What does the trailer protection valve prevent?

The trailer protection valve serves a critical function in an air brake system, specifically designed to preserve air pressure within the trailer's braking system. When the driver disconnects the trailer from the tractor or if there is a significant loss of air pressure due to a leak, the trailer protection valve automatically closes. This closure prevents air from escaping the trailer's braking system, ensuring that the brakes can still engage and function properly even if there is a sudden loss of pressure.

By maintaining the air supply to the trailer brakes, the valve safeguards against situations where the trailer could become a hazard if it were to lose brake function while being transported. This feature is crucial for maintaining safety on the road by ensuring that the truck and trailer can stop effectively, especially in emergency situations. The design enhances overall vehicle safety by mitigating risks associated with air loss in the trailer system.