After sensing an increase in pressure, what does the control valve allow to exhaust through?

The control valve is designed to manage the air pressure in the brake system and respond to various changes in pressure. When there is an increase in pressure, the control valve specifically allows air to exhaust through the retainer. The retainer is a component that helps maintain pressure in certain brake applications. It holds the brake pressure steady during operations such as dynamic braking or when holding a train on a grade.

Understanding the function of the retainer is key in train handling as it helps in maintaining control over the braking system. This action of exhausting air helps to balance the system and ensures that the brake function is effectively managed, contributing to smoother train operations.

The other components mentioned, such as the brake cylinder, equalizing reservoir, and service line, have different roles in the braking system. The brake cylinder directly applies force to the brakes, the equalizing reservoir ensures there is sufficient air pressure in the system, and the service line is responsible for communication between the locomotive and the cars. However, when it comes to the specific action triggered by an increase in pressure, the retainer is the correct path for exhaust in this context.