Your 9V valves are most likely based on latching solenoids, which means 1) they work only with DC power; 2) the circuit needs to be able to reverse the polarity of voltage applied to the valve in order to both open and close it. You can take a look at similar valves that I blogged about before:
OpenSprinkler Pi cannot be easily modified to control these valves. Instead, I have an upcoming product OpenSprinkler Bee that’s designed to work with these valves:
(scroll down to check the picture of OpenSprinkler Bee, and you can also sign up to receive notification when it’s available).