[jdkskyking]

The steering tag system is a closed loop system pressurized to 250 psi in conjunction with a pressure accumulator.  The accumulator has a ten year life span, the pressure should be checked annually. There is also a 230 psi pressure sensor mounted in a hydraulic block that turns on a light at the drivers warning panel.
The accumulator is mounted up high between the drive and tag axels. 
 
The system incorporates two actuators, the rear is the slave and can easily be seen by looking between the drive and tag tires. The forward actuator is a combination unit that also serves as the steering assist actuator but the two hydraulic systems are separate. The steering tag system is stand alone and does not use the engine driven hydraulic system. 

UPDATE NOTE:
3/2024 Time Frame.
I had my TAG hydraulic pressure set the the ZF recommended pressure of 15 bar/217 psi. 
The ZF RAS system is functioning as designed. No trouble at all when backing up. 
Reducing the pressure from 250 psi will improve the chances of steering the coach in the event of an engine driven hydraulic system malfunction (in my opinion) because the RAS closed loop hydraulic system acts on the forward “master” cylinder when steering straight ahead, which will impact the steering gearbox.