I've not decided on the flow meter yet.
Late to the conversation, but is there any reason any electric ball valve with manual override couldn't be used?
The manual override should just be a "Knob" on the top that rotates with actuation right?
Thinking something like this: http://www.oscsys.com/store/product/291
Then figure out a way to couple a rotary encoder to the manual knob to sense the real world position of the valve? http://www.oscsys.com/store/product/1001689
Parsing the output from the encoder should be a lot easier than all the crap you need to do to make a 0-10v transition with the controller.
But then again, I'm just guessing