Thanks, gentlemen. I got some pictures together that you can look at
here. Water comes in from the left, goes through the valve, and down to the mister at the bottom of the first picture. Close-ups of the valve follow.
Last night I cleaned out the valve and put new silicone on the connections. Tested it out this morning and the valve is shutting off correctly.
Thanks for pointing out the problem of mineralization; it is something I meant to address in the first post. Water here is very soft, so there should be little problem with mineral buildup. When it does become a problem, I will be able to get the scale off with a liberal application of a vinegar solution. If that doesn't work, then a stronger acid solution or coil cleaning spray should work. The whole house filter is a good idea--I'd like to get one when funds permit to take out chlorine.
We had a cold front come through earlier this week (unseasonably cool high in the low 90s) but the heat will be back in a week or two. That gives me time to get the kinks worked out.