What You Need to Know About Air Brakes

Air brakes are a braking system that uses compressed air to activate the brakes on a vehicle’s wheels or to supply energy to the braking system. This system can also include components that operate through hydraulic or other intermediate mechanisms.

What Is Compressed Air?

Compressed air is a gas (usually atmospheric air) that is pressurized to a level higher than atmospheric pressure using a compressor. This air is stored in reservoirs and serves as an energy source for various mechanisms, including braking systems.

Key Properties of Compressed Air:

1. Pressure Energy: When released, compressed air expands rapidly, creating a powerful flow that activates mechanisms.

2. Instant Action: Compressed air enables quick and efficient energy transfer.

3. Easy Storage: Compressed air can be stored in reservoirs until needed.

How Does an Air Brake System Work?

1. Pressure Creation:

• A compressor pulls in atmospheric air, compresses it, and directs it into reservoirs. The air is not merely transferred; its volume decreases, and its pressure increases. Compressed air remains pressurized in the reservoir due to its airtight construction. Even with some empty space, the air is confined, maintaining its high pressure.

• Pressure in the reservoirs is typically maintained at 8–10 atmospheres, which is sufficient for operating the braking system.

2. Pressure Transfer:

• When the driver presses the brake pedal, a valve opens, allowing compressed air to exit the reservoir..

• The air travels through pipes to the brake chambers near the wheels.

3. Brake Activation

• Compressed air pushes against a diaphragm or piston inside the brake chamber.

• This force is transferred to levers in the braking system, which press the brake pads against the drum or disc, slowing the wheel’s movement.

4. Brake Release:

• Releasing the brake pedal closes the valve, and the pressure in the brake chamber is released.

• Air is vented out through an exhaust valve, and springs return the brake mechanisms to their original position.

Why Don’t Air Reservoirs Burst?

Air reservoirs are made from strong materials like steel or aluminum alloys that can withstand high pressure.

If the pressure exceeds the safe limit, safety valves automatically release excess air to prevent damage.

How Does Air Enter the System?

The compressor pulls air from the outside through a filter, which removes dust and debris. The compressor works while the vehicle’s engine is running.

Compressor Modes:

• Active Mode: If the reservoir pressure drops, the compressor automatically starts to refill it.

• Standby Mode: Once the maximum pressure (8–10 atmospheres) is reached, the compressor shuts off until needed.

Why Is 8–10 Atmospheres of Pressure Important?

1 atmosphere equals normal atmospheric pressure (~101,325 pascals). A pressure of 8–10 atmospheres means that the air in the reservoir is compressed 8–10 times more than the surrounding air.

Benefits of High Pressure:

1. Efficient Energy Transfer: High pressure ensures powerful braking even with a small amount of air.

2. Compact System: Strongly compressed air requires less storage space.

3. Reliability: High pressure allows the system to remain functional even with minor air leaks.

What Is Hydraulics?

Hydraulics involves using liquids to transfer energy, based on Pascal's Law: pressure in a confined liquid is transmitted equally in all directions.

Hydraulic System Components:

1. Pump: Creates pressure by moving fluid (usually oil).

2. Cylinders: Convert fluid pressure into piston movement (Example: In a syringe, the piston moves when you press it, pushing out liquid. In a hydraulic cylinder, pressure moves the piston to perform work.).

3. Valves: Control the direction and volume of fluid flow.

4. Pipes: Carry the fluid to different parts of the system.

How Do Pneumatics and Hydraulics Work Together?

1. Pneumatic Component:

• Compressed air creates the initial pressure and serves as the main energy source.

2. Hydraulic Component:

• Air pressure can be used to activate a hydraulic system, where hydraulic fluid transfers force to the wheel braking mechanisms.

• This combination ensures smooth and precise braking, especially in heavy vehicles.

In some systems, compressed air drives hydraulic cylinders, which then use fluid to activate the brake pads.

Why Combine Pneumatics and Hydraulics?

1. Pneumatics provides power.

2. Hydraulics ensures precision and smooth operation.

3. The combination leverages the strengths of both technologies.

4. Redundancy in the system reduces the risk of brake failure.

Air brakes are a reliable and powerful system that ensures safe operation of large vehicles like trucks and buses. By using compressed air and, in some cases, hydraulics, these systems deliver effective braking tailored to heavy-duty conditions.