How to unclog a sprinkler system valve

I was able to get the sprinkler system line repaired and now I have a valve stuck open. I know I had to do this many years ago but I don't remember the details. I just tried unscrewing the cap for the valve in the valve box and much of it came apart, but I wasn't sure what to do with it at that point. So, I just put it back together and it seemed like it worked! For a few minutes anyway, then it clogged again. I guess I'll just go open it up again.
When I unscrew the assembly, the top of the valve come off and I see a black membrane with a tiny little metal tube in the center. Am I supposed to disassemble this further to get to what's underneath the membrane? I don't remember, and I don't want to damage the membrane by doing something it's not intended to do. Does it just pop off with a flat screwdriver? I'm tempted to try, but I won't use much force. I don't want to break the valve because then I absolutely would have to have someone come out to repair it.
Any thoughts?
Thanks! John
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wrote:

Crap. I just remembered that I forgot to put the spring back in. :-) I'd better go do that. heh heh....
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wrote:

Well, I went to put the spring back in and the membrane came out easily. That was when I found a freaking 1/4-inch screw stuck inside the valve! I took it out, replaced the spring and put it back together. It's still not working quite right, though. The valve doesn't completely shut off and I can't figure out why. I'm going to let it run for a little bit because my yard needs the water, but then I'll have to shut off the main supply valve to the system and then figure out what to do with that sticky valve.
Thanks, John
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Did the screw ding the valve seat?
Bob
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I don't know. It was just laying inside there when I removed the membrane. I didn't see anything else physically wrong, but I don't really know what to look for.
I have another problem. After running the water for a little while my valve box was filling with water. I've obviously got a leak but there was too much water in there for me to see where it was coming from. I may just have to bite the bullet and get someone out to fix it. I'll definitely be in over my head if any repairs have to be done in the valve box area.
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The only way to learn to swim is being willing to get in over your head. What can you lose?
Water leaks aren't rocket surgery.
Bob
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