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

I have a LawnMate 7 controller with Wethermatic valves and Hunter sprinkler heads. This system was in place when I bought the house (70 year old house) so I have no idea how old the system is. Everything has worked well for last 2 seasons until now. This is a 3 zone system and the main zone for the front yard is not spraying.

I read up on the system (on this site) and did some work to try fix myself. I switched the solenoid from a working valve to the non-working, and the non-working valve still does not work, but the other valve still works, so it is not the solenoid. So the valve is stuck somehow. I openned up the valve and found a spring and diaphragm, which is intact. I can't figure out how to open the valve manually. I also did not see any debris.

Is anyone familiar with the Wethermatic valves and know how to open the valve manually or any other suggestions? I rather not replace the valve as the unit is old and I am not certain the newer Wethermatic valves will fit. The valve that I have looks like the Wethermatic 12000 series.

Please advice, thanks.