Sprinkler System Backflow From Elevation Change

[Nessism1]

I just finished installing a two-zone sprinkler system in my backyard. One zone has a small section that's at a higher elevation than the control valves. I did a brief test before filling the trenches to check for leaks, and when I shut off the valve, water flowed from the anti-siphon/backflow prevention portion of the control valve.

I'm thinking about installing a secondary Pressure Vacuum Breaker valve in the system to further protect the potable water supply, but that won't stop the water from backflowing out of the valve every time the system is used. Replumbing the system, elevating the valves, is an option, but an unsightly one, since the valves are on my patio. I built a box to protect the valves, and that work looks for naught at this point.

Open to suggestions.

 

[Lawnman23]

I am not a plumber, just looking at the setup but why not just install a one-way check valve between the control valves and the supply side? It would require redoing some of your nice work but would still fit under the box when done.

Something like this for instance.

 

[alarmguy]

Have you ever lost water service at your house?
If not, I wouldn’t be concerned, however @lawnmans suggestion should put you at ease