How should the valves on the first trailer in a set of doubles be positioned?

The correct positioning of the valves on the first trailer in a set of doubles should be open. This is important because when the valves are open, the air pressure in the system can flow freely and maintain proper functioning of the trailer’s braking system. An open valve allows for effective communication between the trailers, ensuring that the brakes operate synchronously across both trailers during operation. This is crucial for safety, as the lack of proper air flow could result in braking issues, making the entire combination vehicle harder to control.

While closed or partially open valves may seem desirable for certain situations, they can inhibit the functioning of the air brake system, ultimately jeopardizing vehicle safety. The option mentioning that it depends on the load is not applicable in this context, as the standard procedure for set-ups involving multiple trailers mandates that the valves remain open to ensure reliable operation regardless of the load being transported.