That’s a good idea, thanks!
Yes, they have limit switches. There are a bunch of kinds…
-two wire reverse polarity to open or close
-three wire, common and + to one ot open, + to the other to close
-two wire spring return – + to open, 0 to close. (more expensive but failsafe)
24vac dpdt relay driven by open sprinkler output, with a dc supply to drive the valves could be wired to any of these types.
Also open sprinkler DC would run the spring return type directly, I believe… but i would have to replace my ac units.
we will probably make up a relay board.
We might also add a fifth relay to drive a clean water flush valve to clear the fertilizer water from the plumbing between runs. it gets complicated!