So you have a decent sized vacant lot of land (be it farm country, woods, tundra, ice shelf) and you think to yourself, "Hmm...I wonder just how far I can hurl stuff, maybe even into the next county." Or maybe you just like the idea of kinetic energies ten times that of a 50 cal bullet shot out of a sniper rifle. Or maybe you want to get into Punkin' Chunkin'. Well, my friends, you just might want a piston-valve pneumatic cannon.

It'll sure beat the pants out of your neighbor's ball valve pneumatic or hairspray combustion cannon.

Update 2014 - We were young and stupid when my friend and I first built this cannon. We made a lot of mistakes and a lot of safety oversights. I highly suggest reading up on modern potato cannon theory and design before delving into a project of this magnitude. Use your head!

Videos of the recent 2in valve:

Three test shots at 40psi, two with paper towel, the last one with a whiffle ball bat. We were gonna move on to damage shots, but it got dark. I should have damage vids up today or tomorrow.

Videos of the old Mk IV 3in valve:

Preparing for launch, I couldn't find the rocket. So I put in a can of lemonade instead. "There's the rocket!" refers to my sudden realization that the rocket was in the barrel the whole time. Rocket, lemonade, and wadding all shot out over 120 m.

My cannon has a record distance of 1900 feet (using Google Earth along with terrain mapping - it happened to land right between two distinct knolls that I could see from GE). That was a 70 psi shot with a 2.5in x 20ft barrel that was so long it needed it's own suspension system.

I have a video of that shot somewhere but I have it find it I'll post it as soon as I do. That was also the shot that broke the cleanout cap.

During the testing phases, the cannon was barely charged halfway, so I could get away with plugging my ears. I make sure to grab hearing protection for anything 65+ psi.

For these two shots we had an audience.

They were thoroughly impressed:

This shot, something caused the piston not to actuate, and we had a dud. They weren't as impressed :-P:

Step 1: Story Time!! (aka Theory)

So over the past two summers my friend and I have been working on my brainchild: a 3" porting piston cannon. Porting is the spudding term for the size at the greatest restriction between the pressure chamber and the barrel. The air can only move as much through the barrel as it does through the porting (usually the valve) so if you want more air to hit the projectile, you need a bigger porting.

Piston valves work on a principle similar to a plug in a drain. Pressure on one side of the piston, causes the other side, or sealing surface, to make a seal against the barrel, the porting. This keeps the rest of the air in the chamber from escaping. The region behind the piston, called the pilot, is dumped to ambient pressure, and the pressure difference from the valve causes the piston to get shot back quite forcefully. The porting is now wide open, and the air from the pressure chamber rushes into the barrel, launching the projectile.

Sounds fairly straightforward, right? We thought so. Many people had already build 2" porting valves with little trouble, but I wanted to go bigger. One would think that you could just change the size of the parts from 2" to 3" and voila, you have a bigger valve. Well, yes and no. Moving up to 3" increases the size of the sealing surface by 50% or more, and achieving the right seal can prove frustrating, difficult, and expensive.

So, to save you from some of my mistakes, I present you with two, count 'em, two different designs. One is the 2" porting, which still had quite a kick, and the 3" porting valve I used on my cannon, for those of you with higher levels of patience.

1. Under Load: The valve pressurizes from the pilot end, pushing the piston against the sealing surface. The pressure equalizes between the pilot volume and the chamber. Because the surface area on the back side of the piston is larger than the surface area on the opposing size, the force pushing the valve forward will always be greater.

2. The pilot valve is opened. The pressure behind the piston drops quickly, not allowing the chamber side time to equalize. The force pushing the piston forward drops, while the force pushing the piston back remains nearly constant. The two force equal and then...

3. Actuation. The force pushing the piston back exceeds the force pushing it forward, and the valve opens, allowing the air from the chamber to flow into the barrel.

