When checking the trailer's emergency brakes, where should the tractor protection control valve be positioned?

The correct positioning of the tractor protection control valve when checking the trailer's emergency brakes is in the "Emergency" position. This is crucial because when the valve is set to emergency, it allows the proper functioning of the emergency brakes on the trailer without any interference from the tractor's service brake system.

In the emergency position, the tractor protection control valve isolates the tractor's air system from the trailer’s air supply. This ensures that if there is a failure in the air supply to the trailer, the emergency brakes will engage, helping to prevent the trailer from rolling or causing additional hazards. It facilitates a proper system check, as it accurately simulates the conditions under which the trailer's emergency brakes would activate in case of air loss.

Setting the control valve to any other position, like normal or service, would not effectively engage the emergency brakes, potentially leading to safety risks since the emergency braking system would not be properly tested. Therefore, it is critical for drivers to understand that the "Emergency" setting is necessary to ensure that the trailer's emergency braking system is functioning correctly.