I have recently redone a rising slope in my backyard with drought tolerant plants (I live in coastal S. Cal). However, I still need to water periodically during dry times. I also had my connection to the street modified, but now have 110 - 120 psi. I have old Champion 3/4" and 1" anti-siphon valves at the bottom of the hill, and the two 3/4" are now leaking heavily. I've replaced the gasket in the body, but that hasn't helped. I read that the anti-siphon feature is useless regardless because the valves are below the sprinklers. SO - do I need to reposition the valves at the top of the slope? Should I just replace the 3/4" valves with larger ones (assuming that water pressure is an issue)? And do I need to stay with Champion or can I go to different valves?
Anti siphon valve are required to be place 12" above the highest outlet.
Most Lilly the leaking you are seeing is due to back pressure due to the slope.
Personally I'm not a fan of anti siphon valves. I recommend using one standard double check valve or RPZ valve depending on the code for your area, then install standard valves- Hunter PGV. If you do this you will not have to move the valves all the way up hill. It looks a lot better and it's much more reliable.
I would also installing a pressure regulator before the Backflow device, this will prevent misting and premature wear and tear on the system.