Air pressure Cannon

The launcher will shoot anything from a golf ball to a tennis ball at extremely high speed and extremely far. For wadding, a Pringles can or tennis ball can work best. For the valve, use a solenoid, modified sprinkler, or metal ball valve at least 1" in size, preferably at least 1 1/4". Valves with female threading allow the barrel and pc to be interchangable, so I would recommend them. Ranges vary by the pressure used and what you are firing.
Materials:
- [1] 1 1/4" metal ball valve or solenoid or sprinkler valve modified to open pneumatically
- [2] 3" to 1 1/4" reducers [or a combination that will get you from 3" to 1 1/4"]
- About 4-6 feet of 3" pressure rated PVC [most likely 260 PSI @ 73 degrees]
- [2] Male 1 1/4" couplers
- [1] 3" endcap
- Teflon sealant tape [thread seal tape]
- [1] schrader valve [3/8" and 1/4" are the most common sizes]]
- Saw
- Drill
- Drill bits
- PVC cement
- PVC primer

Note: 1 1/4" is just a suggestion. You can expect good performance with any size that is l" or larger.
Putting it together:
A fool could see where everything has to go without instructions, but here they are anyway. Remember to prime and glue each PVC to PVC connection and remember to use thread seal tape for all threaded parts. Don't trust "2 hour cement" - give your glue at least 12 hours [overnight works] before testing. Be sure to read the directions on the cans if this is your first DIY project.

The Barrel:
First, saw the 3" PVC into a ~3 foot piece and a ~2 foot piece. Take the 3 foot long PVC and attach one of the 3" to 1 1/4" reducers to one of the ends. Now take one of the 2 male couplers and fit it into the 1 1/4" part of the reducer. You may adjust these lengths to your own individual launcher and how long you want it to be. Generally, you want your barrel to be longer than your pressure chamber. 2:1 and 3:2 are commonly accepted ratios, though you don't need to follow them. However, making your barrel like 10 times as long as your pressure chamber is not wise.

The Pressure Chamber:
Take the 3" end cap and attach it on one of the ends of the 2 foot piece [or whatever length your pressure chamber is] of PVC. Now on the other end, push on the other 3" to 1 1/4" reducer. Then take the other coupler and place it into the 1 1/4" part of the reducer.

Putting Them Together:
Now you have the 2 ends of the couplers. Rap the thread seal tape around the area where the ridges are that make the connection between the 2 ends. You only have to put the tape on the PVC couplings and not the inside of the valve. Once the tape is there you can screw on whatever valve you bought.

Air Intake:
At the side of the end cap of the water balloon launcher's pressure chamber, take a drill bit [that is roughly the same diameter as your schrader valve] and drill a straight, clean hole. Now take your schrader valve and screw it in. This may take several attempts and you will need pliers for leverage. If you get the valve in straight, you won't need any glue! It will hold pressure perfectly when done correctly. We use a regular old bike pump for building up the air, although you could use an air compressor if you have one.

If you do use a compressor, you will want to buy an air coupler instead of a schrader valve. An air coupler is attached like a PVC fitting, so there is no need to drill a hole. Some people prefer this, though I have yet to actually find an air coupler, so I bid you good luck with that. With an air coupler, you also won't need an endcap. Instead, buy reducers and/or bushings to go from 3" [the size of the pressure chamber]to whatever size your coupler is.

You're Finished:
Congratulations you're done! When firing, remember that the ball valve needs to be fully closed. Make sure you never pump more PSI than the PVC is pressure rated for. The given ratings are often very conservative, but better safe than sorry. I wouldn't exceed 120 PSI, and you don't even really need more than 80 PSI. Cold air will weaken the PVC, so take that into account, such as while shooting snowballs.

NOTE: I find that unless something is a perfect fit (i.e slides to the bottom without being pushed but doesn't leave any gaps) you need a sabot. i find a small wooden wheel roughly the same width as the barrel works wonders on increasing the distance. Accuracy is a trial and error thing. Don't raise the pressure too much or the pressure chamer will blow up in your face. Not pleasant

Otherwise have fun.

DISCLAIMER: The original design can be found at http://soakermedia.net/water_balloon_launcher.php along with pictures of a completed cannon. I am not responsible for anyone's actions with this cannon. Nor am I responsible for someone who is injured through improper construction or not following the method correctly.