Air Brake System: Components, Construction and Working

Heavy vehicles transport tons of goods and thousands of people from one place to another. Since these vehicles carry bulky goods that can compromise the balance of a vehicle while taking tricky turns, it demands a special type of braking system. This is where the importance of an air brake system kicks in. 

Air brakes help to adhere to safety guidelines. It uses compressed air pressure, unlike hydraulic braking systems that contain fluid that loses control when they leak. 

An air brake system or a compressed air brake mechanism is a friction brake mechanism for automobiles. In this system, compressed air that presses on a piston applies pressure to the brake pads to stop or slow down a vehicle. Here the foot pressure functions against a tensile diaphragm inside a brake chamber.

Large and heavy vehicles, especially multiple trailers, use this system. Besides, semi-trailers, trucks, buses and railroad trains also use this system.

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A dual air brake system consists of two different and separate air brake mechanisms. This system uses a single set of brake controls. Moreover, each system consists of hoses, lines, air tanks and other components. One system operates regular brakes on the rear axle.

Most automobiles with air brakes use a dual brake mechanism as a safe secondary action when the primary brake fails.

The components of the air brake system help in the proper functioning of this system. Below are its details:

Air Compressor

One of the significant parts of an air brake system is an air compressor. It functions with the help of an engine that uses a belt drive. An air compressor pumps atmospheric air using the required pressure and transfers it to its reservoir.

Storage Tank/Reservoir

The reservoir, or storage tank, stores compressed atmospheric air at high pressure. Since compressed air is responsible for the entire functioning of this system, the reservoir is a significant component. Storage tank reserves a sufficient air volume to help during brake application in case the engine halts or the compressor fails to function.

However, the size and number of reservoirs in an automobile depends on number of brake chambers and their size, along with the parking brake configuration.

Brake Pedal

A brake pedal in this system is an integral part of a brake mechanism. Drivers inside automobiles operate it. It is a form of a mechanical connection that helps to transfer input motion to the forward system initiating brake application and slowing or halting a vehicle.

Brake Actuator

This component is a type of piston-cylinder assembly that directly connects with the brake pedal. As a driver presses the brake pedal, it results in creating pressure throughout the arrangement.

Safety Valve

The safety valve in this system is a component that connects to an air storage reservoir. It prevents these reservoirs from bursting due to excessive pressure if the system malfunctions. It can happen as this air compressor operates continuously and supplies the compressed air inside the tank. 

The safety valve consists of a spring-loaded ball that allows air to push out from the tank into the air. Air releases when air pressure reaches a certain value. However, this valve's pressure setting is determined by the force of the spring.

Dirt Collector

This component is a small device that collects dirt and unwanted particles that the air filters separate. It is used before the triplet valve.

Foot Valve

Foot Valve draws compressed air from reservoirs when applying a brake. This valve, operated by foot, uses air to help the brakes to function. However, a driver determines the amount of air delivered to the brakes as per the distance of the brake pedal. This mechanism releases air in service brakes through its exhaust port.

Brake Drum

A brake drum is a significant component of this system that performs brake. It sits on the vehicle’s rear axle.

Braking Lines

Braking lines or supply lines are another significant component of this system. It shifts compressed air from the storage tank to a brake drum by simply breaking the lines.

Brake Chamber

A brake chamber is a circular container having a flexible diaphragm in the centre. It transfers the pressure of compressed air to mechanical connections. Service-brake chambers transmute compressed air pressure into mechanical movement, which applies to a vehicle’s brakes. This unit sits on an axle near the wheel.

Brake Assembly

A brake assembly consists of a brake chamber and a slack adjuster that sit on the backing plate due to steering action. Air pressure comes through an inlet port. The air pushes against the diaphragm and a pushrod which is connected by a pin and clevis to a lever or slack adjuster mechanism. 

This action changes the motion of a pushrod from a brake chamber to a twisting force of a brake camshaft. When air is exhausted, the return spring in the brake chamber shifts the diaphragm and pushrod to its released position.

Triple Valve

The triple valve is a crucial component of the air brake system as it helps in the entire operation of the system. Releasing and applying brakes needs a consistent application that this triple valve performs. As a driver presses the brake pedals, it forces pressure as it releases pressure immediately when the driver releases the pedals.

