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PVC-Caps keep bursting?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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PVC-Caps keep bursting?

Unread postAuthor: VirusX » Tue Oct 27, 2009 1:25 pm

Hi,

Since wie took a smaller barrel for our spud gun, our caps are bursting very often.

This is the smaller barrel (the right one) :

Image

And here are the bursted caps:

ImageImage

The left cap had a piece of wood inside, too.

Do you have any tips for me how I can prevent the bursting of the caps or how to make the aps more solid?

(At the first shots when the cap was still ok, the ammo reached about 220 yards, some people from a 600 yards far apart house came and asked, what's banging so loud :D )
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 27, 2009 1:59 pm

No point in wood reinforcement when the threads are a weak spot, can't you get pressure rated PVC? Failing that, pour in the epoxy ;)
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Unread postAuthor: VirusX » Tue Oct 27, 2009 2:16 pm

jackssmirkingrevenge wrote:No point in wood reinforcement when the threads are a weak spot, can't you get pressure rated PVC? Failing that, pour in the epoxy ;)


Hi,

Sorry I don't understand your first sentence, my english is not good. (Google Translator didn't show me a good translation, too)

Do you mean the piece of wood is too weak so I should better take a harder piee of wood?

In our building centers there are only PVC-pipes of low flammability, are they pressure rated, too?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 27, 2009 2:21 pm

I mean the cap is failing because of the threads where you screw it on, that is the weakest point, so the wood reinforcement is not really enough. You need to use pipe with thicker walls.
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Unread postAuthor: cannon monkey » Tue Oct 27, 2009 2:22 pm

i never worked with pvc caps like this but...
try finding a hard peice of wood and put threads on the wood then just screw the wood plug into place
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Unread postAuthor: VirusX » Tue Oct 27, 2009 2:24 pm

jackssmirkingrevenge wrote:I mean the cap is failing because of the threads where you screw it on, that is the weakest point, so the wood reinforcement is not really enough. You need to use pipe with thicker walls.


This is the thickest cap I can get in a german building store. :(

So how can make this cap more resistent?

Edit: Ah thanks, cannon monkey :wink:
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 27, 2009 2:36 pm

do you need to have the cap removable? if not pouring in some epoxy resin should do the trick, it's what I did here.

Image
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Unread postAuthor: VirusX » Tue Oct 27, 2009 3:01 pm

Yea it has to be removable, we fill in the fuel through this hole.
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Unread postAuthor: ramses » Tue Oct 27, 2009 3:31 pm

you could put the cap in some kind of disposable contariner and then cast epoxy on the outside.

red is epoxy, black the original cap, and green some kind of disposable container.

Make sure that no epoxy can get into the part of the cap with the threads.


I started captioning the picture, but then realized that google translate wouldn't affect it.

or you could buy a metal cap, as long as the threads are the same.
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Unread postAuthor: Technician1002 » Wed Oct 28, 2009 1:02 am

The flat caps in your picture are not built to handle any pressure. They are a dust cap. A cap built to withstand pressue is often domed in shape. I have found ABS to be much less brittle than PVC so it less likely to shatter, but it is softer so it may be more likely to blow off. In places where you can't buy a proper threaded cap a female adaptor with a short length of pipe and a proper glued pressure cap may be the solution. It lengthens the chamber somewhat and appears what Shurshot is using on their cannons.

The cap is a female adaptor, short length of pipe and a cap.
http://www.youtube.com/watch?v=zl-54JdszlE
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Unread postAuthor: VirusX » Wed Oct 28, 2009 9:35 am

Technician1002 wrote:The flat caps in your picture are not built to handle any pressure. They are a dust cap. A cap built to withstand pressue is often domed in shape. I have found ABS to be much less brittle than PVC so it less likely to shatter, but it is softer so it may be more likely to blow off. In places where you can't buy a proper threaded cap a female adaptor with a short length of pipe and a proper glued pressure cap may be the solution. It lengthens the chamber somewhat and appears what Shurshot is using on their cannons.

The cap is a female adaptor, short length of pipe and a cap.
http://www.youtube.com/watch?v=zl-54JdszlE


Hi, sorry but I dont know the technical term "female adaptor" in my language(german), do you have any pictures so I can imagine what you mean?
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 28, 2009 9:43 am

VirusX wrote:I dont know the technical term "female adaptor" in my language(german), do you have any pictures so I can imagine what you mean?


female connector [tech.] die Anschlussbuchse
female connector [tech.] die Aufschraubverschraubung
female connector die Buchse
female connector [tech.] die Buchsenleiste
female connector [tech.] der Buchsensteckverbinder
female connector [tech.] die Gerätesteckdose
female connector [tech.] der Muttersteckverbinder
female coupling [tech.] die Kupplungsdose


One of them must be right ;)
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Unread postAuthor: VirusX » Wed Oct 28, 2009 9:55 am

Hey, I used leo.org, too but all these translations are very general, nothing that really matches to a piece of pipe or spudgun ;) I searched for every word in google images and it was not successfull.

(@Jack, kannst du deutsch? Du hast ja eine deutsche Signatur ;))
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 28, 2009 10:39 am

VirusX wrote:kannst du deutsch? Du hast ja eine deutsche Signatur ;)


No, I just like Rammstein;)
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Unread postAuthor: MRR » Wed Oct 28, 2009 11:32 am

I think I have to help out a little....

Ein "female adaptor" hat bei einer Schraubverbindung das Gewinde immer innen, ergo hat eine "male" eine aussenliegendes Gewinde.

In der Regel kann man sagen....
Female -> weiblich -> ist immer größer
Male -> männlich -> ist immer kleiner und wird in die female geschraubt oder geschoben.

Klingt zwar komisch aber ich habe mir den Mist nicht ausgedacht :wink: .
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