Adam, Orren is correct. However, just to satisfy my curiosity and perhaps lead to an additional problem, does the bus drop as air escapes?

With the bus running, the Norgren valves shift to run aux. air throught the ride height valve you have pictured into the air bags. When the correct height is reached, the arm moves to the center position and air flow, both in or out stops.

When you turn the key off, there is no air supply to the "air in" port on the ride height valve because the Norgren valve directing air flow has gone to the closed position.

That's why I ask the question to see if there is a secondary issue.