Truck Air Brakes
Truck air brakes were invented in the 1870s by a man named George Westinghouse. These brakes are used on larger trucks such as semi-trucks to bring them to a stop when loaded heavily. Typical cars and other smaller vehicles use brakes that work by hydraulics. Hydraulic brake systems use compressed liquid in order to operate. Air brakes use compressed air which is much more powerful, an aspect needed when stopping vehicles that are heavily loaded like tractor and trailers. These trucks can easily weight up to forty tons when loaded and need a much stronger braking system than hydraulics can supply.
Air brake systems typically consist of a control system as well as a supply system. The supply system includes the air compressor which captures air from the atmosphere and then compresses the air. The air is then sent to the air drier which removes any moisture and impurities and then sends the compressed air on through various air valves and lines to tanks for storage until needed. The control system is needed to send the compressed air to the different wheel cylinders which then activates the braking system for each wheel individually. When the brake pedal is applied by the driver, check valves in the system are activated and the compressed air is then sent through the lines to each wheel. This air then enters each of the brake cylinders and is modulated depending on how much pressure is applied to the brake pedal. The harder a driver presses on the brake pedal, the more air is released into the system. When the pedal is released, the compressed air bleeds out from the cylinders and allows the wheels to begin moving once again.
The control system also contains two parts. These are the trailer brake circuit and the parking brake circuit. These two brake circuit systems are also split into different circuits for the front and the rear wheels. The circuits receive the compressed air from different individual reservoirs. This is done for safety reasons just in case the truck driver experiences an air leak. This allows the truck to stop on all wheels that are not affected by the leak. The parking brake is also air operated and works on a spring like application. Trailer brakes also include both the supply line and a separate control or service line. The supply line receives its needed air from a variety of sources while the service or control line helps by controlling the use of the air in the trailer braking system.
Although some disc-type air brakes are now being used on trucks, most air brake systems use drum-type mechanisms in order to operate. The drum brake system includes a hollow drum or chamber. Two brake shoes are located inside each brake drum or chamber. When the brake pedal is pushed, activating the truck air brake system, the air is pushed through the cylinder which rotates a cam. This pushes the two brake shoes against the drum walls and the friction of this action helps to slow and stop the truck. Disc brakes work in much the same way with the difference being that instead of shoes, disc braking systems use brake pads. The friction of the pads against the rotors in the brake system stops the truck.
18-wheeled trucks as well as buses, trailers and other larger vehicles are typically designed with air brake systems. Originally, air brakes were designed to be used on trains and many trains today still use this type of braking system. Air brakes are much more commonly found however on larger and heavier trucks such as those used for the transporting of goods.