moment’s notice? The team at International Used Truck Center is here to give you the basics of how an air brake works, so you can understand just how important they are for your travels in and around . Let’s take a look at one of the most crucial components in your entire vehicle.


Before answering the question “How do air brakes work?,” let us get into the triple-valve system. The triple-valve system performed three functions, thus its name. Let’s take a look at those functions.

  1. Charging: The system must be pressurized with air before the brakes will be released. While the vehicle is at rest, the brakes are engaged. Once the system reaches its operating pressure, the brakes are ready to be deployed.
  2. Applying: As the brakes are applied, air pressure decreases. The valve allows air back into the reservoir tanks, while the brakes are moved to the application position.
  3. Releasing: Once the brakes are applied and the air escapes after braking, the increased pressure releases the brakes.

The triple-valve system is the basic concept of how today’s air brakes work in buses, tractor-trailers, and trains. Let’s switch over and answer “How does an air brake work?”


What is an air brake? In a normal passenger car or light truck, you’ll typically find a hydraulic braking system. These braking systems rely on fluids in motion to generate the power needed to stop. But when you’re dealing with massive vehicles like International Trucks or Freightliners, you need a heavy-duty braking system to get the job done. That’s where air brakes come in. Instead of worrying about low braking fluids or leakages in the line, an air brake system uses air to power its brakes. This system is safer, more practical, and more reliable for a commercial vehicle driving through .


So, how do air brakes work, and why are they so common in commercial trucks? Take a look at how air brakes work below:

  • The driver steps on the brakes and then air flows from the reservoir tank into the brake chamber.
  • This moves a piston downward, which also moves a slack adjuster and attached push rod.
  • The slack adjuster and pushrod set another rod into rotation.
  • The S-cam moves the brake shoes toward the brake, which slows the vehicle.
  • The truck comes to a full stop.

Air brakes can be used on both disc and drum brakes, and thanks to their simple operation, maintenance is simple. This means that commercial drivers get all the benefits of heavy-duty braking power and the convenience of low-maintenance design – which means more time can be spent on and roads!


Whether you have more questions about how air brakes work or if you need to concept of air brakes explained further, visit International Used Truck Center to see what we can do for you. Contact us today with any questions, and we’d be happy to help.

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