One way check valves for air tank

Typically you'll have a one way check valve for primary and secondary reservoirs. Primary and secondary tanks are fed by the wet tank. The check valves protect primary air from a loss in the secondary circuit and vice versa.



This schematic is typical of a pre-1997 truck without ABS.

 

some trucks got dual tanks with inner wall and valve inside tank.

 

shematic shown is too old, becouse now trucks have four separated air circuits

1- Rear brake
2 - front brake
3 Park brake release and trailer supply
4 accessory tank

but there are trucks of wierd design, like... Renault

They use two tanks and APM air processor.