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All metal pneu design: Your opinion wanted.

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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All metal pneu design: Your opinion wanted.

Unread postAuthor: Deactivated 1 » Wed Oct 18, 2006 3:24 am

I was discussing with a friend recently how I would like to make a smallish all-metal pneumatic gun, which could withstand higher pressures to account for it's size. He suggested I use a spent CO2 canister as the pressure chamber (As in, pump it up with air - no CO2 gas involved) I was thinking of a large threaded canister like the one on the left here:

Image

I am not sure of the actual physical dimensions of this canister but it looks pretty decent. The idea is that one would thread on a Tee adaptor to the threaded end of the canister. Inline with the canister would be a ball valve and barrel, while the other section of the Tee would have a schrader valve. The ball valve would be actuated by a spring mechanism.

Can anyone see anything wrong with this, or do you have any suggestions? The only problem I see is that the thread on the CO2 canister might not be the same as on most Tee adaptors.

Opinions, please.

Thanks.
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Unread postAuthor: GalFisk » Wed Oct 18, 2006 8:33 am

I have a 20oz CO2 tank, I can measure the dimensions if you want.
You'd want to unscrew the valve on the canister (it has much too low flow for a cannon) and screw some kind of adapter into the neck, I don't know what that thread is called but I'm pretty sure it' tapered.
Alternatively you can cut the top off of the valve and keep the treaded part, and attach a coupling to that somehow.
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Unread postAuthor: Deactivated 1 » Wed Oct 18, 2006 8:53 am

Yeah I noticed some sort of plastic flow restrictor inside the brass thread... Regarding the tapered thread, do you mean the thread tapped into the bottle itself? Or on the brass connector? If you know anything about the thread tapped into the bottle itself, any info would be great. Then I could do away with the flow-restricting stock fitting and replace it with something better, assuming I could get a matching thread.

The length and diameter of the cylinder would be great if you have the time, GalFisk.

Edit: For the bottle above, I think the thread at the bottle lip is called "CGA 320"? Hopefully it's possible to get a CGA 320 to 1" male thread adapter...
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Unread postAuthor: )DEMON( » Wed Oct 18, 2006 11:20 am

What co2 regulator is that and how much does it cost?
Can you give me a link to it?

Keep in mind that you want to keep all the liquid co2 in the 20oz or it might spike in your cannon.** Oops, silly me... :oops:

Well in that case I heard that you must only use the gas the cylinder is indended for. Some guy told me that a co2 chamber is only ment for co2 and if you try to put air in it you could make the chamber weak, leading to an explosion. Thats what I was told, I don't know if it is true.
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Last edited by )DEMON( on Wed Oct 18, 2006 2:31 pm, edited 1 time in total.
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Unread postAuthor: drac » Wed Oct 18, 2006 11:22 am

)DEMON(... read.

He suggested I use a spent CO2 canister as the pressure chamber (As in, pump it up with air - no CO2 gas involved)
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Unread postAuthor: Deactivated 1 » Wed Oct 18, 2006 7:00 pm

Okay )DEMON(, I'll have a look into that. I would expect that's just marketing talk to convince people to buy more bottles for each gas they want to store, since in the end there's just a pressure acting from the inside and that's all that matters to the bottle. I'll still check it out thought because I wouldn't want it to explode on me, not that I know how to pump it past 200Psi with a bike pump...

Not sure about the regulator. I just got it off google images, but the cylinder is a "Pure Energy" 20oz container, see here. (I wouldn't need a regulator in this setup anyway)

What can you tell me about the thread that connects to the bottle? I noticed they all seem to have built in valves, which would really suck for fast discharge rates as discussed above. I had a look for replacement threads, but I'm not having a lot of luck as they all have built in flow restricting valves. Do you think it's feasible to drill the centre of them out? I assume its okay to restrict the flow when there is CO2 inside @ thousands of Psi, but for air at 100-200Psi, I think it would severely diminish airflow.
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Unread postAuthor: frankrede » Wed Dec 27, 2006 2:30 am

pressure from co2 is the same as from air so I don't know why it would make it burst, word of warning, its really hard to get the top screwed off,I couldnt get it off even in a vice with a large wrench. You would be better using Pvc.
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