First time building a pvc gun... need advice

[aljaz]

Hi folks!
I am from slovenia (central europe) and i've been looking at this site for some time and i kind of liked the idea of building my own combustion spud gun. Nothing complex, just a starter.

But when i built one (it all looked ok to me at first, you know) the bottom cap blew off once. I thought, this isn't exactly safe, so i'm turning to you guys... I guess you've been 'round the block' when it comes to these things, so...

The thing is, that the things you get here are a bit different than the ones you get in the US... i've only managed to get PVC piping small enough for a spud gun, ABS (here, they don't call it that... don't ask) pipes are only for water supply pipes and you have to buy a truckload of 20meters long, 0.5m radius pipes... like, what ever. Plus, you can't get a cap that screws on, you can only get one that stays put (the rubber fitting holding it in place). You don't even get PVC glue (or cement or whatever)!

So i improvised, drilled a few holes, made a closing system to hold the lid tight and still keep it detachable... I even made a camera flash circuit for the ignition (i'm totaly into electronics), but still... Something MUST HAVE GONE WRONG!

So here are the questions:

pvc is pvc right? and it shouldn't blow up just like that, right? even if it has holes drilled in it (for ignition and stuff)? (and did i mention, our pvc isn't white, it's grey, lol)

if i put a fan in there, it won't get grilled, will it? coz, there's quite some force at the back of the chamber you know...

how tight should the spud fit in the barrel? so it won't get stuck... i don't want any accidents...

should I pay special attention at anything when i test it out dry (empty barrel) and is that even a good idea?

i'm using the gas that goes in lighters (mostly propane and butane) as a fuel. are they to explosive for pvc?

thanks for everything guys! really appreciate it!

PS: what's the time over there? Here, right now it's like 2:26 in the morning (can't sleep). anyways, here are some links to pictures of what you can get here:

http://www.totraplastika.si/
http://www.minerva.si/
http://www.pipelife.com/ (slovenian web page under construction)
mostly the pipes i use (read: that can be used) are sewage pipes!

[TwitchTheAussie]

Mate I dont really know, some of the more learned ones probably would but all I can sy is import some sch40-80 and keep your circuits. It would be a lot safer despite the price.

[n00b]

1.) PVC is usable for spudguns if it has a pressure rating somewhere on it (probably printed on the side of the pipe) however, it will fly apart if not properly primed and glued. I'm not sure where to suggest looking for glue and primer, aside from hardware stores and the pipe suppliers. It seems that EN-1401-1 pipe is sewer pipe without a pressure rating. The closest I could come in standards would be the British BS 3505:1986 standard, dealing with pressure rated pvc pipe.

2.)Chamber fans survive suprisingly well, and can even be left on as the cannon is fired. I suggest using a computer case fan, as they are available in many different sizes.

3.) If you are drilling holes in the pipe, drill through an area where there will be two "layers" of PVC (like where the pipe and fittings overlap) for added strength and safety.

4.)A fresh potato can be cut using the front of the barrel pipe, as the water in the potato will make it slide through the barrel very easily.

5.)A "dry firing" with nothing in the barrel poses no special hazards, just remember to keep your hands away from the hot gases escaping from the end of the barrel. Also, even if nothing is in the barrel, point it away from yourself and other people and animals just in case something is in the barrel.

6.)Propane and butane are fine fuels and are used by most spudgunners, and are safe as long as you don't put oxygen or other reactive gases in the chamber, as this will most likely cause the cannon to explode.

[pyromaniac]

Make sure to prime and cement it very well.

Also don't click the ignition at all while it drying just to see a spark.
( or for any reason)

Also instead of cutting the spud with your barrel you can just have pipe about 3 inches long the size of your barrel and cut it with that.

[aljaz]

Darn, i'll try to upload (or post links to) pictures for you to see what's the best i could get my fingers on. it's really hard to drill where there are two layers, coz i just don't know how to make it possible (lack of choice with parts, really...). And i still can't figure out how to make a closing system for the end cap (no screw-on end caps remember...). Oh, i've done some extra research on pipes on the market in slovenia... there's really not much choice, so i'm left with the standard pvc (let's hope it's pressure rated) and my ingenuity to do sth. Or, in the end, i'm left with an old compressor tank as a chamber 8) and some copper pipe for the barrel.

So i'll be back soon with the pictures and hope we can work something out I realy appreciate the help so far guys! Thanks (i'll certainly add a chamber fan)!

[Redcoat]

my first cannon didnt have a screw on cap at the back but i buried the back into the ground and it worked well and didnt blow off.Shook the ground though.

[TwitchTheAussie]

Do something with metal. Forgot which tpic it was but some guy on another site made a bowling ball mortar out of a steel pipe.

[aljaz]

you guys, you guys!

i just found out that the pipe i have is realy not pvc, although it was sold to me as pvc. it's realy PP (polypropylene) and there's a tiny signature that says:

PP (polypropylene)
RPM (the manufacturer i guess...)
DN 110 (radius)
EN 1451-B (the british standard for presure rated pipes, (B = in buildings))

so, i guess i've got nothing to fear. And also polypropylene in not as fragile (or what's the word... brittle maybe?) as PVC. It won't shatter if the presure is to big. It's also supposed to be a suplement for ABS, because of it's same strength, but better flexibility (it's not rubbery though), and its more durable and doesn't wear down.

Yay for me! 8) so, it's building time i guess! I think i'm gonna go for the closing system i had before (it's quite cool) and also install a chamber fan This is gonna be wicked! And i'll be back with pics soon (when i get the parts and the time to build) probably next week. If you want to see them Thanks again dudes

PS: (what's the average thickness of your pipes? my pipe is about 3mm thick. think it's a little thin? i've seen pics of your pipes like 1cm and more... lol)

[Bubba05]

Yeah you should be rite with that set up mate!!
3mm Is fine u'll be ok.
Build then post pics i wish to see this new type of materials..

Bubba

[spudthug]

polypropylene is pvc isnt it?

[Bubba05]

No PVC is a differnt product! polypropylene is used for reticulation set ups in witch you need a larger diamiter. Its stronger and more flexable. eg. a truck could park on it and it wouldnt crack or smash it would just flex shut. I've never seen it used in a cannon befor but it should be ok?

Bubba

[aljaz]

Dudes!

I just finished my canon (lol, l33t) and i want to upload teh photos, but i donno how to. do i just paste a link or sth?

c ya. photos soon (tomorow)