Heavy Truck Brake Systems

An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers.

 Air brakes are used as an alternative to hydraulic brakes which are used on lighter vehicles such as automobiles. Hydraulic brakes use a liquid (hydraulic fluid) to transfer pressure from the brake pedal to the brake shoe to stop the vehicle. Air brakes are used in heavy commercial vehicles due to their reliability. They have several advantages for large multi-trailer vehicles:

• The supply of air is unlimited, so the brake system can never run out of its operating fluid, as hydraulic brakes can. Minor leaks do not result in brake failures.
• Air line couplings are easier to attach and detach than hydraulic lines; the risk of air getting into hydraulic fluid is eliminated, as is the need to bleed brakes when they are serviced. Air brake circuits on trailers can be easily attached and removed.
• Air not only serves as a fluid for transmission of force, but also stores potential energy as it is compressed, so it can serve to control the force applied; hydraulic fluid is nearly incompressible. Air brake systems include an air tank that stores sufficient energy to stop the vehicle if the compressor fails.
• Air brakes are effective even with considerable leakage, so an air brake system can be designed with sufficient “fail-safe” capacity to stop the vehicle safely even when leaking.
• The compressed air inherent in the system can be used for accessory applications that hydraulics are not appropriate for, such as air hornsand seat adjusters