I've got a city park with 11 zones, all on municipal water supply. All of the sudden one zone only comes up to what I'm guessing is about half-pressure....only enough to raise the sprinkler heads up about a third-to-half way. Doesn't seem to matter too much if the valve is turned on manually, or by the clock, although the problem may happen slightly more often when turned on by the clock. It's a Hunter PGV valve, and isn't that old. I took the valve apart and inspected everything, which all appeared to be in good shape. There's no leaks anywhere to be found either. Anybody have any ideas or suggestions?