The 24 volt AC sprinkler valves that we used would not work on 12 VDC with pressure. They need about 18 volts to fire. You may have a similar issue.
You should connect them to the pneumatic breakout with that module being powered with 24 VDC as shown in the diagram Scott linked to in the thread above this.
We have done this for several years and it works fine.
Attached is an updated version of the same drawing. It shows how to get power for a 24 volt solenoid and this is even legal. Your circuit is fully protected.
I would suggest installing diodes across the coil to absorb the back EMF from the coil. Here is a link that explains. You can leave out the resistor.
http://en.wikipedia.org/wiki/Flyback_diode
You should see the green lights on the module change when you trigger the valve. Remember, you need a short pulse, about 0.5 second is good, so your code will need to make that pulse with a small state machine or you could just connect it to a button on the joystick and let the operator create the short pulse.
Have fun!
-Hugh