The safety valve in an air brake system is designed to:

• A. Increase tank pressure
• B. Relieve excess pressure automatically to prevent over-pressurization
• C. Lock the brakes
• D. Power the parking brake

Answer: (B)

The safety valve is a pressure relief device that protects the air brake system from over-pressurizing. If the air pressure in the tanks or lines rises too high, this valve automatically opens and vents air to the atmosphere, preventing components from bursting or failing due to excessive pressure. It’s a safety backstop that ensures the system stays within its designed limits, rather than adding pressure or controlling brakes.

Relating to the other options: it does not increase tank pressure, so that function isn’t its purpose. It also doesn’t lock the brakes or power the parking brake; those functions are handled by separate brake controls and valves in the system.