How 18 Wheeler Air Brakes Work

Semi Truck

Anyone that has ever driven a commercial truck, bus, trailer, or semi-trailer understands that air brakes are often utilized. This is often for a very specific reason, as the nature of an air brake system allows for increased reliability and efficiency.

 

The major advantage is that air is an infinite resource and will never run out; because of this, with a leak the system is still functional and does not need to be replenished. Additionally, research will also show that air brakes also allow multiple vehicles to be coupled. Thus, when all of the units must break, it can also mean that this can be controlled from inside the cab.

 

Heavy trucks are also notable for using a dual air brake system, which is comprised of two air brake systems combined, yet only has one set of brake controls. This allows for the ability to retain braking, even if one of the systems fails. Additionally, there is also the ability to ensure a steady supply of compressed air, and as mentioned, this ensures that the braking system will continue to be operational; no matter what.

 

All of these measures work to ensure that safety is maintained. As one can imagine, when operating a heavy vehicle, braking can often mean that one is spared from an accident, which not only affects the driver of the heavy vehicle, but also other drivers on the roadway as well.

 

One should also be aware of the three types of brakes:

 

  • Service Brakes: Not only are service brakes activated when they are supplied with air, but they are activated whenever the driver pushes down on the brake pedal. Once the air is pushed through the brake chamber, a pushrod is forced out, which then pushes a slack adjuster. This then turns the camshaft, which twists the S-Cam and forces the brake lining to make contact with the brake drum. Due to the friction, the vehicle is then forcibly slowed.

 

  • Spring Brakes: These brakes are typically utilized in order to meet parking and emergency brake standards. While driving, springs are held back by a great deal of air pressure. When pressure is then removed, the springs put on the brakes. Remember, it is important to know that these brakes are different than service brakes. Generally, when these brakes are released this is done through approximately 60 psi.

 

 

  • Emergency Brakes: These brakes are contained with a steady stream of airflow inside the brake chamber. Additionally, this also holds a spring, which is kept restrained by the air system. When this air in the system is not of a viable quantity, the spring, and by default the brakes, will automatically engage. Typically, this is done when there is a drop of a 20-45 psi range.

 

When driving heavy vehicles, it is very important to understand how these mechanisms work in order to ensure that all of the components are working efficiently. When these mechanisms do not correctly, it can not only cause the braking system to work incorrectly, but could also potentially cause accidents in various degrees of severity.

 

Source:

 

http://www.easternmarine.com/tech-info/how-air-brakes-work

http://www.newbiedriver.com/abcsupdates/airbrakes101.htm

 

 

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