When sliding tandems, why does air pressure have to be at 120+ before pulling red valve?

It looks to me like the answer is that when there is air in the red line, the air flow does not go to the tandem pins. And when there is no air in the red line, the air flow goes to the tandem pins. Is that correct?

 

No. It look at your diagram A. It does NOT show where the air is coming from.

You're making these assumptions that I know things that I don't definitely know.

 

Using the diagram you drew at the top of the page, it looks to me like the air flow in diagram A is from the tractor to the air tank.

 

In post #26, you say what you were ultimately shooting for when you took the time to draw the diagram. I made post #32 to ask you if I seem to have the gist of what you were shooting for. Could you respond to my post #32 please?

 

I just asked to confirm. I wanted to be 100% sure.

 

I'm not a construction worker or a builder.

Why won't you tell me if what I wrote in post #32 is correct? You took the trouble to make that diagram. You told me your purpose in making the diagram was to try to teach me why having air in my red line caused me difficulty in sliding the tandems. Well, you could make your drawing that diagram not be in vain if you would just address post 32

 

skallagrime does not seem to want to work with me any further on this. If anyone else who is reading this is knowledgeable about this stuff, I invite them to comment on what I wrote in post #32.