When you test the tractor protection valve The Red air supply control knob should go into the?

The red knob is not the tractor protection valve. The tractor protection valve is at the rear of the tractor where the hoses connect to the tractor. The red knob is the trailer charge valve. It's also called a push/pull or PP valve. The yellow knob is tractor parking brake valve which is also called push/pull or PP valve. The red and yellow knobs share one valve that perform both functions.

The red PP valve being called the tractor protection valve is very outdated but was common at one time.

So I'm gonna be taking my pre-trip inspection test in a few hours, and I got to wondering. I know that the red trailer air supply valve is also called the tractor protection valve. Does that make the yellow tractor air supply valve the 'trailer protection valve', or is there no such thing?

no such thing

the red value is call the tractor protection valve because when pulled it protects the tractor air supply.. when pulled no air will leak out if the red/blue lines (bobtailing)

when pulled no air will leak out if the red/blue lines (bobtailing)

flood: --> so will it stay in the charged position if it is pushed into the charge position with the yellow tractor "parking brake" in "parking" position [extended] ?....

The red and yellow knobs share one valve that perform both functions.

bender: --> so where would we find mechanic level manuals for the valve and what is it called?.....the people who write the study materials we have to answer to insist on hiding that behind dash-board and getting a lap-monkey response for what it is called, most of them have never grabbed an air-line whipping at 60 psi and go blazitzo if you try to tell them the most air systems are not plastic knobs

Semi Crazy: Wait until they ask what the blue valve does!

Cyanotic Sunrise ...... from trying to read "study materials" written by Office Orifice

TP-3DC has to balance or not based on design parameters at the original concepting,....RED blocks at TP-3DC ... there is a complete "secondary" system with brake-chanbers showing on the .pdf so since we only see one brake chamber on most axles that I have seen a rupture of membrane in any place brings the whole system to "emergency" or "parking" as there cannot be a secondary & primary membrane in one air-chamber without overly complex force-moments further reading on MV-3 module may reveal industry standard and ASME information on what exactly the dual-knob dashboard control actually does

I have the .pdf saved to thumb-drive .... thx

flood: --> so will it stay in the charged position if it is pushed into the charge position with the yellow tractor "parking brake" in "parking" position [extended]

yes it will.... i do it all the time to check the trailer for air leakes when i hook to a trailer i pull the yellow hook up the air lines then push the red to check for air leaks when i pre trip the trailer pulling the red knob stops all air from going to the trailer (brakes and supply) pushing in the red supplies air to release the sping brakes, supply air to the air ride (red line) and to allow the brake pedal to send air to the trailer brakes (blue line) and yes if you have the red pushed and the yellow pulled the brake pedal will work the trailer brakes..

pulling the yellow cuts air to the tractor brakes only setting the tractor spring brakes (parking brakes) it also pops the red at the same time doing the same for the trailer, but you can push the yellow to move the tractor (bobtailing) and the red (still out) protects the tractor from losing air (red/blue trailer air lines)

i press the trailer air supply in when im parked bobtail sometimes. you would be surprised at the amount of water that will blow out of the lines. and yes, it can still blow water out of the lines even if you make it a habit of draining your tanks. not a bad thing to do now and then. just make sure you have the lines under control or they could fly around lol

TP-3DC has to balance or not based on design parameters at the original concepting,....RED blocks at TP-3DC ... there is a complete "secondary" system with brake-chanbers showing on the .pdf so since we only see one brake chamber on most axles that I have seen a rupture of membrane in any place brings the whole system to "emergency" or "parking" as there cannot be a secondary & primary membrane in one air-chamber without overly complex force-moments further reading on MV-3 module may reveal industry standard and ASME information on what exactly the dual-knob dashboard control actually does

I have the .pdf saved to thumb-drive .... thx

When they call the red (trailer) knob the tractor protection valve in testing etc you have no choice but to go with it and know what they are referring to (the red knob on the MV3 push/pull module valve) but the truth is that the tractor protection valve (marked TP on schematic) is an automatic shuttle valve that is designed to stop high volume air loss in the event of a severed or disconnected trailer air line or other trailer leak source. The red push/pull knob sends air to the tractor protection valve which in turn feeds the trailer.