SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I have a similar situation, and so far, no answers. I followed the control wires from the controller in the garage, through the wall into a planting area where the tiny wires each entered a small cylinder about 1 inch diameter and 2 inches long. A much larger wire came out of this cylinder and the bundle (I think there are 4 control wires and a neutral) continued under a sidewalk. I found them on the other side of the sidewalk and followed them for about 2 ft. until they dove down at a 45 degree angle. I gave up when I was at about 18 inches deep because it was getting too close to a bush. I don't know what these cylinders are, but I put a box over them to make them accessible. Perhaps they are transformers to boost voltage?
Next, I tried following the outlet of the back flow preventer. I got about 16" deep to where it ran horizontal and perpendicular to the house and followed it for about 24 inches until it got to another sidewalk. I got tired of digging and backfilling (this is hard clay soil) and decided to try this forum to see if there is an easier way to locate the valves. BruceB

Professionals use locater equipment. Expensive, but worth it. Amateurs can try one on a rental basis. Your mileage can vary.