Air brakes are used in commercial vehicles, which require a heavier braking effort than that can be applied by the driverâ„¢s foot. The following layout shows the arrangement of the air braking systems in heavy vehicles.Compressed air from compressor passes through the unloader valve and maintains its pressure. This air is stored in the reservoir. From the reservoir it goes to the Brake Chambers through many brake valves. In the brake chamber this pneumatic force is converted into the mechanical force and then it is converted into the rotational torque by the slack adjuster, which is connected to S-cam. This torque applies air brakes.

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COMPONENTS OF AN AIR BRAKE SYSTEM:
Air brake system consists of the following components:
Compressor:
The compressor generates the compressed air for the whole system.
Reservoir:
The compressed air from the compressor is stored in the reservoir.
Unloader Valve:
This maintains pressure in the reservoir at 8bar.When the pressure goes above 8 bar it immediately releases the pressurized air to bring the system to 8-bar pressure.
Air Dryer:
This removes the moisture from the atmospheric air and prevents corrosion of the reservoir.
System Protection Valve:
This valve takes care of the whole system. Air from the compressor is given to various channels only through this valve. This valve operates only at 4-bar pressure and once the system pressure goes below 4-bar valve immediately becomes inactive and applies the parking brake to ensure safety.
Dual Brake Valve:
When the driver applies brakes, depending upon the pedal force this valve releases air from one side to another.
Graduated Hand Control Valve:
This valve takes care of the parking brakes.
Brake Chamber:
The air from the reservoir flows through various valves and finally reaches the brake chamber which activates the S-cam in the brake shoe to apply the brakes in the front
Actuators:
The air from the reservoir flows through various valves and finally reaches the brake chamber, which activates the S-cam in the brake shoe to apply the brakes in the rear.
WORKING OF AN AIR BRAKING SYSTEM
Air brakes are used in commercial vehicles, which require a heavier braking effort than that can be applied by the driver’s foot. The following layout shows the arrangement of the air braking systems in heavy vehicles. Compressed air from compressor passes through the unloader valve and maintains its pressure. This air is stored in the reservoir. From the reservoir it goes to the Brake Chambers through many brake valves. In the brake chamber this pneumatic force is converted into the mechanical force and then it is converted into the rotational torque by the slack adjuster, which is connected to S-cam. This torque applies air brakes. Pipelines connect the brake system components.
IMPORTNACE AND DEFINITION OF RESPONSE TIME
There are different types of tests for measuring efficiency of air brake system. Two important tests are mentioned below.
Firstly,
 The efficiency specified for Brake devices shall be based on the stopping distance or the mean fully developed deceleration. The efficiency of a brake device shall be determined by measuring the stopping distance in relation to the initial speed of the vehicle or by measuring the mean fully developed deceleration during the test.
 The stopping distance shall be the distance covered by the vehicle from the moment when the driver begins to actuate the control of the braking system until the moment when the vehicle stops; The initial vehicle speed (V1) shall be the speed at the moment when the driver begins to actuate the control of the braking system; The initial speed shall not be less than the 98% of the prescribed speed for the test in question. The mean fully developed deceleration dm shall be calculated as the deceleration averaged with respect to distance over the interval Vb to Ve according to the following formula