5ft Pneumatic Burst Valve Cannon

[l)ave]

This is my first post on the site and I thought I should start off with a completed project. Here is the most powerful potato gun I have made so far, my pneumatic burst valve cannon.

I designed and built the gun with simplicity, efficiency, and power in mind. I managed to achieve all three of those goals. The cannon is simple in that it has absolutely no moving parts, efficient in that it fires at a consistant power and range, and powerful in that it can put a potato through 1/2" plywood at 45 psi.

Here is a picture looking down the barrel of the gun



Here is a picture looking at the back of the gun (valve, compressor, and schrader)



Here is a picture looking at the front of the gun (barrel and reinforcements)



Here is a damage picture (1/2" plywood punctured from about 20ft away with a potato at 45psi)



I often use three sheets of tinfoil which go off at 45 psi as the burst disk. The most power I have ever gotten out of the gun was a shot using 7 sheets of tinfoil going off at 105psi, this shot fired (angled at 45 degrees) a potato roughly 1/4 of a mile.

Respond, critisize, and if your feeling friendly, compliment.

Thank you

[mopherman]

Looks great, but it might have been a bad idea to choke the flow like that. At that barrel diameter, you would need roughly a 15 foot barrel for an efficient c/b ratio. I'm guessing the barrel is 2" ? If you don't mind choking flow a bit, you could afford a 3' barrel of the same length. I don't mean to bleat on about barrels, but i hate wasting air
BTW, nice damage

[BigJon]

Very nice the damage shot says it all. But if you were to miss i think you would have some pretty angry neighbors

[mark.f]

Nice job, but I would recommend a higher operating pressure. If you have access to an air compressor, a 100-125 PSIG operating pressure usually does well. Simply find a disk that will burst around 100 PSIG, (in a 2" union, I'm guessing you'll need quite a bit of foil, or you could use pop can aluminum), hook up a ball valve and male quick-disconnect, and you're set. Insert disk, hook up compressor line regulated to 125 or so, and open ball-valve to fill and fire. The power potential is much greater if you don't limit yourself to 45 PSIG.

[noob of noobs]

Perhaps you could try a pneumatic triggered burst disk? You could go up to much higher pressures. Plus, then you could fire your gun whenever you please.

[Sparkie]

Nooby alert.
How long does it take to pump up those chambers?
Also don't miss that tree

[ALIHISGREAT]

you know what they say, 'simple things please simple minds' and this is about as simple as they come i would really like to see a huge barrel on this beast you could get some awesome power out of it because of your massive chamber (what volume is it?) other than that i really like it because of its simplicity

[MrCrowley]

All I can say is DYI would be proud

Very nice, though I recommend getting a decent compressor, those 12v ones always crap out and are terribly slow.

For upgrades you could change the tee and eblow sizes a few sizes up and maybe put a 10' golfball barrel on it

[mark.f]

Perhaps you could try a pneumatic triggered burst disk? You could go up to much higher pressures. Plus, then you could fire your gun whenever you please.

You could go up to higher pressures without the triggered burst disks. Just use a compressor or gas tank to dump pressure into the chamber until the disk bursts at whatever pressure it was designed to burst at. If you're really patient, and have nerves of steel, hook up a bike pump and just pump until the disk goes.

The only real benefit you get from a triggered burst disk is convenience, as you can control when the disk blows, without a compressor or gas reservoir to dump pressure into the main chamber.

[DYI]

All I can say is that you must have some pretty damn strong tinfoil. When the SCTBDC was used at low pressure, 8 layers would seldom survive 70 psi, and you claim that 7 survived 105. How do you even make these odd numbered disks (like 3 and 7) in large quantities. It wouldn't exactly be an efficient process...

Also, you're wasting a terrible amount of air here. I recommend either extending the barrel, or going to a 3" bore (and still extending it). Burst disks get enough flow that you can easily use a 3" barrel with a 2" valve (but don't use light projectiles in the 3"). You need to get a video of this thing. Even smaller burst disk guns like this can do some pretty impressive damage with good choice of projectiles.

[mark.f]

Yeah, most burst disks from foil are made in layers of a power of two, like 2 layers, 4 layers, 8 layers, 16 layers, 32 layers, etc... Not that it's impossible to make odd numbered layers of disks, but it's just easier to do 2^n disks, where n is the number of folds.

I think the general consensus is to make a longer barrel. You could extend the 2" barrel with some more 2" pipe and a coupling, and then sleeve a (continuous) length of 1-1/2" SCH-40 or SDR-21/26 inside of that with some duct tape.

[l)ave]

Yeah its not exactly rapid fire....

I am using a 1 1/2" valve not a 2" so there is less surface area exposed on the tinfoil and it ruptures at higher pressures than it would in a 2" union. Also I might just have some strong tinfoil

I cut my layers of tinfoil individualy then stack them up and press them into the union. It is slow but it works fine for me.

I guess improvements in flow and air waste could be made by making a barrel with a larger diameter or putting a new 2" valve on there. Or I could just put like a 20' 1 1/2" barrel on. However I feel that my work on this gun is mostly done, I have another MUCH more powerful gun in the works right now and dont think I will be spending all that much time on this one.

Thank you for your comments.

[DYI]

Well, for lower pressure, your method is fine. Considering that the SCTBDC needs 32 layer disks, and that making the disks from a single sheet of layered foil is stronger than putting multiple premade disks together, this method isn't practical for me.

If you switch to 8 layer disks, you compressor will still be able to burst them, and production will be much faster.

[noob of noobs]

Perhaps you could try a pneumatic triggered burst disk? You could go up to much higher pressures. Plus, then you could fire your gun whenever you please.

You could go up to higher pressures without the triggered burst disks. Just use a compressor or gas tank to dump pressure into the chamber until the disk bursts at whatever pressure it was designed to burst at. If you're really patient, and have nerves of steel, hook up a bike pump and just pump until the disk goes.

The only real benefit you get from a triggered burst disk is convenience, as you can control when the disk blows, without a compressor or gas reservoir to dump pressure into the main chamber.

But in a triggered burst disk device, the external pressure of the disk is higher, making the difference between the disk much smaller. Since the difference in pressures breaks the disk (and that difference is smaller) higher pressures can be added in the chamber, right?

[mark.f]

You could just use a thicker burst disk to use higher pressures in the chamber.