What does a dual parking control valve permit you to do with spring brakes?

• A. Release the spring brakes to move a short distance using pressure from a separate tank.
• B. Lock the spring brakes for parking.
• C. Override the service brakes during braking.
• D. Engage the emergency brake from the cab.

Answer: (A)

A dual parking control valve is designed to release the spring brakes so you can move the vehicle a short distance, using air pressure from a separate reservoir to overcome the spring force. In trucks with spring-applied parking brakes, the brakes are held on by strong springs for parking. To move the vehicle briefly, you deliberately apply air from the dedicated parking or secondary reservoir to the release chamber, letting the springs retract and the wheels turn. This lets you reposition the vehicle without using the service brakes.

The other possibilities don’t describe what this valve does: it doesn’t lock the springs for parking (that’s the role of keeping them engaged), it doesn’t override the service brakes during braking, and it doesn’t engage the emergency brake from the cab.