Here's a cute little piece of work. There is someone out there who likes to build above-ground manifolds with standard zone valves, with poly pipe leading from valve outlet to under the ground. And of course, no backflow (maybe a swing check in the basement plumbing)
The addition of AVBs is my own, since I was tired of looking at them, and have little other use for them. It brought the system into genuine toxic-rated code compliance, for not too much money.