Tractor protection valve/air routing

Does it not say service (blue) and emergency (red) on the supply side?

 

Hope this helps

 

Something sounds janky. When you apply the trailer park brakes, you're exhausting the air from the trailer supply line. Nothing should be coming out. Did you mean when you step on the service brakes air comes out? That'd make more sense and I'd have to say you likely reversed the 2 lines from the truck that connect to that valve if that's the case.

The way the tractor protection valve works is that supply air is free to flow thru the valve whenever the red button on the dash is pushed in. There's a shuttle inside that valve that will move and allow service air to flow thru once the trailer service line is charged to a sufficient air pressure. If the 2 lines from the truck to the tractor protection valve are inadvertently connected backwards, service air will flow out any time the brake pedal or trailer spike is activated. However, you will never be able to charge the trailer air system as the shuttle in the tractor protection valve will be blocking the air flow.

 

Ok this is making more sense now. Where is the air actually blowing out at? The red gladhand? If so, that sounds like normal operation. You're not supposed to push the red knob in without a trailer attached. The tractor protection valve is only intended to protect service air from escaping. The valve with the red knob protects trailer supply air.

 

Just to be clear, pushing the red knob is not applying the trailer brakes. Its releasing them. It takes air to compress the big springs in the brake chambers. When you pull the knob, you exhaust air from the trailer supply line and that in turn exhausts air from the chambers, allowing those big springs to push the park brakes on.

 

Hi everyone, newbie here, can anyone give me some advice please. On my Freightliner Argosy the red knob on the dash doesn't pop out when the red trailer line is emptied. What part of the air system is likely to be faulty please.