What position (in/down or out/up) should the tractor protection valve be in when your bob-tailing?

It should be out or you will be outta air

The tractor protection valve keeps air in the tractor or truck if the trailer breaks away or develops a bad leak. The tractor protection valve is controlled by the trailer air supply control valve in the cab. The control valve allows you to open and shut the tractor protection valve. When the valve closes, it stops any air from escaping and lets the air out of the trailer emergency line which causes the trailer emergency brakes to come on. The trailer air supply control on newer vehicles is a red 8-sided knob which controls the tractor protection valve. Push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out and close the tractor protection valve when the air pressure drops into the range 20 to 45 p.s.i. Emergency valves on older vehicles may not operate automatically. There may be a lever rather than a knob. The normal position is used for pulling a trailer. The emergency position is used to shut the air off and put on the trailer emergency brakes.