Valve Does Not Open

My neighbor has a six zone Hunter sprinkler system and the 1 inch valves on zones 1 & 2 do not open. The solenoids are getting power and I have disassembled the valves, cleaned them, and reassembled them, and still no luck. Even when I unscrew the solenoids, they still do not open.
I'm "dazed and confused"................
Eureka!!!! When cleaning the valve, I didn't notice another vent/orifice directly under the solenoid plunger. It didn't look like there was an opening because it had sand in it!!! I found a thin wire and shoved it through the opening, and the sand came out at the tip of the wire. I reassembled the valve and it works like a charm!!

If the solenoids don't actuate, they aren't getting enough current. Suspect poor wiring.

Look especially closely at the ground wire. The usual way to connect a series of valves to ground is to daisy chain them. There could be a loose connection in the links.