We built one that runs off of just the kit compressor (fills tank in 10 seconds) and fires a shirt ludicrous distances, about 40 yards or so. Instead of a sprinkler valve, we used a pneumatically actuated gate valve (see it
here) that unleashes air stored in an abs reservoir into our pvc cannon. Overall it's a surprisingly simple and effective system, I'd suggest you look into it a little.
See the whole thread for our promobot
here. Maybe squirrel or GUI or MattH can give you a better description of how it works if you have questions...