I recently purchased an acre home with 11 irrigation zones and am concerned with two zones where emitters are higher in elevation than their zone valves. My water service splits after the meter into two separate valved atmospheric vacuum breakers. One is for house service, the other for landscape irrigation. On the irrigation side there is a bibb line and supply line leading out to other areas, then a 5-valve manifold (each valve is a 1" brass anti-siphon valve). Two of those zones have emitters 3 feet higher in elevation than the ASV and the AVB. The emitters are all drip manifolds connected to 3/4" PVC laterals.

One of the two valves needs to be replaced, which led me to researching valve types, which taught me that the valve needs to be 18" above the highest emitter downstream, which led me here.

It would be incredibly difficult to run a new supply to the elevated area (many large boulders). So I'm wondering whether drip heads at higher elevation than the valve is an issue (I would imagine this occurs when folks drip their hanging plants and the like). If so, would a check valve just before the heads running above level suffice? I don't want to discharge back flow into the water supply.