What is the purpose of the tractor protection valve?

Answer: B — To prevent air loss during normal brake applications

The purpose of the tractor protection valve is to prevent air loss during normal brake applications. This valve is a critical safety component in a vehicle's air brake system, particularly when towing trailers. When a tractor is connected to a trailer, the tractor protection valve functions to maintain an air supply to the trailer’s braking system. If an air line were to break or become disconnected, this valve will automatically close, thus preventing a loss of air pressure that could compromise braking effectiveness. By ensuring a steady air supply under normal conditions while also providing protection against sudden losses in pressure, the tractor protection valve plays a vital role in ensuring safe vehicle operations and control.