The irrigation system that came with our house (looks like a DIY job) has a backflow protector on the main line and all the valves are anti-siphon. The valves are old and some of them leak so we're planning to replace them. I'm wondering if there's a reason why the valves are anti-siphon instead of inline. I've seen a few instances of this configuration on the Internet, but with no reasonable explanations.
As far as I know, our municipality doesn't have any rules requiring valves to be anti-siphon. In fact, we live in an area that can freeze overnight as late as June and as early as September, so moving to inline to get the valves underground would help make the system more resilient to freezing.