What valve maintains the desired pressure in the brake pipe when the automatic brake handle is in the RELEASE position?

The correct answer is the regulating valve, which plays a crucial role in the operation of the brake system. When the automatic brake handle is in the RELEASE position, the regulating valve is responsible for maintaining the desired pressure in the brake pipe. This valve monitors and adjusts the pressure as needed to ensure that the braking system remains responsive and effective.

The regulating valve achieves this by maintaining a consistent pressure in the brake pipe, which is essential for the proper functioning of the entire braking system. It helps in creating the necessary conditions for smooth and controlled braking when the handle is engaged again.

In contrast, the other options serve different functions within the brake system and are not specifically responsible for maintaining pressure when the handle is in the RELEASE position. While the exhaust valve allows air to escape from the system, and the control valve manages the application of the brakes based on the pressure in the system, the pressure relief valve prevents excess pressure build-up but does not maintain the desired pressure in the brake pipe when the handle is released. Thus, the regulating valve's specific task is critical to the safe operation of the brake system during this phase.