I have a Rainbird JTV/AS-100 anti-siphon valve. For some time now, when the valve is turned on (electrically, *or* manually with the bleed screw *or* manually with the solenoid) there's a satisfying "thump" and the sound of a healthy water flow. After 30 minutes-1 hour (sometimes less), the flow slows to a trickle, then stops. When I open the outgoing side, there's barely a trickle of water flow after an hour. There's an inline filter screen upstream that has been cleaned and water pressure at the filter's back end is *strong*. Thinking that this points to the diaphragm, I swapped it with an unused (but 3 year old) one. No change. [I have 4 other valves that work fine.] Is it possible that the solenoid is bad? I don't see how this can be since I can turn it on manually and there's no improvement. Also, the bleed screw should bypass the solenoid altogether. I also tried swapping the diaphragm housing. Again no change.

Suggestions?