Which part of the air brake system is responsible for air storage?

The service tank, also known as the air storage tank, plays a crucial role in the air brake system by storing compressed air. This stored air is essential for powering the braking system when needed. During operation, the compressor generates compressed air, which then fills the service tank. The capacity of the service tank ensures that there is enough stored air available to apply the brakes effectively and efficiently, regardless of the load or operational demands.

In contrast, the other components have different functions. The compressor's primary role is to generate the air pressure needed for the system, while the relay valve is used to regulate the flow of air to the brakes, responding to the driver's commands. The brake pedal is simply the control input that the driver uses to initiate braking but does not directly store air. Thus, the service tank is the correct answer, as it is specifically designed for air storage within the air brake system.