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HPA chamber material

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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HPA chamber material

Unread postAuthor: jakethebeast » Sat Jul 10, 2010 1:36 pm

hi!

im starting to make high pressure big-bore airgun, and i have experiense on hpa testing. pressure is going to be around 2000-3000psi, and i need an aluminium or steel pipe that has that kind of pressure capabilities, the chamber is going to be 40mm OD and 30-35mm ID. so, is it carbon steel or something else?
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Unread postAuthor: Technician1002 » Sat Jul 10, 2010 3:11 pm

Malleable iron. An old steel medical oxygen tank is what you are looking for. Do not use brittle high carbon steel. The failure mode is unsafe. Use something built for that pressure in the larger diameters. One member is using a SCUBA tank for the chamber on a golf ball launcher.

Be safe first. Large bore at that pressure doesn't give many second chances to try again. Use the right stuff the first time.
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Unread postAuthor: jakethebeast » Sat Jul 10, 2010 4:20 pm

yeah, need to be sure what is doing :wink:
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Unread postAuthor: Gippeto » Sat Jul 10, 2010 9:31 pm

Have (am) using 1026 DOM, .120" wall, 1.75" od on the co-ax. Hydro tested at 6000psi without problems.

Also using 4130, .875"od @ .65"wall. Hydro tested 6000psi, no problems.

If welding is invovled, keep it low carbon or you'll have to stress relieve the entire piece.
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Unread postAuthor: c11man » Sun Jul 11, 2010 12:02 am

Gippeto wrote:Also using 4130, .875"od @ .65"wall. Hydro tested 6000psi, no problems


hmmm that appears to some extremly thick walls... although i not sure how you put pressure into a pip with a negative ID. i believe you mean .065 wall and that makes me feel a lot better about my chamber which is 1inch OD with the same walls.
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Unread postAuthor: Gippeto » Sun Jul 11, 2010 12:21 am

:lol: It's a challenge. :wink:



My bad...you're right, it's .065" wall. :)
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Unread postAuthor: Technician1002 » Sun Jul 11, 2010 12:44 am

I was warned when ordering pipe to make sure the ID is smaller than the OD other wise the pipe will be delivered inside out.

Thanks for the tip that the ID must be greater than zero. What do they deliver if you specify a negative ID?
:roll:
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 11, 2010 12:47 am

Not very scientific, but a 12 gram CO<sub>2</sub> capsule that will take at least 1,000 psi has a 0.75" O/D and a wall thickness of just 0.028"
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Unread postAuthor: theBOOM » Sun Jul 11, 2010 4:12 am

I'm sure 88 gram co2 cartridges could hold a bit more and give you more chamber volume at the same time, they're about 20 bucks for a pack of 2 :D
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Unread postAuthor: jakethebeast » Sun Jul 11, 2010 7:55 am

im thinking to go to the 1026 DOM, its still on "draving" but i needed to now what to use to calculate how much its going to cost :D . and if i weld the stress relief is not a problem, iv made several hundred knifes and every one is stress reliefed 2-3 times in the forging prosess :wink:
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Unread postAuthor: urgle the danish cow » Sun Jul 11, 2010 8:41 am

i suggest machining out a solid aluminum bar into your air tank for aluminum will not rust and is relatively easy to tool.
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Unread postAuthor: inonickname » Sun Jul 11, 2010 9:53 am

urgle the danish cow wrote:i suggest machining out a solid aluminum bar into your air tank for aluminum will not rust and is relatively easy to tool.


Not really a good idea. There's a good chance his chamber will 60+ cm long in the dimensions hes talking. Making a hole this deep isn't easy, no matter how you go about it. The stock is also more expensive. Just buy some DOM stock.
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Unread postAuthor: jakethebeast » Sun Jul 11, 2010 11:28 am

the consept now is going for 25-35" chamber ja 39" barrel, very long but the caliber is going to be 7.62mm(assault rifle ja long range rifle bullets mayby) and im going to button rifle the barrel my self. i havent build a good pneumatic rifle in very long time so this is going to be the "revenge" for the lost time :D :D . just to keep myself busy im now building .177cal 2-10x pistol piston hybrid thats going to be pretty precise because the good airgun barrel, i just need to machine the breech and build a small and portable filling station. the idea in the station is that lets say we are going to have 10x, i put MAPP gas to sylinder and then pressurise it with shock pump, then i sett the pressure to regulator and start firing :)
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