Instructables
While not particularly new or creative, here are my plans for a simple pneumatic (compressed-air powered) potato cannon. It can also be used for other projectiles, as long as they fit down one of the interchangeable barrels. It uses an electrically operated valve, originally made for in-ground irrigation systems.

This project is also documented on my website at: http://www.mbeckler.org/pneumatic_cannon/
 
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Step 1: Safety Warning!

Safety Warning: Please be careful with this project. From what I've heard, PVC is not meant for holding compressed gasses. Gasses compress much easier than liquids, so be careful. The sprinkler valve used is designed for cold water, so be careful. The pressure gauge is designed for cold water applications, so be careful. Almost nothing in this project is used in its intended purpose, so please be extra careful. If you explode one of your PVC pipes, you will have essentially detonated a pipe bomb, and you are going to be in a world of hurt. You might want to take an old pair of jeans, cut off one leg, and wrap it around your pressure chamber. You can also use an old towel, or some metal screening. It probably wont help in the event of a pipe rupture, as one user has suggested. He also reminds us that some PVC is not actual PVC through the entire wall of the pipe. He says that 'cellular core' pipe, which is not rated for pressure, has a lightweight foam core, surrounded by thin layers of actual PVC. Please double check your pipe before purchasing, to ensure that you are not purchasing cellular foam core pipe. Another user has written that fiberglass mesh tape, used in construction for drywall joining, might be a stronger pressure chamber coating. Another user suggested taking coupling, sanding off the inner stops, and gluing them to the outside of your pressure chamber.

If you only remember one thing from all my safety warnings, remember this: PVC shrapnel will not show up on an X-Ray. The doctors will have an extremely hard time picking all the plastic shards out of your body if something goes wrong. You have been warned.

organicengines adds a helpful reminder to keep your PVC out of direct sunlight, because the light will degrade the plastic and make it brittle. Be careful!

Yes, this could be a dangerous project. I'm not a lawyer, but I'd like to say that I'm absolving myself of all responsibility for your actions. If you decided to build one of these cannons, by all means have fun, but please be safe. I'm not responsible for anything except for fun. If any of the Instructables administrators or moderators feel this project is too dangerous for this website, I will gladly remove it as soon as possible.

Another safety point: This is a cannon, which is a type of gun. Guns are meant to be dangerous, they would be pointless if they weren't. If you have no experience handling guns, please be very careful with this project, and do yourself a favor and take a firearms safety course. It will be a good experience even if you never shoot a gun again. If you have experience with guns, please be careful regardless. When I went through hunter's safety, they taught us three important rules of firearms safety:
1. Treat every gun as if it is loaded, so always point it in a safe direction. This means not at you, your dog, or anybody standing around. Point it up in the air, or down at the ground.
2. Always keep your finger off the trigger (valve switch) until ready to fire. Enough said.
3. Know your target and what's beyond. Plywood, fences, and garage walls are not strong enough to stop some of the things you can shoot with this cannon. I've put clean holes through both walls of an empty 55 gallon steel drum, so know what's behind your target. Try to not shoot this cannon in residential areas, or use really low pressures and soft projectiles. Soft projectiles include rolled-up, wet socks (more on this later), water, and loose snow.

That being said, this cannon can provide hours of entertainment, as well as a bit of education, in projectile physics and the ideal gas law.
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Masher0074 months ago

This is not spam, but a warning. PVC will fail suddenly after a while. This was band member that hurt badly by a T-Shirt launcher explosion.

https://fundrazr.com/campaigns/1Zs3c
..

DanTDM7 months ago

They do not have compatible threads. Buy a pressure gauge with a 1/4 inch thread and use a bushing reducer. It will also be easier to read. Yours is for garden hoses, not pipes.

I do find the pneumatic vale
http://www.air-matics.com/Pneumatic_valve/
akossoy1 year ago
Very similar to my ible but mine is a sniper instead of a cannon. It looks great and well attached.

