Sometimes I have to try and decipher what the post is really trying to say. I went with the conclusion that he was talking anti-syphon valves. I'm not sure why. Just a hunch. Also I've never seen a PVB gush water due to a broken lateral line. I've seen a lot but obviously nobody's ever seen everything. I hope he comes back with an answer.
Some PVBs will gush at low pressures - less than 20 psi, or thereabouts for a Wilkins 720, which will reseal itself when the pressure goes back up. But certainly, ASVs could also do the gushing thing.