What does a normally closed valve do in an air brake system?

Answer: B — Holds air in the brake chamber until brake pressure is applied

In an air brake system, a normally closed valve is designed to hold air in the brake chamber until brake pressure is applied. This functionality is crucial for the proper operation of air brakes, as it ensures that the brakes remain engaged until there is a deliberate action to release them, such as when the driver applies the brakes. When the air pressure reaches a certain level, the valve opens, allowing air to escape and engaging the brake mechanism. This design prevents accidental release of brakes during normal driving conditions, enhancing safety by ensuring that the vehicle remains under control. The valve’s normally closed position is an essential feature that preserves the pressure and stability needed for effective braking performance. Understanding the role of a normally closed valve helps in diagnosing issues in an air brake system and ensures that drivers and technicians can maintain the brakes effectively for safe vehicle operation.