<blockquote>Man my hats off to you! I read about your cannon while looking for info to research a DIY small caliber (about one or two inches) HARP type gun. Not for a weapon but for fun and research. Also I need to motivate myself to build a cannon of some as yet unknown design as large as funds allow. The cannon projectile would be a 2 or so inch composite solid fueled rocket, probably using high powered model rocketry motors for reliability etc. I would use paper, plastic and similar material rocket for safety in the event of an launch failure, IF it could survive the violent takeoff. Maybe gasoline or a low explosive could be used for primary propellant? Anyway after the rocket was fired its rocket motor would ignite before the spin stabilized projectile begins its ballistic arch. Maybe after proof of concept that such a thing could work, the rocket projectile could be staged to gain more attitude? Balloons have served as launch platforms and they work well. I watched a Utube weather balloon rocket launch while sitting above the earth at a claimed 70,000 ft.! Balloons are cool but I just like big guns and the thunders roar and booms that shake my insides with waves of concession lol! Anyone have ideas or a used cannon, ha ha? I'm gonna do it...only being safe and limited funds will slow my progress..... <br></blockquote>
ive seen punkin chunkin with high pressure... how about trying a vacuum cannon... could you hit the magic mile with that?
This is a beautiful thing...............just beautiful.......... <br> <br> <br> <br> <br>5 of 5 <br>
i might use steel pipe for my 4&quot; val.much better under pressure.
I don't understand where everything goes. I understand how they work and the concept, but could you please label the &quot;bulkhead&quot;. I am building one myself and most likely will use this design.
The bulkhead is the part that connects the front side of the valve to the barrel. I haven't really worked on this project in a long time, and there are parts of it that need to be re-engineered, and I can't remember right now if the whole design is optimized. I would go to www.spudfiles.com and look up some designs and get a feel for valve design.
Hey, thanks a ton! I think I've got the jist of it, but I might have some more questions when I start to build it. (My partner is away for a couple of months.)
is that valve 2in???
Yeah, that's the two inch valve. Sorry, I really haven't touched this project in a while, it would take me a while to get everything back up to speed. I would go to www.spudfiles.com and read up on the general mechanics of piston valves if you are unsure - they are rather tricky to make.
What did you use as your rocket, and or how did you build it? (not that it would matter to me, since I would be firing it out into the water, but just to settle my curiousity)
The rocket was made out of PVC.
Could you please add pictures here. That would be very helpful. I'm lost :(
&nbsp;This looks really cool, are you a member on www.spudfiles.com, the only problem I see is that most of your parts are DWV, &nbsp;your piston looks great, my piston on my golfball gun was just a coupler
Yeah, I&nbsp;am, and yeah, I&nbsp;know. XD. That's part of the reason the valve exploded.<br />
&nbsp;Whats your username, arte you still active
I haven't been on there in years, but I&nbsp;believe it is deusxmachina.<br />
&nbsp;You should return, theres a ton of new ideas floating around you probably missed
I might. I'm just super busy a lot of the time. But thanks for the tip! :)<br />
&nbsp;No Problem, Im clemsonguy1125 there to by the way
where you able to get a 4in rubber O-ring at the store or did you have to order it online also who much did it cost and under what section in the store would it be found in? (plumbing, piping, exc, exc...)<br />
Hmmm....I actually don't remember. It might have been custom-made, there are make-your-own O-ring kits that basically give you a piece of rubber that you cut to size and glue together. You can also get them online, try McMaster-Carr. <br />
It would be pretty much impossible to build a pumpkin-capable canon out of PVC.....Well, it is possible but either the pumpkin wouldn't move or the whole thing would explode.<br />
Suggestion: 1 Find a tree 2 Point this straight at it 3 Launch a fire poker at it
how far will it shoot a bottle?
"Three 2"x1/4" steel nipples" ROFL, he said steel nipples! great instructable btw
It's called nipples.
ye i know (i laugh at 'nuts' occasionaly aswell) haha
How destructive is this to the projectile? I have a (slightly larger than) GI Joe type of Radio Controlled parachutest and 800 acres of field. Think load fire fly back to base, do over...
Radio Range over 1500 feet. Skydiver weighs a touch over 3 pounds ready to fly. I have not tried to see what size barrel would be needed, maybe a 3 inch. i would think electronics would hold up okay everything is enclosed inside the resin skydiver body.
Depends on how good your electronics are. As long as they're decently hardy<sub> it should survive just fine. However, if your parachute didn't deploy, well, you're screwed. Also, take note of your radio range. </sub><br/>
sweet! affordable heavy artillary! time to bombard the enemy tank collum(how accurate is this thing)
Not terribly, although with finned projectiles you can see on the map that they all landed pretty much in a straight line. My friend jokes about having a contingency plan which consists of shooting black powder chargers with a safety fuse, just for the nice aerial blast. I told him sure thing as soon as terrorists invade Upstate New York. I'm dying to get footage of soda cans shot at 3/4" plywood, but it has been raining all weekend.
why stop there?put a WHOLE LOTA little steel balls or somthing, a giant shotgun. and then a large steel cone get the idea?
Redneck Deer Hunting.......
what psi can you pump it up to?
The highest we have taken it up to is 90 PSI. The maximum theoretical pressure it can handle is 125 PSI but that prospect is quite frightening. Hopefully before the cold sets in we will get to bring it up to that high and remote fire from 100 ft away.
Upstate New York you say? war time!!!! Crap, my wallet is almost empty....
even if not very accurate still god for area bombardment and area denial
Get damage footage! It looks impressive, but seeing the projectiles hitting stuff really sells it.
Not to bring shame on you but you used Dwv fittings such at the wye and one of the bushings. Dwv = not pressure rated = Shrapnel.<br/>
Uhh, duh? Did you read the instructable? The whole reason the 3in valve failed is because it was DWV. And DWV does work for pressure as long as it has a pressure rating on it. Most of my pipe says DWV ###PSI.
Build one out of copper pipe scraps.... find a Good hearted plumber for donations...... It would look and work GREAT I'm sure....
This design is almost identically shaped to my hip-fired much smaller version. I'd not seen a barrel-over-storage design so I built mine on a whim...yours looks to be much more powerful though. Only thing I can suggest is for your 3" piston, put a spring, or something spongy behind it so it doesnt obliterate the endcap at higher pressures.
I did...it makes absolutely no difference.
How about a tennis ball or 2 for cushion? Also I used to have a potato cannon and we used 2 1/2" electrical conduit for the barrel. A tennis ball fits nice and snug. 4" chamber with some PVC cleaner and ignitor.... Tennis ball out site!!!!
Perhaps some sacrificial styrofoam (insulation kind, not the cheap bead-polystyrene) that takes up 2/3 of where the piston has to travel, that stuff would crush very little, but still give some support....or you're doomed.
Why not use a butterfly valve? I thought the pumpkin chuckers used them, not this porting stuff.
A Really big Ball valve will also work..... You want as little restriction as possible.
Butterfly valves are slower than piston valves. Punkin Chunkers can get away with using them because they are usually mechanically actuated and the reservoirs are several cubic meters. Additionally, the barrels are several times longer. That means a slower actuation time does not make much of a difference in muzzle velocity, but even at my scale, it matters. And butterfly valves and parts and barrels and chambers that go with are are metal, which costs tons of money.
I see, It sounds complex but I shall study it again. Thanks

About This Instructable




Bio: My goal in life is to be a chemistry professor, because a) I've had lots of awesome influential teachers b)Bill Nye kicks ass ... More »
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