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Weekend project design.

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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Unread postAuthor: El Chupacabras » Mon Feb 04, 2013 8:33 pm

The factory makes propane tanks. Well now with a measurement of 0.039 I get only 468 psi for the max pressure. Now I'm not only worried but also lost LOL.

What should I do? According to what you have said, welding is not the answer. I find it hard to make threads on the inner part of the absorber, so I can't use the shock absorber as a tank. I don't want to use a fire extinguisher tank because the whole idea is to make something compact, and they are rather bulky. I want to make a portable thing so that I don't need my compressor all the time.

Well I guess I'm gonna have to drop the whole thing off :cry:

Life is tough and then you die.... Anyway thank you for your advice.
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Unread postAuthor: ramses » Mon Feb 04, 2013 10:59 pm

Keep in mind that the material strength for material strength for cheap steel is on the order of 32ksi, not 9ksi like you were using. That said, a lot comes down on how it is welded.
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Unread postAuthor: El Chupacabras » Mon Feb 04, 2013 11:40 pm

I have several issues here:
One, I cant find the correct kind of steel used in the shock absorbers, therefore I can't find the variable to work Barlow's formula for the strength of the "tank".
Two, My skills at math stink to say the least. I might even screw up adding 2+2.
Three, I know for a fact that the shock absorber was welded somewhere in time (I don't pretend to be stubborn) and it can be welded again with the right welding rod and the right welding system.

That said, the reason I chose the shock absorber as a tank was simply common sense. I am an automotive mechanic and I know how much work they have to do when you hit a pot hole. I figured if they can take a hydraulic hit of let's say a pick up truck loaded with a ton of materials when it hits a pot hole on the street, they surely could withstand pumping air inside them up to 500 psi. In fact some of them work with gas inside and you can even raise and lower the car through the absorbers. Back in the 80's "El Caminos" were equipped with those at the factory as I recall.

So after giving it some thought, what I'm gonna do is I'm gonna go ahead and have it welded, and tested for pressure, given that the guy has the proper equipment for the tests. He tells me they test it for over 24 hours. before they give the final OK to the tanks they make there.

Let's see what happens..... To be continued...
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Unread postAuthor: Gippeto » Tue Feb 05, 2013 12:00 am

I think you misunderstand my objection to welding.

My primary objection to welding centers around the lack of serviceability. As a mechanic, I'm sure you've sworn at an engineer or two for making some things so BLOODY hard to service. Injector pumps on the new Ford diesels come immediately to mind....right up against the firewall...you have to R&R the cab and front clip to work on the pump.

My own philosophy is to not use materials of unknown origin. Steel is CHEAP...I would recommend that you buy a piece of seamless tubing with known tensile/yield strengths to use as a starting point.
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Unread postAuthor: jackssmirkingrevenge » Tue Feb 05, 2013 2:21 am

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Unread postAuthor: El Chupacabras » Tue Feb 05, 2013 12:31 pm

Ok guys, I went to the tank factory, and my friend calculated the stress factors and all that for the shock absorbers and they don't pass, so that means you were right Gippeto. He recommended galvanized pipe of about 1 1/2" to 2" with threaded caps. Im going for that.


Those tanks look beautiful Jack, but here where I am located it is a real pain in the butt to get things through the internet.

I'll get the galvanized pipe as soon as I get a chance to go downtown to buy it.
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