What is the primary function of the supply line in an air brake system?

The primary function of the supply line in an air brake system is to deliver compressed air from the compressor to the brake chambers. This is crucial because the brake chambers are where the air pressure is applied to activate the brakes. When the driver applies the brake, it triggers the release of compressed air through the supply line, allowing it to enter the brake chambers. This pressurization causes the brake mechanisms to engage, effectively slowing down or stopping the vehicle.

The other options, while related to various functions of the air brake system, do not describe the principal role of the supply line. The brake pedal and other components interact with the air brake system, but they do not include the delivery function that the supply line provides. Knowing the correct function helps in understanding the overall operation and safety mechanisms of air brake systems in commercial vehicles.