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Question for experienced spudders: Is it safe?

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Question for experienced spudders: Is it safe?

Unread postAuthor: skyjive » Thu Nov 26, 2009 4:38 pm

I recently realized that the old helium tank I have lying around would make a great pressure vessel. But as far as I can tell, the helium inside was only at a few atm of pressure, so I wonder how much a tank like this can safely take? I plan to hydro test it before using it for anything, and this raises the question of the water potentially damaging the metal since the inside of the tank isn't designed to contact anything except nonreactive helium. The metal is about 1/10 inch thick, based on a rough measurement of the depth of a preliminary hole I drilled, visible in the picture. I plan to have two holes of slightly larger size on opposite sides of the tank, and tap in 1/4" NPT threads as soon as my tap arrives from McMaster. I realize that will give me little flow, but for my purposes that's ok.

So to summarize, will this take a decent amount of pressure? And will filling it with water be a problem? Thanks.

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Unread postAuthor: sgort87 » Thu Nov 26, 2009 5:22 pm

These are made to take about 200 PSI, but if you feel like hydro testing it, go for it. Filling with water should be okay as long as you drain it and purge the tank a few times. The air from your compressor will have traces of water anyway.

When you finish testing, drain out as much water as possible, fill with air, sit the tank upside-down for about an hour, release all the air while upside-down, then fill, sit for an hour again. and vent once more. This will remove the bulk of the water residue in the tank.

If you are still worried, use an oil instead of water.
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Unread postAuthor: inonickname » Thu Nov 26, 2009 7:46 pm

Or you could swish some thin paint around the inside then set it upside down so it can drip out, leaving a thin layer over the inside of the cylinder. This will help prevent corrosion from water in your compressed air. An epoxy enamel intended for metal would be best for this purpose.

Edit: typo
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Unread postAuthor: Biopyro » Thu Nov 26, 2009 8:08 pm

I have seen them before and I am certain the pressure rating was on it. Around 18 bar IIRC.
I didn't use it because I had nothing to connect it to a normal rig, I don't think it has standard threads, but you could always weld it yourself?
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Unread postAuthor: rp181 » Thu Nov 26, 2009 9:18 pm

I wouldn't weld, I would drill it out, and thread it. The top part is usually much thicker.
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Unread postAuthor: D_Hall » Fri Nov 27, 2009 12:01 pm

Just to add to the confusion, I would NOT simply drill and tap. 1/10th inch is not enough thread to be safe. I'd weld a half-coupling to the tank and drill a port from the coupling.
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Unread postAuthor: psycix » Fri Nov 27, 2009 12:24 pm

Technician1002 uses propane tanks. I think this one is quite similar to those.
I believe he brazes a steel pipe nipple into them. Welding is another option.
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Unread postAuthor: rp181 » Fri Nov 27, 2009 12:38 pm

D_Hall:
A propane tank i threaded had a longer part were the valve goes on, around 3/4" for mine. Im assuming the top of this will be the same.

JBWeld is also very good if properly perpared.
I would go thread+jbweld.
In any case, the first step is remove the valve. Do that, and better suggestions can be made.
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Unread postAuthor: Technician1002 » Sat Nov 28, 2009 6:07 pm

psycix wrote:Technician1002 uses propane tanks. I think this one is quite similar to those.
I believe he brazes a steel pipe nipple into them. Welding is another option.


I used a Freon tank of much the same construction for my competition t shirt launcher. They are too thin to weld. They do braze OK. I use mine up to 100 PSI. They do have a burst disk for overpressure protection.
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Attachments
Bottom brazed.JPG
Disposable Freon tank with 2 inch valve brazed into place.
PICT279.JPG
Helium tanks and Freon tanks are in the same family of construction.
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