How Does AirBrake System Work?

How Does the Air Brake System Function in Truck Air Brake System?
Compressed air is produced in the compressor which is joined to the engine and conveyed to the compressed air tanks. After passing by air tanks, the air arrives in the air dryer and the moisture is separated. The pressure is then adjusted in the pressure regulator.
The air (10 - 12 bar) leaving the pressure regulator comes to the multi-circuit safety valve, where it is divided into the vehicle's brake circuits (footbrake front-rear and parking brake), and the pressure is adjusted. The air leaving the multi-circuit protection valve comes to the brake pedal. The brake pedal is equipped with a foot brake valve (service brake valve).
Brake pedal valve (operating brake valve) is a valve which functions along with the brake pedal. Depending on the amount of brake pedal pressed, the compressed air is delivered to separate brake lines such as front wheels and rear wheels.
The air conveyed from the brake pedal (brake pedal valve) is delivered to the front axle relay valve. What is flowing here is not air, but air pressure. By the time the driver presses the brake pedal, the relay valve is controlled very quickly via a separate airline, upon the main valve is opened, pressure is applied to the wheel brake system. In other words, a small pressure is used to control a large pressure line. The relay valve minimizes the duration between the moment the brake is applied and the operation of the valve. Thanks to the relay valve, the brake pedal and the valve that controls the wheel brake operate synchronously, without delay. Compressed air conveyed from the relay valve is sent to the diaphragm brake cylinder - front axle brake cylinder that is located on the front wheels.
Diaphragm brake cylinder (brake bellows): the part where the braking force is generated. Both of them are located on the front two wheels. Compressed air is transformed into a mechanical energy in this part, by creating a pushing force, which enables the pads to be pressed against the drum. The front brake cylinder and the rear brake cylinder operate similarly, however differ in structure, the rear brake bellows also have a handbrake mechanism.

The diaphragm brake cylinder contains a steel spring, a diaphragm and a piston. The spring in a position as it is pushed back into the diaphragm. When the brake pedal is pressed, the compressed air coming from the brake pedal valve passes through the relay valve and the diaphragm brake cylinder in the wheel pushes the diaphragm and beats the thrust of the spring. By this way, the mechanism of brake is initiated. When the brake pedal is released, the compressed air in the diaphragm brake cylinder is released into the atmosphere.

Load Sensing Brake Valve (ALB Valve):
The braking force required on the rear wheels of heavy-duty vehicles depends on whether the vehicle is loaded or unloaded. For example, when a truck's body is empty, less braking force is needed to be applied to the rear wheels, whereas tons of loads require more braking force to safely decelerate and stop. ALB load sensing valve senses the load on the rear axles and increases the braking force in accordance with the amount of load. The ALB valve is mounted to the chassis at the rear of the truck, a rod along with the valve is connected to the rear axle (assembly on scissor-spring trucks). The load-induced collapse thus pushes the lever, allowing the valve to convey more compressed air to the brake bellows (air brake cylinders). Adjusts the brake according to the load amount. The ALB valve also has a relay valve, which also serves to shorten the duration between the brake pedal and the braking response. If the rod arm of the ALB valve is broken, the valve operates in accordance with a preset average braking load.

If the vehicle is equipped with an air (bellows) suspension system, the ALB valve functions sensitively to the pressure of the suspension bellows in this system.

Rear Brake Cylinder (Rear brake cylinder):
the thrust force required to push the shoe-pad to the drum is generated in the brake cylinder. In the air brake system, the brake bellows (rear brake cylinder with spring) are used in the braking mechanism of the rear wheels. There are a diaphragm, spring and piston inside the brake bellows and a spring and diaphragm for the operation of the parking brake system as well.
Air Brake System ABS Valves:
ABS valves are located separately for each wheel. The ABS valve is an electro valve, which opens and closes with an electrical signal. Normally the abs valves do not function, they are closed. The ABS control unit instantly reads the signals from the abs sensors (wheel speed sensor) on each wheel. When the brake is applied, if a slip-slide happens on the wheel (when it is about to slip), the abs system will activate and initiate the abs valves very quickly, send signals in order to open the closed abs valve. When the ABS valve is opened, the brake pressure sent to that wheel is released to the atmosphere and by this way, the braking force is reduced, thus preventing the wheel from slipping which occurs on the side that braking happens. Afterwards, the abs valve closes when the slipping stops and the braking force is increased.

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