I recently renovated my backyard and made the mistake of lowering my existing anti-siphon valves below ground level into a valve box, not knowing that your not supposed to. The valves will still turn on manually, but not with the control panel. Now that I already did all of that work is there anything I can do to make it work, like adding a vacuum breaker or something like that? What exactly prevents the valves from operating when they are below the sprinklers?

If the anti-siphon valve is lower than sprinkler it will drain water from the sprinkler branch after sprinkler is deactivated. Small overflow will follow from the anti-siphon valve.

You could solve this problem by installing check valve on sprinkler branch that would hold water in disallowing it to push backwards towards the anti-siphon valve, for more info please open the link below, good luck.

John

http://www.irrigationtutorials.com/instal07.htm

Ok that makes sense. So I would need to install a check valve on the output side of each individual valve correct?