Air brakes are used in many types of commercial vehicles, including trucks and buses. They use compressed air to operate the brakes at each wheel, and when the driver pushes down on the brake pedal (also known as a foot valve), it releases the air pressure, causing the brake shoes or drums to engage with the wheels. These systems are very important for safety on the road. However, like all systems on a truck or bus, they require regular maintenance and inspections to perform at their best.
Air Brake Safety Service
One of the most common reasons a truck or bus gets out-of-service is for air brake violations. If the air brakes aren’t working properly, a truck or bus can’t slow down or stop, which poses a danger to other drivers on the road. To keep your air brakes in top condition, follow these steps.
Unlike hydraulic fluid, which is typically black or green, air is a clear color, making it easy to see when there are leaks in the brake line. Also, the brake lines are less likely to get clogged with dirt than hydraulic lines because they don’t carry oil or other substances that could contaminate the brake system.
An air brake system consists of an air compressor that provides pressurized air to the system, and a series of reservoirs (also called tanks) that hold the compressed air until it’s needed. The system is controlled by an air compressor governor that activates the air compressor when the reservoirs are low (cut-in pressure) and turns off the compressor when the reservoirs are full (cut-out pressure).
When the brake pedal is pushed, the air from the supply reservoir is routed under pressure to the service brake chamber of each wheel. The air pressure overcomes a diaphragm and opens the s-cam, which applies the brake shoes or drum to the wheel. The brakes stay engaged until the driver releases the pedal, at which time the return spring closes the s-cam and the air is exhausted to the atmosphere.
The air from the supply reservoirs may contain moisture and oil traces that can damage the brakes, so each tank is equipped with a drain valve at the bottom to allow the crew to regularly clean out the tank. The tanks also have a fill valve at the top to allow crews to add more air pressure when necessary.
In addition to the air compressor and air tank, an air brake system also includes a control panel that displays a digital readout of the air pressure in each reservoir, along with other information, including an audible warning signal if the low air pressure alarm is activated. This control panel is used to monitor and record brake system performance during testing and retesting, as well as when the truck or bus is in operation. It’s important to keep the control panel in good condition, so it can provide accurate and reliable data. The air brake control panel is located in the cab, usually near the driver’s seat.