How Air Brake System Works in Automobile?

Air Braking System Diagram

Here you can get Air Brake System Working. Air Brake System are widely used in various vehicles but in heavy vehicles like trucks and buses due to the government vehicle regulations, air brake system is mandatory.

An air brake or, extra formally, a compressed air brake system, is a type of friction brake for automobiles in which compressed air pressing on a piston is used to use the pressure to the brake pad needed to stop the vehicle. Air brakes are utilized in massive heavy automobiles, mainly the ones having multiple trailers that need to be linked into the brake system, such as trucks, buses, trailers, and semi-trailers similarly to their use in railroad trains.

What is Air or Pneumatic Brake System

It is the types of braking system in which atmospheric air via compressors and valves is used to transmit brake pedal pressure from brake pedal to the very last drum or disc rotor.

  • Air brakes are specially utilized in heavy vehicles like busses and trucks because hydraulic brakes fails to transmit excessive brake pressure via more distance and also pneumatic brakes generates better brake pressure than hydraulic brake that is the want of the heavy vehicle.
  • The possibilities of brake failure is less in case of pneumatic brakes as they’re generally equipped with a reserve air tank which is available in motion whilst there may be a brake failure because of leakage in brake lines.
  • High cease vehicles nowadays are the use of air brakes system due to its effectiveness and fail evidence ability.

Working principle

As shown in the figure, in the air brakes the compressed air (around 700 kPa) is used to actuate the brake mechanism. The figure shows the complete format of the Air Brake System. It consists of Air filter, unloading valve, Air compressor, Air reservoir, Brake valve, and 4 numbers brake chamber. The compressor takes atmospheric air through the air filter and compresses the air.

This air is stored under pressure in the air reservoir. From this reservoir air goes to various accessories of the car which operates on compressed air. Part of the air is going to the brake valve. The control of the brake valve is done by a driver who controls the intensity of braking according to an emergency.

Pedal Depressed: When the brake pedal is depressed, compressed air from the reservoir is transmitted thru pipes similarly in all instructions to the brake chambers thru brake valve which similarly applies the brake.

Pedal Released: When the motive force releases the brake pedal, the master cylinder piston returns to its original role due to return spring, and the pressure is dropped. It releases brake shoes from brake drum to their: original position and brakes are released.

When the brake pedal is pushed the brake valve opens and compressed air is allowed into the brake chamber. 

The brake valve consists of three passages.

  • Air intake 
  • Exhaust 
  • Brake chamber

When the brake pedal is pressed the exhaust passage will be closed and Air intake passage open and compressed air goes back to the chamber. During return stroke the exhaust passage opens while intake closes and used air goes to the atmosphere. This system fitted with an emergency mechanical brake, which can be used when air supply fails the air brake system, which is called an air-assisted hydraulic braking system.

Main Components Of Air Brake System

1. Air compressor

  • It is used to build-up and maintain air pressure.
  • The function of the air compressor is to build up and maintain air pressure required to perform air brakes and air-powered accessories.
  • A compressor is designed to pump air into a reservoir which results in pressurized air.
  • The compressor is driven by the vehicle’s engine, both via way of means of belts and pulleys or shafts and gears.
  • The compressor is in regular power with the engine. Whenever the engine is running, so is the compressor.

2. Air compressor governor

It is the governing device used in air brake system that controls the compression pressure of the air that is pumped to the air storage tank via air compressor.

3. Air dryer

It is the device used to remove moisture content material from the air coming from the environment to prevent the lines and air storage from water condensation which could reason brake failure inclusive of at some point of winters because of the freezing of that condensed water.

4. Air storage (reservoir)

It is the tank this is used to store the compressed air sent by the compressor, this storage always has sufficient quantity of compressed air in order that the brakes may be applied numerous time and additionally prevents the brake failure whilst the air compressor shows malfunctioning.

5. Brake pedal

It is the mechanism this is operated through the motive force and is used to actuate the brakes on the way to prevent or decelerate the vehicle. Brakes, whilst pressed, driven the compressed air which in turn applies brakes to the shifting tire.

6. Dirt collector

It is the device this is placed inner a brake pipeline at place where a branch is separated and taken off to the triple valve which removes dirt from the air earlier than sending it to the triple valve

7. Brake cylinder or Brake chamber

It is the device that consists of a cylinder and piston over which the compressed air pressure is applied in order to push brake pads which in turn makes frictional contact with the disc or drum in order to stop or decelerate the vehicle.

8. Brake valve or Triple valve

The actuation and release of brake require continuous release and building of pressure inside the brake lines and brake cylinder according to the motion of the brake pedal this is done by the triple valve used in the air brake system.

9. Brake drums

The brake drum is the component through which the brake force due to frictional contact between brake pads and drum lining is transferred to the wheel in order to stop or decelerate the vehicle, Outer surface of the brake drum consisting of drum lining rotates with the wheel and the inner part consisting of brake shoes stays in its state of rest when the brake pedal is not pressed.

Note – Usually brake drums are used in air brake system but with suitable arrangement  disc brake can also be used in air brake system.

Why do We Need Air Brake System?

As we’ve already discussed brake system is the want of an vehicle automobile however as all of us realize while it involves the application every vehicle is not same as a few automobile are used for mild utility purposes like motors and motorcycles and a few are used for heavy purposes like buses and trucks, so there may be a want of exceptional braking systems because of the subsequent reasons-

  • As the load over mild vehicle and heavy automobile varies the brake force required to stop the heavy automobile is a ways extra than that of mild automobile, so the heavy vehicles have to be equipped with a braking system that can provide the enough brake force that can stop or slow down the automobile.
  • When we speak about  mild weight automobiles, hydraulic brakes provides more than sufficient brake force to stop or slow down the automobile because of its short size however on the subject of the heavy automobiles which might be huge in length the effectiveness of hydraulic brake machine is a high-quality problem.
  • As the fluid is used to press the piston in hydraulic braking machine the protection is the high-quality problem as though there’s any leak in the components of the hydraulic machine the performance of the braking is conveniently reduced or maybe misplaced completely, given that air is constantly to be had so the brake failure due to leakage is the less problem in the air braking system.

Difference between air brakes and hydraulic brakes

Air brakes

Compressed air is used as a working substance, it is more powerful than a hydraulic brake. Components: Air compressor, unloader valve, brake valve, brake chamber.The air brake system is used in trucks, buses, trains, etc.

Hydraulic brakes

Hydraulic oil is used as a working substance, they has less powerful than air brake. Components: Master cylinder, wheel cylinder, oil reservoir. Hydraulic oil brake system is used for light vehicles such as cars, light-duty trucks, etc.


  • Air Brake System more effective while compared to other brakes.
  • The air brake elements are easily located where the chassis design making is simple.
  • The compressed air can be used for tyre inflation wipers, horn, and other accessories.
  • It employs best air because the operating medium that’s effortlessly available.
  • Air Brake System easy to store air at excessive pressure.
  • It affords a heavy braking impact utilized in heavy motors and trucks.
  • It affords better control.
  • It reduces the stopping distance.
  • It mainly allows less wear and tear of parts.
  • It has a flexible hose connection.


  • If there is any leakage in the passage the entire system will fail.
  • Therefore sealing of air is very difficult. 


Due to its property of preventing brake failure air brake systems are widely used in various vehicles but in heavy vehicles like trucks and buses due to the government vehicle regulations, air brake system is mandatory.

  • It is used in railways
  • All the trucks and busses on the road today use air brake systems, few from them are.
  • Trailers
  • Semi Trailers
  • Railway Train.


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