What is the purpose of a relay valve in an air brake system?

Answer: B — To provide quicker application of the service brakes

The purpose of a relay valve in an air brake system is to provide quicker application of the service brakes. This component serves as an intermediary that enables the air pressure from the brake pedal to be transmitted more efficiently to the brake chambers on the drive axle. By doing so, it significantly reduces the reaction time when the brakes are applied, ensuring that the braking action is more responsive. This is particularly important in large vehicles, as it helps maintain control and stability during braking, enhancing overall safety. While other components of the air brake system contribute to the control and management of air pressure, the relay valve specifically focuses on improving the speed at which the brakes engage. Therefore, its primary function is to facilitate a more immediate response to braking commands, making it crucial for the effective operation of heavy vehicles equipped with air brakes.