knightschade: Why not just use a sprinkler system valve? They sell them at Home Depot and Lowes and work off of dc voltage. They come in 3/4 and 1" outlets. Just use adapters to make it the size you need. I think the company is RainBird but I'm sure their are other companies as well. In the spring you can get them at the hardware stores for like $10.
Because he wants flow control and those pilot-operated valves only do on and off. They also need 24v to operate.