I am trying to learn more about irrigation and decided to start by actually fixing one of the solenoids on mine. Anyways, the pipe that is shaped in an upsided down U above ground with a shut off valve, What is that used for? Does that help in some way with backflow prevention? Anyways, My sistem has five zones, 2 in front, 3 in back. I found the manifold box for the backyard no problem but cannot find the one in front. I thought I knew where it was and was digging there but couldn't find it. I don't want to dig all the way from the shut off valve until I find it so I was trying to find a short cut. The upside down U shaped thing is in the walk way from my front to back yard. I was thinking that that might, in some way, isolate the front and back yard. Could that be and if so wouldn't that mean that my manifold box for the front yard would be between that piping and the manual main shut off for the whole system? Thanks for any help. I appreciate it.