Have you ever wondered why we don't use hydraulic brakes in heavy trucks such as cars? The answer is very simple: air is available, useful and “safe”, while brake fluid leaks may cause catastrophic consequences when the system is stopped in heavy vehicles. Let us not forget that the air brake system is the heart of truck safety. Everything is based on a simple principle: use compressed air to stop thousands of kilograms of mass while moving.
In this article, we will learn about the parts of air brakes, their importance and why they are best for large vehicles. We will provide you with a set of tips to help you maintain and monitor this system as well.
The main components of an air brake system:
Now that we know that air brakes are the backbone of heavy truck safety systems, we should ask the following question: “What does this system consist of?”
Air brakes are not a single piece, but a complex network of parts that work together in harmony. Each part has a specific role in ensuring that you anticipate the truck when needed. If one part is missing or fails, the entire system may collapse. Therefore, understanding the basic components gives a clearer picture of the strength and reliability of this system.
- Air compressor and pressure governor:
The compressor system is located at the front of the vehicle. It is powered by the engine, and works to compress air and transfer it to the storage tanks. The governor's responsibility is to turn off the compressor when the pressure reaches a certain limit (usually between 120-135 psi), and also restart it if it drops to about 100 psi.
- Air dryer and air tanks:
After the compressor, air passes through the Air Dryer to get rid of water and oil. It is then stored in a tank known as the “Wet Tank” or the “Wet Tank” and then to the “Service Reservoir” for brake service.
- Security and discharge valves:
It includes safety valves that open when the pressure exceeds a certain limit (for example 150 psi) to prevent the explosion of the system. There are also water or oil drain valves that can be operated manually or automatically daily in cold conditions. An ethanol evaporator is used to avoid freezing the valves.
- Brake pedal and control valves:
Pressure is transmitted to the Foot Valve or Treadle Valve brake pedal, which controls the pressure sent to different brake circuits (front or rear), often with a “dual circuit” system for additional protection.
- Brake chambers and S-Cam:
When pressure is received on the brakes, the force is transmitted to the Brake Chamber, where the diaphragm pushes the (Pushrod) rod that actuates the “Slack Adjuster” lever and rotates what is known as the “S-Cam”, which in turn opens the brake shoe (shoe) towards the drum to create the friction needed to stop the wheel.
In some systems, disc brakes or wedge struts are used, but the control mechanism through air and pressure is similar.
- Relay valves and quick discharge:
In long trucks, air access to the rear axle may be delayed. Here, Relay Valves bring the response closer by sensing pressure at the brake pedal and then passing air directly to the rear brake chambers. To accelerate the application, Quick-Release valves are also used to quickly discharge air when the foot is removed from the brakes, and to reduce delay.
- Hand/emergency brakes (Spring Brakes):
The emergency system is very important as it has a powerful spring on which the cover is emptied when air is lost. It applies the brakes automatically and is controlled through an internal valve in the cabin or activated when the air is completely leaked.
- Warning tools (Wig-wag, Lights, Buzzer):
The system notifies the driver of low pressure by:
- A light or buzzer indicator when the pressure drops to 55—75 psi.
- Wig Wag: a mechanical arm that automatically enters the driver's field of vision to pull him into danger.
How does the system work step by step?
- Charging (Charging):
When the vehicle is running, the compressor starts working, and the pressure rises in the tanks. At sufficient pressure (which exceeds the minimum limit, such as 85-100 psi), then the system starts and the Release air brakes are removed.
- Applying the brakes (Applying):
When the driver presses the brake pedal, air is sent from the tanks to the brake chambers, pushing the S-Cam or the drum. It clings to the brake shoe and starts friction to stop the wheel.
- Release the brakes (Releasing):
When the feet are raised, air is emptied from the chambers, the brakes return to their original position with the springs, and the compressor automatically recharges the tanks.
- In case of loss of pressure:
If the system loses air pressure, the spring is discharged in the emergency room and the brakes are applied automatically. This mechanism is vital for Fail - Safe.
An air brake system is a system that uses air as a medium to transfer pressure or force from the driver control unit to the service brake, including the air—hydraulic brake subsystems.
Benefits and features of the system
- SUPERIOR FAILURE SAFETY:
If air is lost, the brakes are applied, not vice versa as in a hydraulic system.
- HUGE POWER:
A 16 in² chamber with a pressure of 100 psi generates 1600 lb power, and a 30 in² chamber produces 3000 lb force.
- Improved response speed relay & quick-release:
They reduce activation delay, preventing brake lag on long truck axles.
- Easy to maintain and diagnose:
Tools such as alarm and pressure luces, as well as easy-to-clean valves.
Maintenance, inspection and alert:
- Make sure the system pressure starts at around 100 psi, and disconnect the charge at 120-135 psi.
- Empty the air tanks daily, especially in cold weather, to ensure that the water inside the system does not freeze.
- Make sure the Wig-wag low pressure alarm or buzzer works. This system will help you if the system pressure drops suddenly.
- Check the relay and automatic adjustment valves (Slack Adjusters) regularly to ensure that the application or release of the brakes is not delayed.
- Check and replace the air dryer if necessary, especially in areas with high humidity.
To keep truck air brakes efficient, make sure to set the pressure between 100—135 psi, empty the tanks daily, test the low pressure alarm, and check the dryer and valves regularly.
Quick FAQ's:
- Will the driver feel the system working?
Yes, through the indicators, sudden air sounds psss and pressure when the brake pedal.
- What if the air is completely cut off?
The brakes are activated voluntarily by springs, which is their most important advantage.
- Does the system need air conditioning in the cold?
Of course, dehydrator and ethanol avoid blockage due to freezing.
epilogue
The air brake system in trucks is the driver's first safety shield and the best way to ensure an immediate stop even when the system fails.
Simply... Compressed air is what makes a truck stay safe on the road. Simple maintenance (such as emptying tanks and checking pressure) outperforms an emergency crisis, so keep your knowledge safe, and keep the truck always under control.
