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

Recently I was in the yard and noticed the sound of running water coming from underneath one of one of the covers of my irrigation system. I lifted the cover and got a nasty surprise--water gushing out where it shouldn't. I've attached a notated photo to show where water was pouring out.

I assume this is some sort of pressure safety valve. There is construction in my area, so maybe the water pressure got too high momentarily and broke some sort of relief valve? I have no idea but I fear for my water bill, since I have no idea how long it was pouring out like that.

I've (of course) shut off the supply to the irrigation system. I've also opened the ball valves shown at the top of the photo, although I know that was pretty pointless.

I would greatly appreciate any advice on identifying the problem and how to fix it.

It seems to be a Febco 860U. I now have documentation and information on parts replacement. Thank you very much for the help.

Edit: I finally got around to messing with the 860U. My intention was to go through the troubleshooting steps outlined in the maintenance manual. (By the way, thank you for that, Febco.) But whatever debris had given the 860U problems must have worked itself out, because the relief valve was no longer open. Unfortunately, the debris seems to have lodged in one of my valves, because the sprinkler heads in one of my zones stay up and continually put out a small amount of water, even when the zone is shut off. If I had it to do over again, I would have closed the outlet shutoff valve on the 860U and opened just test cock #4 (as shown in the aforementioned manual) before restoring water pressure to the system. That way the debris might have exited to the atmosphere instead.