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Airtight help?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Airtight help?

Unread postAuthor: Pieguy14 » Fri Jan 30, 2009 7:02 pm

Hey guys, I've just recently joined up to Spudfiles.com, and on the internet, I have seen peunamatic air guns, and their air chamber is a soda bottle.

Well, Ive recently made one, and Im having some trouble making the valve connection air tight. Ive tried hot glue = fixed 1 air leak on 1 connection
epoxy syring bottles = OK but not great, no air leak and no connection
and PVC glue = Pretty good, but still not airtight

Does anyone have any ideas on how to fix this?
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Unread postAuthor: tape fist » Fri Jan 30, 2009 7:19 pm

from what i can tell your using a valve from an bike tire so what worked for me is to drill a hole in the bottom of the bottle and then drop the valve in trough the top and try to get it in the hole and then use epoxy to glue the valve to the inside.
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Unread postAuthor: Pieguy14 » Fri Jan 30, 2009 7:37 pm

O rly? Ill try that. But im using a small basket ball pump that runs inside the bottle through a vinyl tubing. I could use an air compressor from a bike, but I dunno where to get those.
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Unread postAuthor: SpudsMcGee » Fri Jan 30, 2009 9:26 pm

Or... you can make a pvc chamber, it safer and easier to do.

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Unread postAuthor: Pieguy14 » Fri Jan 30, 2009 9:55 pm

Ived heard that bottles can reach up to 120 psi. How much can a pvc chamber go up to?
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Unread postAuthor: tape fist » Sun Feb 01, 2009 12:06 am

they can reach up to 120 psi but there not safe,more likely to explode, and like you said they leak.Ive taken my PVC cannon to 250 psi but really depends on what your using and how much its pressure rated for if you want i could give you a list of simple and cheap materials to make an air chamber.
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Unread postAuthor: roboman » Sun Feb 01, 2009 12:32 am

What are you using for your trigger valve?

Pressure ratings all depend on the size of the pipe and the wall thickness. It's printed on the side (unless it's not pressure rated pipe). Usually, 2" Sch. 40 is rated to ~250, and smaller diameter pipe is rated to even higher pressures.

Whatever you do, get rid of that soda bottle. It's going to shrapnel, and I can almost guarantee that one of the shards will embed itself in you. Even wrapping it in duct tape doesn't make it safe.
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Unread postAuthor: inonickname » Sun Feb 01, 2009 1:46 am

I wouldn't use a soda bottle as a spudgun chamber, after a long career in water rocketing I'd know they bloody hurt when they blow up (welding mask = good face guard). It's even more dangerous with spudding, as water rockets have some water in them (omg!?!?!?), which has less inertia (I think that's it) when they decide to rupture, but your chamber would just have air.

If you really need to, some people have used these parts of coke bottle bird feeders, some are pvc meaning you can use solvent weld.
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Unread postAuthor: MrCrowley » Sun Feb 01, 2009 7:58 pm

Remove the waterbottle chamber, use PVC. Problem solved.

Never use a soda bottle chamber, they may take 120PSI for the first few times, but they will fail eventually.
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Unread postAuthor: roboman » Sun Feb 01, 2009 8:07 pm

Also, don't even THINK of using PVC solvent/hot glue/epoxy for connecting a soda bottle to PVC. PVC solvent is meant to chemically weld two pieces of PVC together, and it won't work on anything else. Hot glue can't hold pressure, and depending on how much epoxy you used, it can't either.
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Unread postAuthor: Pieguy14 » Wed Feb 04, 2009 12:55 am

Ok, what Im going to do is just start over, once I am satisfied because only a few leaks remain, and I could easily just start over.

Any Ideas on how to make a PVC chamber connect to the main gun by using a sprinkler valve? Never have seen this done, nor known anyone to do it. If someone could PM me on how to do it, that would be AWESOME. But I am going to work on this cannon in the future.
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Unread postAuthor: Gippeto » Wed Feb 04, 2009 1:20 am

Have a look through the pneumatic showcase. See how others have done it.

Threaded fittings would seem a good way to go. :wink:

Did a quick (very) search, this is the first one I found.

http://www.spudfiles.com/forums/new-spr ... 17014.html

There are many more, have a look. :)
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