SpudFiles

pmalone wrote:thanks for all the help

how much of an advantage is there to using a piston valve over a sprinkler valve? and what is a good tutorial to follow to make one

Huge advantage. Once you get over 25mm in diameter(1") pistons start getting really effective and powerful.

For a 1.5" barrel i'd recommend a 2" piston valve. Though this is a tutorial I wrote and made, I still highly recommend you do a lot of research yourself so you know what you are doing, then you shouldn't have a problem follwing my tutorial as you'll understand most things,

If you don't understand it, you need to do more research.
Once you know enough, you should only really need to use my tutorial as a guide when you get stuck:

http://www.instructables.com/id/Golfbal ... That-Shoo/

just note that ball valves arn't always infeior, usually the projectile leaves the barrel before it's fully open, but on really larger systems it starts to take advantage of the high flow and the ball valve can be way better.
I know this guy personally who had a 12ft cannon made of DWV with a 2" ball valve, and it really annoyed me because his shot at near 800fps and my more professional cannons with modded sprinkler valves could hardly do half that