What type of valve should be closed when using double trailers?

When operating double trailers, it is crucial to focus on the correct management of the air brake system to ensure safety and proper operation. The shut-off valve plays a vital role in this context. This valve is designed to control the air supply between the two trailers in a combination vehicle.

By closing the shut-off valve, you can prevent air pressure from reaching the brakes of the second trailer during certain maneuvers or in case of a malfunction. This helps in maintaining better control over the combination vehicle, particularly during emergency situations or when the trailers are uncoupled.

Using the shut-off valve effectively can ultimately enhance the safety of driving double trailers, allowing the operator to manage the air supply to the brakes precisely. Other valve types, like a tongue valve or a blocked valve, do not serve the same purpose and may not provide the necessary control over the air brake system.