A tractor protection valve is:
A device that keeps air in the tractor or truck brake system, should the trailer break away or develop a bad leak.
A device that prevents theft.
A device that controls fuel levels.
A device that allows the battery to recharge efficiently.
On combination vehicles with air brakes, the tractor protection valve keeps air in the tractor or truck brake system, should the trailer develop a bad leak or break away from the tractor.