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

Some info on my system: New-to-me home, lived in 3yrs. Irrigation system is 20+ years old. Besides the replacement of a few sprinkler heads and a valve or two, have had no issues until recently. System has a Manual Anti-Siphon valve inline on pipe supplying water to a 3-valve sprinkler watering system for our grass.

My Anti-Siphon Valve:
https://www.orbitonline.com/products/sprinkler-systems/valves/plastic-valves/manual-anti-siphon/34-npt-341


Now my issue. One day after sprinklers ran, turned off automatically like always, water starting leaking from the ASV from the lid. I unscrewed it and noticed the spike/seal carrier was cracked. Due to the age of the ASV, I opted to replace the entire thing. Installed new one, turned water back on, no leaks. System cycled through later than day, ASV lid leaking again. Unscrewed, checked seal and spike/seal carrier, no issues, reassembled. Turned water back on, no leaks. System ran fine for 3-weeks. Came home yesterday, ASV lid leaking again after sprinkles cycle had run.

Why is it leaking? The ASV is new, internal parts ok. Does not seem to be any rhyme or reason. Its worked fine for 20+years so I know its not an design issue/flaw.

ANy thoughts?

FYI, Orbit said that its doing what its supposed to, preventing backflow. What they cannot answer is why its doing it when it hasn't ever done it for many years. Also, it does not stop, so in addition to flooding the yard, it won't seal up to give the sprinklers enough pressure to turn on when the sprinkler cycle kicks on again.