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sealing a burst disk in a tube

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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sealing a burst disk in a tube

Unread postAuthor: JDP12 » Mon Jan 05, 2009 10:08 am

Hey all- It looks like a few other people are working on the same project I am- a cartridge hybrid gun. I saw JSR's design, but i want something that the projectile is the same size as the tube and not smaller.

So i set out to build it.

However I ran into a problem. I'm using aluminum tubing, and i need some way to get a burst disk in there, have it seal.

My first thought was to cut the pipe at a determined point, then heat up one end and expand it to the OD of the tubing, stick a burst disk in there and slide the other end into it.

However, my dilemma with this is twofold- First, I'm not sure about the ability of this design to seal. Second, for some reason I don't think the two pipes will stay together- I'm afraid that they would almost come apart due to the pressure.

So that led me to thinking I'll need a threaded connection somehow- a female threaded tube and a male threaded tube. My only difficulty will be in finding that however.

What are your guys's opinions on something like that? Sealing the burst disk and keeping the cartridge together.
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Re: sealing a burst disk in a tube

Unread postAuthor: starman » Mon Jan 05, 2009 10:24 am

ilovetoblowthingsup wrote:What are your guys's opinions on something like that? Sealing the burst disk and keeping the cartridge together.


Ahhhh and therein lies the eternal challenge doesn't it.

You're going to have to figure a way to get the burst disk on the cartridge to pressure seal up against the permanent opening of the breech. In my mind there's really only 2 ways to accomplish the feat....either a screw fitting like a union or a pressure/rubber seal like a camlock. If you use the camlock method, you'll need to find a way to apply some fairly serious holding power (like the cams on the camlock) againt the seal at the breech.

Add me to the list of people who have been thinking about this.... :wink:
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Unread postAuthor: ALIHISGREAT » Mon Jan 05, 2009 10:31 am

you won't get spectacular performance if the ammo is the same size as the tube because i'm guessing the cartridge won't be too long...

so that combined with the fact you are struggling for burst disc ideas should be persuading you to go for a smaller bore than the cartridge.

and as for ideas for a BD holder... i don't think heating and changing the shape of the pipe will do the pipe any favours in the strength department... i would advise against it....

so the only way i see of getting a BD is to have a BD smaller than the bore... so you would need to epoxy in some threaded fittings or whatever for the holder.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 05, 2009 10:48 am

The solution I had come up with when thinking about this style of cartridge is dispensing with the burst disk and actually epoxying the projectile in place, which I';m sure would work but would probably give inconsistent results.

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Unread postAuthor: starman » Mon Jan 05, 2009 10:58 am

jackssmirkingrevenge wrote:The solution I had come up with when thinking about this style of cartridge is dispensing with the burst disk and actually epoxying the projectile in place, which I';m sure would work but would probably give inconsistent results.


How do you propose to pressurize the tube with that configuration?
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Unread postAuthor: JDP12 » Mon Jan 05, 2009 11:13 am

well another option would be to take JSR's original preloaded cartridge design, and use what he suggested (epoxying a threaded fitting into it) but then leave some space after that for the projectile. So sort of a combination. The disadvantage is that the BD is a smaller diameter than the projectile, so it may limit flow somewhat.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 05, 2009 11:45 am

starman wrote:How do you propose to pressurize the tube with that configuration?


The 6mm tubing fits exactly in the fitting of most pumps that have a cam attachment for the schrader (like on this one) so you could attach it directly, the base would then act as a one way valve.
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Unread postAuthor: john bunsenburner » Mon Jan 05, 2009 11:47 am

look at the little diagram i quickly drew, it is simple but it should work.
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Attachments
burst disc idea.jpg
blue: female thread
black:O-ring
Little red line: Burst disc
red: male thread
burst disc idea.jpg (8.68 KiB) Viewed 706 times
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Unread postAuthor: JDP12 » Mon Jan 05, 2009 4:26 pm

I figured something out- its a combination of two designs- I will post a diagram later
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