[77newell]

I believe it is possible if the key is on and there is no supply air being added and the diaphragm in the regulator is shot. In this case the the leak would drain the supply until the PPV at the service tank closes and then the air pressure will disappear quickly. If the HCVS are trying to raise the coach the air will flow backward through the HCVs and back through the 6 pack and ultimately out the leaky pressure regulator. Air is sneaky that way, it will go wherever it can.

If there is air supply, engine or other compressr, does the regulator continue to vent air.