Pneumatic Toilet Paper/Spud Air Cannon-

This is a project I'm wiling on with my little brother. I'm building a cannon out of PVC. I want it to be able to shoot four times without adding air again. So my idea was to make four chambers to store the air. Each chamber would have an individual ball valve. Then another ball valve where the chambers stem into the main body and barrel of the cannon. From the three inch PVC Im going to drop back down to 2"-2.5" 
PVC for a more forced compression, then the barrel will be 4". I understand that PSI is a pressure measurement, however I'd assume that my PSI's wouldn't be able to exceed the lowest grade of PVC I build with? That would only make since. 

The problem I'm having is, I'm not sure if any stores such as home depot or lowes has couplets that could couple 4" and 3" as well as 3" to 2". I also need to know what kind of pressure would I need to get to launch toilet paper into about a 10-15 foot height? Or would this just be a trial and error experiment? 

Thanks for all help. It's much appreciated!

GASSYPOOTS5 years ago
my dad made a launcher for airsoft grenades almost like this i guess. for the valves he used sprinkler valves. for the trigger he used a press button switch and a 9V battery. it runs off of compressed air or compresed gases