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

Answer: B — To speed up the application and release of the brakes

The purpose of a relay valve in the air brake system is to speed up the application and release of the brakes. When the driver applies the brakes, the relay valve helps to quickly deliver air pressure to the brake chambers, ensuring a rapid response and thus improving braking efficiency. This mechanism is crucial, especially in larger vehicles where traditional brake systems may experience delay due to longer air lines and other factors. By immediately reacting to changes in the brake application signal, the relay valve minimizes the time it takes for the brakes to engage or disengage, which enhances overall safety and control while driving. This effectiveness is particularly important under demanding driving conditions, such as when descending steep grades or during emergency stops.