Air Brake System - Parts, How It Works, Diagram, Principle, Benefits | learn mechanical engineering (2023)

table of contents

Introduction to airbrake:

An air brake, or more formally an air brake system, is a type of vehicle friction brake that uses compressed air pressing a piston to apply the brake pad pressure needed to stop the vehicle. Air brakes are used in large heavy vehicles, mainly those with multiple trailers that need to be connected to the braking system, such as trucks, buses, trailers and semi-trailers, in addition to their use in railway trains.

Air brake construction:

The air brake system consists of a two-stage air compressor driven by the crankshaft or driveshaft. It draws air from the atmosphere, compresses it and delivers it to the air tank through a relief valve. When the reservoir pressure reaches the maximum level, the relief valve opens to atmosphere. Compressed air is then released directly into the atmosphere.

Each of the four wheels, equipped with brake cylinders, consists of a membrane that is pressurized and pressed with compressed air. This force actuates the cam operating lever and applies the brake. Each of the brake chambers is connected to the brake pedal and the air filter is also mounted between the brake valve and reservoir.

Air brake components and their functions:

Following are the main parts of an air brake:

1. air compressor

  • It is used to increase and maintain air pressure.
  • The air compressor's job is to create and maintain the air pressure needed to operate air brakes and air-powered accessories.
  • A compressor is designed to pump air into a reservoir, resulting in compressed air.
  • The compressor is driven by the vehicle's engine, either by belts and pulleys or shafts and gears.
  • The compressor is constantly running with the engine. When the engine is running, the compressor is also running.

2) storage tank

  • The tank is used to store the compressed air. Reservoirs are pressure resistant vessels that maintain a supply of compressed air until it is necessary to brake or operate auxiliary air systems.
  • They must hold enough air to allow multiple braking if the engine or compressor fails.
  • The number and size of reservoirs on a vehicle depends on the number of brake chambers and their size, along with the parking brake setup.

3. Air dryer

  • An air dryer can be installed between the compressor and the wet tank to remove moisture from the compressed air.
  • It can be partially filled with a highly moisture-absorbent desiccant and an oil filter, or it can be hollow with baffles designed to separate moisture from the air.

4. Safety valve

(Video) Air Braking System (Parts & Working) (Hindi)

  • A safety valve protects the tanks from overpressurization and explosion if the regulator fails and does not place the compressor in the unload phase.
  • The valve consists of a spring-loaded ball that allows air to escape from the reservoir to atmosphere. Valve pressure setting is determined by spring force.

5. Foot valve.

  • The foot valve is used to extract compressed air from the reservoirs when needed for braking.
  • This pedal operated valve applies air to apply the brakes.
  • The driver regulates the amount of air supplied to the brakes depending on how much the foot or brake pedal is applied. When released, air from the service brakes is exhausted through the exhaust port.
  • The distance the rider depresses the foot valve pedal determines the air pressure applied, but the maximum application will not exceed the pressure in the reservoir. Releasing the foot valve pedal releases the brakes.
Air Brake System - Parts, How It Works, Diagram, Principle, Benefits | learn mechanical engineering (1)
  • When the rider applies the brakes by partially depressing the pedal, the foot valve automatically maintains the applied air pressure without the rider having to adjust foot pressure on the pedal.
  • When you release the pedal, application air is vented to atmosphere through the exhaust ports. Air pedals are spring loaded and have a different "feel" than hydraulic braking applications.

(v) brake chamber.

  • The brake cylinder is used to transfer the compressed air force to the mechanical connections.
  • Service brake chambers convert compressed air energy into mechanical energy and motion that apply the vehicle's brakes.
  • A brake chamber is a circular container divided in half by a flexible diaphragm.
  • The air pressure pushing on the diaphragm causes it to move away from the pressure, pushing the rod against the clearance adjuster.
Air Brake System - Parts, How It Works, Diagram, Principle, Benefits | learn mechanical engineering (2)
  • The force exerted by this movement depends on the air pressure and the size of the diaphragm. If the diaphragm leaks, air can escape, reducing the effectiveness of the brake actuator.
  • A brake cylinder is usually mounted on the axle next to the wheel to be braked.

(vi) Brake assembly

  • The brake assembly includes a brake chamber and a backplate mounted slack adjuster for steering action.
  • A brake cylinder is usually mounted on the axle next to the wheel to be braked.
  • Air pressure is supplied through an inlet port. Air presses against the diaphragm and pressure rod.
Air Brake System - Parts, How It Works, Diagram, Principle, Benefits | learn mechanical engineering (3)
  • The pushrod is connected via a shackle and pin to a crank-like lever called a "whip adjuster".
  • This converts the push from the brake chamber rod into a rotary movement of the brake camshaft and S-cams.
  • When the air is depleted, the return spring in the brake chamber returns the diaphragm and rod to the released position.