Well done! :D
I would love to see an ible of yours.
TurboFusion2 years ago
What would happen if instead of a PVC pipe for a air tank, you used a copper pipe? I suppose the increased strength of the tank would lower the risk of rupturing and allow you to put more pressure into it.
matthewbeckler (author)  TurboFusion2 years ago
I suppose you could use higher pressure and have less chance of a rupture. Also pieces of copper embedded in your body will show up on the x-ray so the doctors can pull out all the pieces, if the worst comes to worst. Honestly I think the pressure limitation comes from the valve primarily, so if you switched to a ball valve or other value instead of the electric diaphragm value, you could use higher pressures with the same PVC. Perhaps the best option would be an all-metal design with a piston valve (info here http://www.spudfiles.com/spud_wiki/index.php?title=Piston_valve) ?
url for your website doesn't work
Thanks for the heads-up, I just fixed it!
epierce2 years ago
Have you ever considered building a "P" trap tipe loop to contain the water before it is fired?
matthewbeckler (author)  epierce2 years ago
Huh, that's a good idea, I might have to try that sometime. Sort of like a mini reservoir for the water. I wonder if you could use something larger too...good idea!
de05092 years ago
hello bro. This is one idea i did for kinda safe projectiles, didnt document it anywhere but the idea is simple. I mashed newspaper and inserted into PVC pipes, then compress to squeeze the water out. make them real dry and then remove from mould and dry under the sun or other means for drying. Its ready now but i prefer to coat them with a clear cellophane tape for more durability. Can be substituted with foam things, but the density of paper makes the hardness and inertia feel just right. i dont know why, but it feels just right. And its cheap
kayu2 years ago
how can i make littel one of it anyone no ?
knuckel4 years ago
mine is like yours but HUGE
SANY1154.JPG
kayu knuckel2 years ago
mine has an oxigen tank lol :)
urtlesquirt2 years ago
never knew guns can kurt you.
Dashadower2 years ago
Is the ideal gas law Pv=nRt?
matthewbeckler (author)  Dashadower2 years ago
You are correct!
TDWay2 years ago
I could not help but notice the snow, just another word of caution, cold temperatures drastically slows down the curing time and the PVC Cement should never be applied or used below 32 degrees, always read the labels for working temperatures. I'm some what surprised that some of the last joints haven't failed.
al_packer2 years ago
Wrapping the PVC with a couple of layers of 3M Filament tape (the stuff used for packaging) will reduce the danger of shrapnel
Pizzapie5003 years ago
What if your solenoid runs on AC?
It should still work, just fine, I can imagine how it could anyway. Hook it to a 9v battery and see what it does. (It can't hurt it)
Dang it! The solenoid blew up! JK! Yeah it works, it makes that clicky noise.
Good, you actually got me there. Yea, do you have a sprinkler system that uses these which plugs into your outdoor AC, if so then that control box actually adapts the power to lower voltage DC. That may lead to the belief that it is an AC valve, or I don't know what I'm talking about.
kve233 years ago
some kinds of pvc are not for pressure but others are designed for pressure
ghoru5 years ago
Coolest sound ever! lol cant wait to build one...or 2...ah hell go for 3 how big are paint balls... :D
seltzer10 ghoru4 years ago
paintballs come in different sizes but the best to easily fit is the .50" paintballs
3/4 inch pvc barrel
ghoru ghoru5 years ago
hmm... wonder how a 3 barrel separate trigger system would go....?
paul12564 years ago
dose the size of the air chamber matter
YOu used a dwv reduser, this means its not pressure rated a can explode 
matthewbeckler (author)  imthatguy11254 years ago
Thank you for your comment. This is a very real and serious concern, and has been mentioned at least once in my writeup above. I have never had problems with my DWV reducer, but in future designs I will only use pressure-rated fittings as I mentioned in step 2. Thanks for your concern.
 ok sorry I just noticed it in the intro, also you may not want to shoot it in the snow because pvc becomes brittle, for more info you can check www.spudfiles.com

lew00045 years ago
I was wondering if you should make a picture of a End-Around Pneumatic Cannon except with a 3 barrl
matthewbeckler (author)  lew00045 years ago
Part of the design restrictions that come with using the U-shaped valve is that the barrel can't be too large, otherwise it would collide with the pressure chamber. The 1.5" barrel is probably the largest diameter that would work alright with this valve.
what size wood a tennisball need.
matthewbeckler (author)  lew00045 years ago
Spudtech sells 2.5" Schedule 40 PVC that fits tennis balls. I have never purchased any pipe this size, but I've heard of people getting good results.

http://www.spudtech.com/detail.asp?id=38
i'd use shooter marbles as ammo. lots of them. you ever seen what happens when a marble hits a wall at 300 FPS? it explodes. loudly.
You should use some disposable cameras for your firing circuit i bet you could get a pretty good power increase if you try it tell me how it goes
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