I recommend these valves.
http://www.airbagit.com/Brass-Air-Va...irvalve-06.htm They are made of brass, rated for 300psi of
air pressure, open quickly and are easy to modulate. Plus they are designed to be able to replace the diaphragm.
http://www.airbagit.com/Air-Valve-Di...irvalve-16.htm
You can use a couple of them if you need more flow. We used them on my previous team when playing around with a t-shirt cannon and you could adjust the distance based on the length of the electrical pulse to the coil because they were so quick acting. In our case we used 4 which fed 4 ports on the back of the barrel. We did play around with only activating 2 solenoids at a time and the performance was adequate at that level in my opinion.