Air brake is the most commonly used braking operation mechanism in heavy vehicles. The air brake has a similar function to the hydraulic braking system, but only that the air brake is powered by modified air instead of the hydraulic pressure used in hydraulic brakes.


 


 

Working
The operation of an air brake system is as follows:
The air compressor draws air through the filter and compresses it into the reservoir.
An unloader valve is provided between the reservoir and the compressor. The unloader valve protects the air pressure inside the reservoir beyond a certain limit.
The compressed air in the reservoir is conveyed through the pipeline to the brake valve as well as to other systems using compressed air.
The brake valve is operated by the brake pedal. When the brake valve is operated, the compressed air from the reservoir enters the brake chamber supplied to the axles, and the push rod provided by the brake chamber enables braking by activating the slack adjusters.

A pressure gauge is provided in front of the brake valve and a stop light switch on the front of the brake valve. (Pressure gauge helps to determine the amount of pressure in the reservoir, and the stop-lights behind the vehicle are operated by stop-light switches.)
A mechanical brake system provided in this connection acts as a parking brake.

Major Parts Of The Air Brake System
1. Air compressor.
2. Reservoir (or air tank)
3. Unloader valve.
4. Brake valve
5. Brake chamber (or actuator)
6. Slack adjuster.








Air Compressor

The air compressor is used to draw air, compress it and deliver it to the reservoir. The compressor operates by receiving a drive from the engine camshaft or crankshaft. Reciprocating type compressors are commonly used for this purpose.

Reservoir (or Air Tank) 

  The function of the reservoir is to store a large amount of compressed air required for brake operation. The reservoir helps to dissipate the heat generated by air compression into the atmosphere and to prevent the accumulation of oil and water vapor in the atmosphere.
A safety valve is provided at the top of the air tank, and if for any reason the unloader valves do not work, the safety valve can remove excess pressure from the tank and prevent the tank from exploding.
The joints in the tank, which are made of steel sheet, are welded with electric welding, and the drain plug, which is provided below the reservoir, helps to remove the accumulated waste and water.

Unloader Valve.

 

The unloader valve helps to prevent the pressure of the air filling the reservoir from rising above a certain level. It is also known as the Governor. When the pressure exceeds a certain level, the unloader valve operates and expels excess pressure air.
The unloader valve also blocks the flow of air (backflow) from the reservoir to the compressor when the air compressor is not running and the reservoir pressure is higher than the compressor's pressure.


Brake Valve

 

 The brake valve is the component that delivers the compressed air to the brake chamber and activates the brake. The brake valve also helps to control the intensity of the brakes according to the force exerted on the brake pedal.
The brake valve is operated by means of linkages from the pedal or by means of a slave cylinder.

Brake Chamber (or Actuator)

 

A diaphragm in the brake chamber divides the chamber into two parts. On one side of the diaphragm there is a hole for filling compressed air from the reservoir. The next part of the diaphragm is connected to the atmosphere by an air vent. Also the diaphragm with the spring is pushed to the part where the reservoir is connected. The brake is operated by a push rod connected to the diaphragm.

Working
When the brakes are not working, the diaphragm does not feel any air pressure, which is why the diaphragm is pushed back and the brakes are free.

 

Slack Adjuster.

 

A slack adjuster is provided with the wheels to adjust the brakes according to the wear of the brake linings. When the brakes are applied, the cam is rotated between the shoes via a slack adjuster.


To adjust the slack adjuster, loosen the nut (adjuster nut) attached to it, push the slack adjuster into the brake chamber, and continue until the shoes rest on the brake drum. Loosen the slack adjuster until the shoes are free from the brake drum and tighten the adjuster nut in this position.


When applying the brake, check the angle between the push rod and the slack adjuster so that the angle at which the brake is released (greater than 90∘) is equal to the angle at which the brake is applied.