When should red trailer valve pop out?

You got to have some ###### hands dude!

I've got some diagnostic skills, so my first thought would be hook it to a trailer instead of your hands.

 

The red valve should not be pressed in with no trailer attached. If you do, it’s normal for it to pop back out.

 

If it didn’t pop out, you’d lose all your air pretty quick out of your unattached glad hands. My guess is the dump truck must have a shut off valve at the trailer air connections for the red knob to stay in.

 

As far as I remember the brake check, the red knob needs to stay in even when the line is disconnected. It has to pop out at a certain pressure. I think it's 30 psi. Tractor protection valve.

 

Ok, I guess I’m not understanding why this is becoming a thing. It’s fairly simple and straightforward.

If you are not hooked to a trailer, the red knob stays pulled OUT. If you push it in like you would to release the trailer brakes, you will lose air pressure and the knob will pop back out. In other words…To drive a semi truck without a trailer, push the yellow knob in to release the tractor brakes. Leave the red knob alone. Pushing the red knob means you’re releasing the trailer brakes, but if you have no trailer why would you need to release trailer brakes? Just leave it alone and you’ll be all set. All the trucks I’ve driven for the last 21 years have operated this way…