Air Brake Components

While most cars use hydraulic breaks, which rely on compressing liquids, many larger, heavier vehicles, like buses and trucks, use air brakes, which rely on compressing gasses. According to the Iowa Department of Transportation, air brakes perform the work of three different braking systems: they are service brakes, for use during normal driving; parking brakes, for keeping the tires fixed while you are parked; and emergency brakes, for combining the above two braking systems during emergencies.

Compressor

The compressor of an air brake is responsible for pumping air into storage tanks, generating pressure. As the Government of New Brunswick notes, the vehicle's engine powers the compressor, which it is connected to via gears and shafts or pulleys and belts. While some compressors rely on the surrounding air for cooling, others use the cooling system of the engine. Similarly, while some compressors have independent oil reservoirs for lubrication, others use an engine's oil supply.

Storage Tanks

Air brakes typically use multiple storage tanks for holding compressed air, the precise number of which depends on the size and weight of the vehicle. According to the Government of New Brunswick, the primary tank that an air brake system uses is known as the wet tank, or wet reservoir, because it receives the majority of the condensation from the compressed air. The secondary tanks are known as dry reservoirs.

Tank Drain

At the bottom of storage tanks are tank drains, which allow water, oil and other fluids to drip out. Otherwise, these liquids could potentially freeze and cause air brakes to malfunction. While some tank drains are manual and require that you pull on a cable to open them and release fluids, others are automatic and open as fluids collect.

Governor

As the Iowa Department of Transportation mentions, the governor of an air brake is responsible for regulating when the compressor needs to pump air into the tanks. The governor will initiate the compressor when pressure in the storage tank drops down to the "cut-in" level, which is typically around 100 pounds-per-square-inch (psi). When pressure in the tank reaches the "cut-out" level, the governor will stop the compressor.

Pressure Gauge / Safety Valve

For drivers to see what pressure levels the storage tanks are at, all vehicles with air brakes use pressure gauges. These gauges display the psi levels of each tank. If the gauges reach dangerous levels (usually 150 psi or higher), safety valves in the tanks activate, releasing air and lowering the pressure.

Brake Chamber / Slack Adjuster

The brake chamber of an air braking system is responsible for capturing energy from the release of pressurized air and transferring it to the brake drums. When the tanks release air, the chamber moves away from the pressure, forcing itself against a push rod. This push rod, in turn, activates a slack adjuster, which converts the pushing motion of the rod into a twisting motion.