Air Filter and Dryer

Air dryers and filters are significant components of an air brake system. Manufacturers install air dryers between a compressor and a wet reservoir as it helps to remove moisture and humidity from the compressed air. On the other hand, air filters block dust particles from atmospheric air.

Only dry air must enter the air compressor as the moisture content might cause failure of the braking system. This happens as the water particles condense.

Air brake systems have a two-stage air compressor with gearbox shafts or a crankshaft. Here is what happens inside the unit:

• This system intakes air from the atmosphere, compresses it and delivers it to the storage tank through a valve. 

• When reservoir pressure attains maximum degree, the unloader valve opens.

• Then, the compressed air is directly released into the atmosphere.

• All four wheels with brake chambers have a diaphragm, which forces air pressure. This force operates the camshaft that runs the lever and applies brakes.

• Each brake chamber connects to a brake pedal, and an air filter fits between the brake valve and storage tank.

Below is a step-by-step procedure for the functioning of air brakes:

Step 1: When a driver starts a car's engine, the brake compressor activates as it functions by the engine. Then, the brake compressor starts compressing the atmospheric air. 

Step 2: Through the compressor the air that is compressed with maximum force flows to the compressed storage tank. It is the reservoir that contains some air reserved from its previous cycle.

Step 3: As the driver forces the brake pedals, the inlet valve opens and the outlet one closes. This gives the compressed air a chance to flow from the storage tank. It passes through the brake lines of the mechanism.

Step 4: Through the brake lines, the compressed air shifts to the brake cylinder. A brake cylinder consists of a piston inside its mechanism.

Step 5: As the compressed air flow forces pressure on the piston, it shifts away from its original place. It results in the conversion of pneumatic to mechanical energy.

Step 6: Brake drums sit on the wheel end of a brake cylinder. Moreover, there is a mechanical actuator which is like slack that consists of brake pads at its outer section. As this piston moves due to the force of the compressed airflow, there are expansions of the mechanical actuator inside brake drums. This function forces brake pads to move in an outward direction. It allows frictional contact with spinning drum lines.

Step 7: As there is frictional contact between moving drum lines and brake pads, its force on wheels causes your vehicle to halt or slow down.

If finding how do the air brakes work, it is explained in simple words below:

• Compressed air inside the air brakes activates the brake system. 

• This system consists of an air compressor, air filter, unloading valve, air reservoir, brake valve, and brake chamber.

• These compressors allow atmospheric air to flow through air filters and compress it. This airflow is reserved in storage tanks or reservoirs. 

• Air from this reservoir flows to several sections of the automobile that functions on compressed air.

• A section of compressed air flows into the brake valve, which a driver controls. A driver handles the braking intensities of a vehicle in emergencies.

Pedal Released: As a driver releases brake pedals, the master cylinder in this system shifts to its original position. It happens due to the piston spring, which results in the dropping of air pressure. This function allows releasing of brake shoes from a brake drum releasing brakes.

Pedal Depressed: As brake pedals are depressed from the storage tank, compressed air flows in all directions to brake chambers via brake valves and pipes in this system. This function allows the driver to apply brakes.

There are several advantages of an air braking system. Here they are as follows:

• The air brake system is an effective mechanism than the other braking mechanisms.

• It allows easy designing of chassis as the components of air brakes sit conveniently.

• It requires only air as a primary medium which is available in abundance.

• Air brake system ensures safety when applying brakes suitable for trucks and heavy vehicles.

• This system ensures better control and reduces stopping distance.

• The air brake system comes with a flexible hose connection and easily stores air at high pressures.

• This system is not prone to leakage as air is the major component. It is not the case with hydraulic brakes that use fluid to function.

• Air brake allows less wear and tear on components.

• Air fluid stores potential energy as it is compressed. So, it can control the force applied.

• Compressed air can be used for horns, tyre inflation wipers, and other accessories.

• Air line couplings connecting air tools to compressed air are simple to connect and disconnect, unlike hydraulic ones.

• The air brake mechanism consists of a fail-safe system that can stop a heavy vehicle even if it leaks.

So, now you have an idea about the air brake system and how it functions. It is the braking system that is preferred in heavy vehicles like trucks to minimise the risk of accidents due to sudden braking. 

Thus, it is also necessary to check whether it is working properly from time to time. For this purpose, you can consult a knowledgeable mechanic or send it to the workshops for regular service.