Air Brake System
What is Air Brake System?
Drivers greatly rely on their brakes when hauling thousands of pounds of weight in
trucks. The braking system on large trucks, buses, and tractor-trailers consists of air
brakes. Air-powered brakes are the safest choice in large vehicles since hydraulic fluids
can leak and cause accidents.
As a friction brake, an air brake utilizes compressed air exerting pressure on a piston to
apply the pressure to the brake pad or brake shoe required to stop the vehicle. Air
brakes are used in large, heavy vehicles, especially those with multiple trailers that
must be connected to the brake system.
In 1872, George Westinghouse first developed a safe air brake for use in railway service.
He made several changes to improve his invention of an air-pressure brake, which led
to various automatic brakes.
Since they are an important component of diesel vehicles, you need to know how air
brakes work and what are the parts and maintain an air brake system. So let's get
started.
Read Also: How An Anti-Lock Braking System Works? Advantages & Disadvantages
Parts of Air Brake System
The following are the important parts of air brake system:
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Air Brake System
#1 Air Compressor
The air compressor helps to suck atmospheric air into the storage tank or reservoir. It
compresses the air to the desired pressure and transfers it to the storage tank. An air
compressor is driven by the engine using a belt drive. A compressor may be air-cooled
or cooled by an engine cooling system.
#2 Storage Tank
A storage tank's purpose is to safely store compressed air sent through the compressor.
It is an essential part of the air brake system, as compressed air is responsible for proper
functioning.
It stores sufficient air and allows multiple brake applications if the engine stops or the
compressor dies. On a vehicle, reservoir size and number will depend on how many
brake chambers and their sizes are present, as well as how the parking brake is
configured.
#3 Brake Pedal
An air brake system is operated by driver input. The brake pedal is the primary part
that activates the brakes to stop or slow down the vehicle. It is a type of mechanical
linkage that transfers the input motion to the forward mechanism. As a result of
pressing the brakes, compressed air is forced into the tire, which in turn stops the
vehicle.
#4 Brake Drum
The brake drum is the sole part of the system that performs the braking process. During
vehicle stopping or deceleration, the brake force is transferred to the wheel by the brake
drum in the form of friction between the brake pads and drum lining.
The outer part of the brake drum has a drum lining that rotates with the wheel, and the
inner part containing the brake shoes remains at rest when the brake pedal is not
pressed. Generally, a brake drum is used in air brake systems but with proper
arrangement.
#5 Safety Valve
Near the compressor, a safety valve is usually installed in the storage tank. A safety
valve prevents the storage tank from over-pressurizing as the compressor continuously
works to supply the air.
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Air Brake System
It consists of a spring-loaded ball that allows air to escape from the reservoir to the
atmosphere. When the air pressure reaches certain values , the safety valves release air.
Read Also: Understand The Working Principle of Leaf Spring Suspension [PDF]
#6 Foot Valve
The function of the foot valve is to draw compressed air from the reservoir when the
brakes are applied. The amount of air supplied to the brakes is controlled by the driver
according to the distance of the treadle or brake pedal.
By moving the foot valve treadle, the driver controls the amount of air pressure applied,
but the maximum pressure shall not exceed that in the reservoir. Releasing the foot
valve treadle disengages the brakes.
#7 Brake Lining
These are known as supply lines. Transfers of compressed air from the reservoir to the
brake drum are made by simply breaking the brake lines that connect the reservoir to
the brake drum.
#8 Dirt Collector
A dirt collector is usually placed inside the brake line and branch pipe. It collects the
dirt particles separated by the air filter. This helps separate the dust from the
compressed air coming through the brake pipe so that only clean air enters the valve
and reservoir.
#9 Brake Actuator
A brake actuator is a device consisting of a piston-cylinder arrangement that is directly
connected to the brake pedal. As the driver depresses the pedal, it builds up pressure
throughout the assembly.
#10 Triple Valve
A triple valve is also an important part of the air brake system. It is used to apply and
release the brakes, requiring a continuous applying and releasing mechanism. It applies
pressure as soon as the pedal is pressed, while it immediately releases pressure when
the pedal is released.
Read Also: Drum Brake vs. Disc Brake: Which Brake is Best?
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Air Brake System
#11 Air Filter and Dryer
As the name suggests, air filters remove dust particles from the atmospheric air, while a
dryer inlet removes moisture and humidity.
