primary and secondary air gauge

Bad check valve on tank?

 

The check valve on your air tank is bad when the primary tank gets to a certain psi then the secondary tank opens and starts filling the secondary tanks the check valve only let's air in but not back out the same line check the valve at the main feed line to the tank air goes to the wet tank then to the primary tank and finally to the secondary tank

 

first of all identify air drier and tank filling valves

You may have valves on every tank ore four way valve like on european trucks.

As I remember valves are usually located in front bumper eream but if yoy got version with four way valve it is under driver's step

 

really there are two classical systems only. Generally there are four tanks.

1. Rear brakes
2. front brakes
3. park brake valve and trailer air supply + TCM
4. Auxially tank (cab suspention, tranny air servos (range, splitter ore auto), clutch servo (if used)

and some trucktors got additional air suspention tank.

Old system has valve for every tank, newer - four way valve

Ok some good handbooks
http://www.wsafc.org/WSFMA/Shared Documents1/Bendix Air Brake Handbook.pdf

http://www.meritorwabco.com/MeritorWABCO_document/tp20141.pdf

Really there are ultra new electronic air supply systems (Knorr Bendix EAPU, Wabco ECAM and other.....), they are smart, they save fuel (for example they use to apply compressor every time you slow down and use brakes), but classical systems are more popular now

In these handbooks typical systems are shown, but truck makers install additionak tanks, use dual tanks with wall inside and check valve (Freightliner), they use to combine Wabco, Knorr, Bendix and Haldex components.....