[77newell]

There is a quick test to tell if it's a blown air bag or is something else. When starting the engine, immediately put the HWH leveling system in manual mode. This isolates all the air bags via the valves at the various 6 packs. If pressure builds normally with this setting of the HWH leveling system, but drops and stays down as you have described when you change the HWH to the travel mode, then you most likely have a leaky air bag. If the pressure continues to behave as you described, even in the manual level mode, then the problem is not an air bag (actually you could have a leaky bag but have a much larger leak elsewhere).

HPV is not a term I'm familiar with, but HCV (height control valve) is very familier. An HCV adds and subtracts air to the air bags while in the "travel" mode on the HWH panel to keep the height of the coach constant above the road surface as you move down the road. There are 1-2 of these valves on each axle, with the valve mounted to the chassis and a rod from the valve attached to the axle. Many 90's coaches had HCV's with plastic bodies that have been know to cracked and leak a lot of air which you can usually, but not always, hear by listening at the wheel wells.