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Air Brake

How Air Brake Works

Engineers invented many types of brakes depending upon the need,application and suitability for particular type of vehicle. Though the functions of all brakes are the same, it differs in designn depending on the class of vehicle.

There are different types of brakes, designed for each class of vehicle, such as hydraulic brake, electric brake and vacuum brake. These brake types are sufficient for almost all automobile applications but heavy commercial vehicle needs something more durable and more efficient in order to achieve optimum stopping power. In view of developing something better for heavy vehicles, air brakes came into play, which was designed by the American entrepreneur and engineer “George Westinghouse” in 1869. He also applied for the patent for the design. The air brake found its first application in railways and has been used in many other applications since then.

Construction and Working of the Air Brake

An Air brake is also called a “Pneumatic brake” because it uses air as a the working medium. An Air brake system consists of components such as a compressor, governor, trader valve, pressure regulator valve, sensor, dryer, air or pneumatic lines, air reservoir tank and a brake mechanism.

Air from the atmosphere is drawn inside the air line through the compressor where it is compressed to increase pressure. The Compressor takes power from the engine by suitable arrangements using belt, gear, pulley or shaft. As the air is compressed, the pressure of air increases. The pressure regulator ensures that the value of air pressure remains controllable. Governor, which is located just after the air compressor is used to control or regulate the maximum and minimum amount of the air that flows in to the system through the compressor. The system is usually designed to work with a maximum air pressure of 120 psi and a minimum air pressure of 90 psi. The Governor ensures that the system works under these per-determined limits. It signals the compressor to work according to the pressure. If air pressure falls, it allows the compressor to take more air in to the system and releases the air from the system in case if the pressure requirement is exceeded.

Air is not allowed to enter directly into the system,:as there is every chance that the atmospheric air, while entering inside, would also bring along dust and dirt particles. If dirt or foreign particles enters in to the system, it may damage all the components and damages the system from working effectively. To avoid such circumstances , many vehicles have air filter separately installed, or vehicles use engine filter to filter the incoming air and ensure that the system receives clean dust free air.

From the air compressor, air flows to the air reservoir tank. As the air is released from the compressor and flows through the air line, moisture content develops due to sudden low pressure drop of air from high pressure. Hence, there is an arrangement to remove this moisture. Moisture removal is highly important because it can corrode many parts and it may also freeze in winter thus it could block the supply line and sometime the entire system, too.

Moisture removal is carried out with the help of air dryer located after the air compressor.The air is first passed to the drier, and is then sent to the reservoir tank for storage.

The Reservoir air tank is made up of three different segments or compartments. The first compartment, called as wet compartment that removes the moisture content from the air if it remains even after the filtering from the air dryer. The second compartment, namely rear wheel primary tank, provides the air supply to the rear wheel brake. The third and last compartment, called as front wheel secondary compartment, provides the air supply to the front wheel brake.

When the driver presses the pedal, it actually opens the trader valve that located under the pedal construction assembly. Trader valve paves the way for airflow to reach at the brake chambers from the reservoir tank. Air brake mechanism, which is located inside the brake drum mechanism actuates with the help of this air. Air then passes through the trader valve and air line ultimately reaches to the slack adjuster. High pressurize air presses the slack adjuster back side causing the cam to rotate in its place.This entire process makes friction pad to move outward with the help of S-cam. The outward expansion of brake pads contacts with the rotating drum and stops it.


  1. Air brake uses air as working medium so, there is no danger of fire as with a hydraulic brake.
  2. It reduces stopping distance.
  3. It gives quick braking response.
  4. It contains no fluid so, it's a cost effective braking system.
  5. It's initial cost is less than hydraulic brake.


  1. Higher maintenance cost involved with this brake.
  2. If there is any moisture content in the air it may damage the system or corrode the parts.
  3. It can become blocked completely and can prevent the brakes from functioning.
  4. Adjuster mechanism requires periodic adjustment and maintenance.
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