The PVB requires a minimum operating pressure to function properly, otherwise it will "gush". Find the leak. First try capping all your sprinklers on that zone and then run it. This will sometimes bring a hidden leak to the surface. If that doesn't work you will need to get into more involved leak detection.
I suggest/request the mods move this thread to the irrigation forum where this thread is more likely to be seen by people who deal with this kind of stuff on a daily basis, homeowner or not.