I am still trying to get re-organized after the holidays but here is what our coach has.
First, we have only two air guages. One is for the front and the other is for the rear. As far as I know, each guage is for each portion of the entire air system (i.e. front or back) and includes both the bags and brakes. This is why you have three (3) air tanks. The first is a "wet" tank. The second half of this tank is the "Primary" tank whereas the second tank is considered the secondary tank...I think.
This was described this way to me by a Spartan tech. When in doubt, call Spartan and ask for a tecnician to help explain your chassis.
Remember that with air brakes, one of the tanks has to have enough air stored to release the emergency air brakes three (3) times at a minimum by law. This is a safety feature built in incase you cannot air up the system and need to move/tow the coach.
The air brakes have an emergency brake setup that uses a very large and powerfull spring (in each of the rear E-brake "cans") that engages the air brakes when the yellow knob is pulled. The "air" component is where air is used to compress the BIG springs via pressure on a thick rubber frisbee shaped diaphragm within the "cans".
Do NOT ever service these air brake cans yourself unless you know how to do it properly and have the proper tools as the springs are under such high tension that if they came loose, they would certainly seriously hurt you, someone nearby or worse.
Other than that, that is all I can suggest for now.
'98 Gulfstream Sun Voyager Bus - Platinum with 275HP/880Ft/# Cummins and Allison 3060