How Does Truck Brake System Work?

Out of all of the pieces of equipment on a car or truck &#; including the steering wheel, engine, and wheels &#; probably the most important when it comes to preventing a crash in Philadelphia is the braking system. This is especially prevalent on trucks or tractor trailers, which are far heavier than normal cars, weighing more than ten times that of a normal passenger car even when empty. This additional weight makes it more difficult for the truck driver to slow the truck down or bring it to a stop in order to avoid a truck accident. These accidents, unfortunately, are far more dangerous for the cars that get hit than they are for the truck that hits them: According to the Insurance Institute for Highway Safety, 97% of the fatalities in truck accidents involving a large truck and a car happened in the car.

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This makes the truck&#;s braking system all the more important.

A Truck&#;s Braking System

Technically, trucks and tractor trailers have three distinct braking systems: The service brake, the parking brake, and the emergency brake. The parking brake and the emergency brake, however, utilize the same equipment, with the only difference being when they are activated.

Here is how each one works.

The Service Brake

A truck&#;s service braking system is the one that a truck driver uses the most often, by far. Just like in a regular passenger vehicle, a truck&#;s service brake is activated by pressing the brake pedal located next to the accelerator, under the vehicle&#;s dashboard and its steering column.

However, many of the other aspects of a truck&#;s service brake system is much different than in a regular car.

The main difference is that a car&#;s service brakes are hydraulic brakes, while a truck&#;s service brake system is an air brake. Therefore, a car&#;s brake utilizes braking fluid and needs a healthy supply of it in the car&#;s brake lines in order to bring the car to a stop. A truck&#;s service brakes, on the other hand, uses pressurized air. This difference has both pros and cons for a truck and those depending on its ability to stop.

The air brake system that most trucks use takes pressurized air from the pistons of the truck&#;s engine compartment and runs it through the air lines that lace the undercarriage of the truck, bringing that pressurized air to the braking system in each wheel. When the pressurized air gets there, it starts a mechanical chain reaction that ends with the brake pads being applied to the rotating wheel, bringing the wheel, and therefore the truck, to a stop. The particular details of the mechanical chain reaction depend on which type of brake the truck uses on its wheels. While there are a handful of types of brakes, the two most common are the disc brake and the drum brake.

A truck that uses disc brakes sends pressurized air through the brake lines to the wheels. The inside of these wheels is attached to a rotor, which spins when the truck accelerates, making the wheel turn and the truck speed up. On opposite sides of the outside of the rotor, a caliper holds the brake pads in place. This caliper gets activated by the pressurized air from the engine compartment when the truck driver hits the brake pedal, squeezing the brake pads to the rotor and slowing both it and the attached wheel.

The other common kind of service brake that trucks use in the U.S. is a drum brake. This makes use of a brake drum, which is shaped like a flat rim that is attached to each one of the truck&#;s wheels. This brake drum includes another flat rim, called the brake shoe. When the pressurized air from the truck&#;s engine compartment enters the drum brake, it pushes the brake shoe outwards, until it comes into contact with the inside surface of the brake drum. Because the brake drum is attached to the truck&#;s wheel, this contact slows the rotation of both the brake drum and the wheel, too, slowing the truck down.

Importantly, these truck braking systems all utilize pressurized air, rather than braking fluid. While this means the braking systems never run out of braking fluid, like a car&#;s braking system can, it also means that there is a small delay from the time of the trucker hits the brakes to when the brakes begin to work. However, this delay is little more than a fraction of a second.

The Parking Brake

In addition to the service brake, a truck comes with a parking brake, as well. Much like in a regular car, this is a spring brake that is activated by pulling a lever in the truck&#;s cab. Its main purpose is to provide a means of preventing the truck from moving while the engine is off.

The Emergency Brake

Finally, a truck is equipped with an emergency brake that is far stronger than its service brake, but which can cause the trucker to lose control of their vehicle and cause a jackknife or rollover accident. The emergency brake is typically the same thing as the parking brake but activated when the truck is in motion.

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Unfortunately, each and every one of these kinds of truck braking systems can wear out. When they do, it can put both the trucker and everyone else on the road in significant danger of a truck accident. These accidents tend to be far more serious for the other people on the highway: The size and height of a truck results in more force and significantly more damage being inflicted on the cars that have the misfortune to be involved in a truck crash.

Understanding Air Brake Systems: Enhancing Vehicle Safety

When drivers are transporting tens of thousands of pounds of weight in a diesel truck, one of the most important components of that vehicle is the brakes.

In big diesel trucks, buses and tractor-trailers, the braking system consists of air brakes. Since air is plentiful but hydraulic brake fluid could get lost in a leak, big vehicles rely on air-powered brakes to keep drivers and everyone else on the road safe.

Air brakes are a critical component of diesel vehicles, such as trucks and buses, and are used to enhance vehicle safety. Diesel technicians need to know how air brakes work and how to troubleshoot, service and maintain air brake systems.

How does an air brake system work? Air brakes work by using compressed air instead of hydraulic fluid to apply the service brakes and release the parking brake. There are multiple air circuits in the system, and the parking brake can also be used as the emergency brake system. Drum brakes and disc brakes, or a combination of both, can be used in air brake systems. The overall functionality and safety of the air brake system rely on the proper maintenance and synchronization of its components.

Keep reading to learn more about different types of brakes, their components and more!

How Truck Air Brakes Work

Air brakes on trucks work using compressed air instead of hydraulic fluid. Air brakes can be either drum brakes or disc brakes, or a combination of both.

