SpudFiles

This is the first gun I am adding to the site!!!
construction includes all 1 in pipe,
2 liter pop bottle as resivoir (they can handle 800 psi before rupture!)
modified ball valve as trigger (I greased the inside so it is smoother)

the gun shoots potatoes that are too small to for in my cannon, I made it out of pipe I had laying around.

I will list a video of the damage soon!

PM me if you live in North East Ohio!

Tell me what you think, and if you want offer up some suggestions or advice.
since I can't get the viewer to work here is the link to my vid!
http://www.youtube.com/watch?v=OnLPP7ZnFEc
[youtube][/youtube]

No pictures? BTW there is no way on gods green earth a 2 liter soda bottle is going to handle 100 psi let alone 800 psi.

jitup wrote:they can handle 800 psi before rupture!

Oh no they can't - where did you get that idea? Don't even think about it.
Soda bottles will usually take a bit over 100 psi before bursting, and not a lot more. As such, with safety margins, they should take no more than 50 psi if you want to be safe.

And I think... there should be pictures.

I called the 1-800 number on bottle, I have had it charged to 150 PSI

jitup wrote:I called the 1-800 number on bottle, I have had it charged to 150 PSI

Don't do it. As a matter of fact, replace that chamber with some pressure rated PVC as soon as you have time. Stop defending the soda bottle...it's lame and dangerous.

Otherwise the cannon seems satisfactory, a longer barrel will give you some significantly better performance.

jitup wrote:I have had it charged to 150 PSI

NO NO NO! 150 psi in those things is an absolute no, you're probably within a whisker of it blowing up in your face.

Seriously DO NOT DO IT. I mean it. If you're given safety advice on these forums, you take it without question. People have been killed by these things.

Those bottles will not take 800 psi - regardless of what they've told you, I know this from painful first hand experience.

If you filled a bottle to 150 psi you might not get a rupture if you left it alone and didn't touch it or bump it against anything. Either way under any circumstances you're putting yourself at great risk with a soda bottle.

This is a good start on a basic pneumatic, you had the right idea with using PVC assuming it is pressure rated, but judging from the pics it's DWV foam pvc that isn't pressure rated. That's not necessarily a bad thing given the relatively low psi you're using, but that soda bottle/tape has got to go. Get some more PVC, preferably pressure rated and you will get a much safer design.

You are making this a dangerous hobby for yourself.

Might I suggest you pick something safer, like "running with scissors"?

That's a little rude don't you think? He's got the right idea on the concepts and it's good that he's being open to constructive criticizism. And heck, if he didn't post this gun he may not have learned pop bottles are not safe, tried to pump it up to 800 psi and blown half his face off. I think the gun shows potential.

Thanks for the input, the pipe is rated for 450 psi, I bought the slightly more expensive stuff. About the bottle, it is not attached w/ the tape, I epoxyed it in. The pae is like a shield. Would it be safe at 90 psi? thats what I usally shoot it at and thats what it is at in the video I will post, or is it a bad Idea ingeneral?

It is not safe at any pressure really. 50 psi that Ragnarok suggested is just such a low pressure that if something happened it is unlikely to cause you harm... Note I said unlikely not impossible. That said I really think you've shown us that you are capable of constucting a decent cannon, you just need to axe the entire pop bottle all together. Pressure rated PVC is cheap man! You could upgrade this cannon for less than $10 without changing the design drastically. Then pumping to 150 psi or even more is no longer a terrrifying safety issue.

As someone who worked in the industry, I can affirm that the 20 oz bottles I used to hydrotest (made for iced tea, not carbonated but with nitrogen in the headspace as a preservative) never - unless obviously defective - failed below 250 psi and rarely failed below 300 psi. Before failure as the pressure increased, the bottle would expand in the manner of a balloon to almost twice its original volume until it ruptured.

Of course this is pure pressure testing, and discounts the possibility of added stress by mishandling the pressurised bottle.

People have been killed by these things

By spudguns, perhaps, but not by exploding PET bottles. It would be unpleasant and could rupture your eardrum, but unless you actually have the bottle shoved down your throat it's highly unlikely to be fatal.

Thanks for the info, before I built the cannon I took the valve stem attached it to the cap, went to my buddies house who has a HPA comressor (into paintball) and we stood way back. Then we let his compressor run and it could not make the bottle rupture at 450 psi. I would never try and shoot this gun over 150 psi. I felt comfortable shooting it at 90 psi because that is the pressure that pop is shipped at. I do not want to come off like a know it all, and I admit I am a noob to the hobby. Seeing your guys reaction to this thread I will probably change the bottle for a 2 inch pvc pipe. do you have any suggestions for what size pipe I should use as the resivoir?

jackssmirkingrevenge wrote:By spudguns, perhaps, but not by exploding PET bottles.

I'm referring to spudguns in general. Poor design and safety has killed and maimed, and as such, safety advice on this site should not be ignored.

I've always see bottles fail well below 200 psi, even the ones for pressurized drinks.At much over 100 psi, a solid knock can cause them to break apart.

Can some one suggest a good length of pipe for the chamber of this gun ?

Also how do I get my youtube video to work on this site!!!!!!