Air brake system function

When the brake pedal is pressed, the brake valve opens and compressed air flows into the brake chamber.

The brake valve consists of three stages.

1. Air intake

2. Escape

3. Brake chamber

When the brake pedal is pressed, the exhaust port closes and the air intake port opens, and compressed air flows back into the chamber. During the return stroke, the exhaust port opens while the inlet closes, expelling spent air to atmosphere. This system is equipped with a mechanical emergency brake that can be used if the air supply to the air brake system fails, called an air-assisted hydraulic brake system.

Air brake system diagram:

Air Brake System - Parts, How It Works, Diagram, Principle, Benefits | learn mechanical engineering (5)

Operating principle:

As shown in the figure, air brakes use compressed air (approx. 700 kPa) to operate the brake mechanism. The figure shows the complete structure of the air brake system. It consists of air filter, relief valve, air compressor, air tank, brake valve and 4 brake chambers. The compressor draws in atmospheric air through the air filter and compresses the air. This air is stored under pressure in the air receiver. From this reservoir, the air flows to various vehicle accessories, which are powered by compressed air. Part of the air goes to the brake valve. The brake valve is controlled by a driver who controls the braking intensity according to an emergency.

Pedal pressed: When the brake pedal is depressed, compressed air from the reservoir is evenly channeled in all directions through the brake valve into the brake chambers, further applying the brake.

Pedal released:When the driver releases the brake pedal, the master cylinder piston returns to its original position due to the return spring and the pressure is released. Disengages the brake shoes from the brake drum to their original position and the brakes are released

(Video) Brake System Components Categories

Difference between air brakes and hydraulic brakes:

Air brakehydraulic brakes
1. Compressed air is used as the working medium.1. Hydraulic oil is used as a working medium.
2. Air brake has more power than hydraulic brake.2. Hydraulic brake is less powerful than air brake.
3. Components: air compressor, relief valve, brake valve, brake chamber.3. Components: master cylinder, wheel cylinder, oil tank.
4. The air brake system is used in trucks, buses, trains, etc.4. Hydraulic oil brake system is used for light vehicles such as cars, light trucks, etc.
5. The air compressor consumes a certain amount of engine power.5. Engine power is not utilized.
6. It is not self-lubricating.6. Hydraulic brakes are self-lubricating.

Air brake system probable causes and solutions

No sir.Air brake system causes/problemsalternative solution
1.Too little air in the system.Identify the cause and eliminate it.
2.worn brake shoesrepair or replace
3.There is no air pressure in the brake systemIdentify the cause and eliminate it
4.Clogged or broken tube or hoseclean or replace
5.Leaks, faulty brake valveSubstitute
6.Brake shoe return spring, broken brake pedalsubstitute for cool
7.Leaking reservoir drain plugrepair or replace
8.faulty air compressorrepair or replace
9.compressor belt looseTighten correctly
10Leakage in pipes or fittingsrepair or replace
11stuck brake linkLubricate
12damaged air impellersSubstitute

Advantages of air brake system:

1. It is more effective compared to other brakes.
2. Air brake parts are easy to install where chassis construction is simple.
3. Compressed air can be used to inflate tires, horn and other accessories.
4. Uses only air as a readily available working medium.
5. It is easy to store high pressure air.
6. Provides strong braking effect, used in heavy vehicles and trucks.
7. Offers better control.
8. Shorten the braking distance.
9. Mainly allows less wear of parts.
10. It has flexible hose connector.

Disadvantage of air brake system.:

1. If there is a leak in the passage, the whole system will fail. Therefore, sealing the air is very difficult.

Air brake system applications:

(1) truck.
(2) bus.
(3) followers
(4) semi trailer
(5) Railway train.

More resources/articles

Automotive engineering parts and system notes, article
Automotive trends, news articles, notes
Basic concept notes of factual mechanics, article

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Sachin Thorat

Sachin is a B-TECH Graduate in Mechanical Engineering from a prestigious engineering school. He currently works in the sheet metal industry as a designer. He is also interested in product design, animation and project design. He also enjoys writing articles related to mechanical engineering and tries to motivate other mechanical engineering students through his innovative project ideas, designs, models and videos.

(Video) Working principle of train's air brake system | how train brake works | train braking system
  1. Hi,
    This is a very good post. This is a very informative and helpful blog. Thanks for sharing this article. Thank you for sharing the working details. I hope your next post will be published soon.


  2. Super


  3. The best explanation of the air brake system ever seen.


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