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air chamber 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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air chamber help

Unread postAuthor: Major Collins » Sun Jan 02, 2011 7:39 am

OK today i bough a Primus 0.34 liter gas bottle , i was wondering if it i could arc weld a steel half inch fitting on . ive already drilled through the top of the bottle for max air flow.
heres a pic of the bottle i got - just a googled pic

http://www.woodworkforums.com/attachmen ... 101-2-.jpg

oh and how much psi i do you think it would be able to handle ?

and btw JSR if you look at this can you tell me how the blow gun and piston actuation diagrams are going?
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Unread postAuthor: metalmeltr » Sun Jan 02, 2011 1:10 pm

Take a look here
It could be welded if you want.
I took my tank to 300psig.
I would be wary of a welded tank at such pressures.
My tank was just drilled and tapped in the top fitting to 1/4" NPT, could probably be tapped to 3/8" NPT, I don’t think there is enough material for 1/2" NPT.
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Unread postAuthor: Technician1002 » Sun Jan 02, 2011 5:07 pm

Due to the thin metal, I brazed mine. See my Marshmallow Cannon.
I used the short fat one so it is the 1lb bottle. If you get good penetration on the nipple without burning through the thin tank, it should work. I was worried about melting away the thin tank so I used brazing temperatures instead of welding temperature. I used an oxy torch setup.

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Unread postAuthor: metalmeltr » Sun Jan 02, 2011 7:43 pm

If expirienced with a MIG or TIG welder it could be done easily. Even an expirenced oxy fuel operater could weld it.
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Unread postAuthor: Major Collins » Sun Jan 02, 2011 11:26 pm

Well i think im going to be welding but it wont go through because im only welding the very top where it it thickest to reduce chances of burning through.

and i dont think ill be tapping because obviously there inst enough material like (Technician1002 ) you said

fun fact : i use to have once of those bernz o matic tanks ,but it melted becuase it was too close to the top of the tank it just melted through :(

ok 300 psi eh? what would the highest pressure it could be taken too and still be safe?
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Unread postAuthor: Gippeto » Mon Jan 03, 2011 12:02 am

Major Collins wrote:

ok 300 psi eh? what would the highest pressure it could be taken too and still be safe?


Unless you're lucky, and someone's actually tested MORE than one, any answer you get is a guess...nothing more.

Don't trust your safety to someone elses wild ass guess.

If you want to know within reasonable limits...set up a sampling (3 or more) of the things, and do a proper hydrotest on each of them...to failure.

An average of the failure pressures will be a general idea of the strength of the tanks from that manufacturer. Divide the fail pressure by at least 3, and use that as your max fill pressure.
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Unread postAuthor: Lockednloaded » Mon Jan 03, 2011 12:19 am

I believe they have a built in relief valve, what ever that is set to should be your maximum
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Unread postAuthor: Technician1002 » Mon Jan 03, 2011 12:42 am

Just an FYI, the pressure relief valve on those is supposed to remain closed to slightly above 300 PSI so they don't vent and cause a fire hazard on hot days. They will most likely vent if you leave them in a closed car on a hot sunny day as the temperature rises well above 100 F.

As an FYI, when testing tanks, check the bottle for the manufacture of the bottle, not the brand of the propane supplier. In the USA, most tanks are made by Manchester or Worthington.
http://www.mantank.com/
http://www.worthingtoncylinders.com/Home.aspx

Coleman, Bernz-O-Matic, and such do not make tanks.
Most disposable tanks are made by Worthington.
http://www.worthingtoncylinders.com/Products/Propane/Camping-Fuel.aspx

The above link has a link to a PDF with the cylinder specifications.
http://www.worthingtoncylinders.com/Libraries/Propane_Specifications/WPG_Hand_Torch.sflb.ashx The important bits are here;
ALTERNATE COMMON INDUSTRY TERMINOLOGY
FOR THESE CYLINDERS:
PROPANE/MAP-Pro™ OXYGEN
14.1 oz. 1.4 oz.
17 liter 34 liter
1,000 cm3 950 cm3
Empty Propane Empty Oxygen
250 psi 500 psi
DOT 39 NRC DOT 39 NRC
NRT NRT
24 oz. 35.2 oz.
680 gms


If you need pressure, use the Oxygen bottle instead of the Propane. It is rated for 500 PSI instead of 250 PSI.
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