Sounds like a defective or damaged part unless you have very large water pressure ??

Good Day ..

Should show signs of a defective casting. Heavy water hammer could do that kind of damage but I don;t think that part would be subject to water hammer.

It's hard to tell from the photo, but it looks like a Lawn Genie valve with built in vacuum breaker. The vacuum breaker is the part that broke, not the actual valve. Vacuum breakers just prevent dirty irrigation water from being drawn back into the pottable water supply line. Like Coho said, it should show some sign of manufacturing defect if that was the case. Water hammer or would more than likely be the culprit. That sudden impact over and over again can eventually weaken the plastic causing it to break over time.

There are two options, either replace this valve with another one of the same type, or install a normal irrigation valve and also install a Pressure Vacuum Breaker on the main line between the point of connection and the first valve on that line.

Curtis

Here is a link that might be useful: EvergreenSprinklers.com