that makes a lot more senses than the gauge just reads starting at 60 PSI (on my coach at least) thank you very much for taking the time to explain it. I've always wondered why the brake gauge will work fine but not the supply one, now I know 
not sure if everybody is like this with their coach but I love to know every little detail I can on why things work they way they do, it is fascinating to me.
It helps a lot to know this systems because before you get to know them they are like black voodoo magic stuff but after you tinker a little bit with it is not that difficult, at least on my coach, I've read than on newer coaches things are a "million times" more complicated (just teasing you Tom!)
not sure if everybody is like this with their coach but I love to know every little detail I can on why things work they way they do, it is fascinating to me.It helps a lot to know this systems because before you get to know them they are like black voodoo magic stuff but after you tinker a little bit with it is not that difficult, at least on my coach, I've read than on newer coaches things are a "million times" more complicated
(just teasing you Tom!)
1988 40ft Newell Classic
8V92 TA Mechanic
Allison 740 (4 speed)