If the air brake system lacks a dryer, it causes water condensation in the lines and air
storage, resulting in brake failure during winter due to freezing that condensed water.
Construction of Air Brake System
An air brake system comprises a two-stage air compressor driven by the crankshaft or
gearbox shaft. In this braking system, the air is taken from the atmosphere, compressed,
and then delivered to the reservoir through an un-loader valve.
When the pressure of the reservoir reaches the maximum degree, the unloader valve
opens to the atmosphere. The compressed air is then vented directly into the
atmosphere.
Each vehicle wheel fitted with brake chambers has a diaphragm to which air pressure
applies and pushes.
This action produces a force that operates the cam actuating lever and applies the brake.
There is an air filter between the brake valve and the reservoir of each brake chamber,
and the chambers are connected to the brake pedal.
Read Also: How An Electronic Ignition System Works?
Working of Air Brake System
The above figure illustrates the layout diagram of the air brake system. These brakes
generally consist of an air filter, unloading valve, air compressor, air reservoir, brake
valve, and brake chamber.
Initially, the compressor carries air from the atmosphere through an air filter. The air
filter filters the air and transmits it to the compressor, where it gets compressed. This
compressed air is then sent to the reservoir through an unloader valve, which opens at a
predetermined reservoir pressure and is connected to a brake valve.
From the brake valve, tubing extends to the front and rear brake chambers. Air is
supplied to the brake chambers on each wheel through brake valves. It is controlled by
the driver, who can determine how intense the braking should be.
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Air Brake System
Brake Applied
In the diagram above, air at full system pressure is directed by the dark shading (red) in
the brake line connecting the supply reservoir to the foot valve. The driver does the
work of braking. This can be seen by light shading (pink) in the lines connecting the
foot valves to the air chambers.
As the pedal is depressed, the air is compressed from the reservoir and sent evenly in
all directions through the brake valves to further apply the brakes.
Brake Released
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Air Brake System
In the above diagram, the driver's foot is off the brake pedal, releasing the brake. As a
result, the exhaust port at the bottom of the foot valve has opened, allowing air to
escape from the brake chambers.
As soon as the brake pedal is released, the return spring causes the master cylinder
piston to return to its original position, reducing the pressure. Now, the brake shoe
return spring has forced the brake lining away from the brake drum.
Read Also: 10 Common Brake Problems That Every Driver Should Know
Advantages of Air Brake System
1. These brakes include an air tank that stores sufficient energy to stop the vehicle if
the compressor dies.
2. Air brakes are more effective than other brakes.
3. These are effective even with leakage, so an air-brake system can be designed
with sufficient capacity to stop the vehicle safely even if there is a leak.
4. To operate the brake, only air is required, which is easily available.
5. Compressed air can be used for auxiliary applications that are unsuitable for
hydraulics, such as air horns and seat adjusters.
6. Air line couplings are more accessible to connect and disconnect than hydraulic
lines.
7. It provides a higher braking effect as well as better control over the system.
8. In this system, the wear and tear of its parts are less.
Disadvantages of Air Brake System
1. Air brakes are generally more expensive than hydraulic brakes.
2. This compresses the air, resulting in moisture that requires an air dryer to
remove, which makes the system expensive and can lead to high maintenance
and repair costs.
3. A faulty dryer causes ice to build up in the air-brake system in winter.
4. Air brakes produce noise in the range of 95–115 dB (decibels), with levels close to
115–120 dB for a typical noise level range capable of causing immediate hearing
damage.
5. If a leak is found along the way, the entire system will fail, so air is very difficult
to seal.
6. Air brakes do not work underwater and in extreme temperatures.
Read Also: 6 Most Common Problems of Cooling System [How
to Detect Them]
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Air Brake System
Application of Air Brake System
1. The use of air brakes becomes necessary in the case of many trailers, high-speed
long-haul buses, military utility vehicles, and trucks with semi-trailers.
2. George Westinghouse invented air brakes used for trains.
3. After proving their efficiency in trains, air brakes were later adapted to heavy
vehicles.
4. They are also used in small vehicles, but there is less space for applying air
brakes.
5. There are also air brakes that are used in buses to provide braking.
Wrapping It Up
I hope I have covered everything about the “Air Braking System.” If I missed
something, or if you have any doubts, let me know in the comments. If you liked this
article, please share it with your friends.
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