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

One of my sprinkler lines only works when I manually open the valve. It's an irritrol valve, 205 I believe. A repair person told me the solenoid was bad, so I replaced it. The irrigation store also tested the old one and determined it was not working.
I installed the new one, but still the valve would not open when I turned the station 3 on at the controller. The valve would click and buzz, but no water would flow.
The solenoid definitely opens as it should. I switched the solenoid on line 4 to the non-functioning line 3, and still the valve on line 3 would not open. The new soleoid worked on line 4, which suggests that the soleoid is not the problem.
So, what should I do now? The valve has screws holding on the top, but I haven't opened it because I'm not sure what to look for. I'm definitely a novice at this stuff. I really don't want to replace the entire valve, so I'm hoping there is something else I can try.
To review--Line 3 works manually, but not with the soleoid. The solenoid works on another line, but not on line 3. There is a constant buzzing when the solenoid is on, but no water comes through the valve.
Help!

Thanks for the reply. As I said, I'm a novice when it comes to sprinkler repairs.
Are you referring to the plunger that's on the valve or or the solenoid? The plunger on the solenoid does retract as it should. Is there also a moving part, or plunger, on the valve below the solenoid, and is that what you're referring to? If so, does it come out using a small flat-bladed screwdriver, or what?
Thanks.

Okay, it finally works, although I now have a humming solenoid.
I dismantled the valve and reinstalled the diaphram assembly after taking apart the shaft, spring, gasket, and diaphram. A repair person had supposedly fixed a leak in this line, and I noticed he had stripped the screw heads and probably never checked to see if the line actually worked after the "repair." The fact that he was careless enough to strip most of the screw heads makes me wonder about the care he took with everything else.
Anyway, I can only assume that the assembly was stuck or that the gasket and cover assembly might have been installed incorrectly, or perhaps it was sticking.
I still don't know how the solenoid actually connects to the valve to open the diaphram--if someone can explain how the valve works, I'd love to know just to satisfy my curiosity--but for now everything appears to be working.
Thanks.