Air is pressurized by an engine-mounted compressor. The air compressor then pumps the air into the air storage tanks, which store the compressed air until it&#;s needed.

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Air pressure is used to apply the service brakes and release the parking brake. There are multiple air circuits in the system. The parking brake engages by spring force in the parking brake portion of the spring brake chamber when the air pressure in the chamber is released.

This also allows the parking brake to be used as the emergency brake system. If air pressure was to drop too low, the force exerted by the spring in the chamber will be able to overcome the force exerted by the air on the diaphragm and apply the brakes on all wheels.

You might think of air brakes as working similarly to a hydraulic brake circuit. As with hydraulic brakes, air pressure is applied when the driver presses the brake pedal.

How Drum Brakes Work

Here&#;s how a drum brake operation works.

1. The operator depresses the brake pedal, actuating the air braking system.
2. The air from the reservoirs is supplied for the brake valves.
3. The air from the valves is delivered to the brake chambers.
4. The chambers move the pushrod to push on the slack adjusters.
5. The adjusters transfer pushrod force into cam rotational force.
6. The cam rotates, causing the rollers to rise and force the shoes against the drum.
7. The shoe linings contact the drum to slow or stop the wheel.
8. The operator releases the brake pedal.
9. The delivered air exhausts.
10. The brake shoe return springs force the shoes to release contact from the drum.
11. The brake shoes return to their original positions, causing the cam to rotate back to its original position.
12. The slack adjuster returns to its original position.
13. The brakes are released.

How Disc Brakes Work

For disc brake operation, the process is slightly different.

1. The operator depresses the brake pedal, actuating the air braking system.
2. The air from the reservoirs is supplied to the brake valves.
3. The air from the valves is delivered to the brake chambers.
4. The chamber actuates the caliper, which transfers force to the inner brake pad.
5. The caliper slides on the guide pins as the inner brake pad contacts the brake rotor.
6. A bridge moves with the caliper to move the outer pad against the rotor.
7. The pads squeeze against the rotor, transferring force to stop the wheel.
8. The operator releases the brake pedal.
9. The return spring forces the caliper/bridge back to its rest position.
10. The brake pads separate from the brake disc.
11. The brakes are released.

Components of an Air Brake System

An air brake system in vehicles comprises several essential components working cohesively to ensure safe and efficient braking.

The system includes an air compressor responsible for pressurizing air, which is stored in the reservoir tanks. These tanks store compressed air until needed for braking.

A governor controls the compressor, regulating the air pressure within specified limits. When the brake pedal is depressed, the air pressure releases from the reservoir through a series of valves and hoses, reaching the brake chambers or brake calipers.

The brake chambers convert the air pressure into mechanical force, activating the brake shoes or pads against the drum or rotor, consequently slowing down or stopping the vehicle. A quick-release valve allows for rapid release of air pressure, facilitating swift disengagement of the brakes.

The overall functionality and safety of the air brake system relies on the proper maintenance and synchronization of these parts.

Air Brakes in Different Types of Vehicles

Air brakes in cars

Air brake systems, while commonly associated with larger commercial vehicles like trucks and buses, are not typically found in standard passenger cars. Instead, passenger cars predominantly utilize hydraulic brake systems. These systems operate using brake fluid to transfer force from the brake pedal to the brake pads or shoes, creating friction to slow or stop the vehicle.

Air brakes in buses

When it comes to the safety and functionality of buses, especially those of substantial size and weight, air brakes are extremely important. Buses, like heavy trucks, commonly utilize air brake systems due to their efficiency in managing the significant braking demands posed by these vehicles.

Air brakes in trucks

Integral to the safe operation of trucks, air brakes play a crucial role in managing the substantial weight and stopping power required for these heavy vehicles. Trucks commonly employ air brake systems due to their ability to handle the demanding braking needs imposed by their size and load capacities.

Air brakes in semitrucks

Air brake systems serve as the backbone of safety and control in semitrucks, providing the necessary braking force to manage their immense size and weight. Semitrucks extensively rely on air brake systems, which are vital for ensuring the safety of operation, particularly when navigating highways while hauling heavy loads.

Air Brake FAQs

How do air brakes work in a vehicle?

As discussed earlier, air brakes operate using compressed air to control and facilitate the braking process in heavy vehicles. The system comprises several key components, including an air compressor, reservoir tanks, valves, hoses, brake chambers and brake shoes or pads.

When the driver presses the brake pedal, compressed air stored in the reservoir tanks is released through valves and hoses to the brake chambers. This release of air pressure activates the brakes, causing the brake shoes or pads to engage with the drums or rotors, creating friction and slowing down the vehicle.

What is the purpose of air brakes in trucks?

Air brakes serve a critical purpose in heavy vehicles, such as trucks, buses and large commercial vehicles, by providing reliable and efficient braking mechanisms tailored to handle their substantial weight and demanding braking requirements. Unlike hydraulic systems found in standard passenger cars, air brake systems use compressed air as the medium to transmit force, making them well-suited for heavier vehicles.

Learn How Air Brakes Work Yourself

If that sounds complicated, don&#;t worry. UTI&#;s Diesel Technology program has an entire course on brakes. Students learn how truck brakes operate and the proper service and maintenance of the components.

You don&#;t have to have any prior experience to develop skills in subjects like air brakes at UTI. Many graduates entered the diesel program as complete beginners and left ready to tackle entry-level diesel technician jobs.1

Brian Murphy, Universal Technical Institute (UTI) Education & Development Program Manager, Curriculum, expands on the benefits of enrolling in UTI&#;s Diesel Technology program