Which of the following represents a full service function on PA4 brake valves?

The full service function of PA4 brake valves is represented by providing full braking force. This function is crucial as it creates the necessary pressure in the braking system to stop a train or vehicle effectively. When the operator engages the brakes, the valve ensures that air is supplied to the brake cylinders sufficiently to achieve maximum stopping power, ensuring safety and control during operation.

In contrast, filling the pipe with air is part of the process leading to braking but does not represent the function of applying brakes. Reducing pressure is not appropriate in this context, as it relates to the action of releasing the brakes or modulating pressure rather than applying them fully. Activating emergency response refers to a specific action taken in urgent situations, but it does not encompass the general full-service function of the brake valve under normal operating conditions. Therefore, providing full braking force aligns directly with the primary purpose of the PA4 brake valves during standard braking operations.