Joe,

Water pressure may be too high. Check the pressure with a hose faucet gauge. Let us know what you are reading. Aloha

You may want to also call the manufacturer. Generally Orbit has a 6 or 7 year warranty on all products. They can help you troubleshoot or send you a new one. I know that's not something you want to do, but it may be the best thing to do.

Here is a link that might be useful: Orbit valves

Speaking from experience, I'd avoid Orbit whenever possible and stick with Toro or Rainbird. I installed some Orbit valves that gave me nothing but grief for several seasons. Oh what a hassle. I finally had them replaced with Toro valves and have had much better results.