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2000psi safe?

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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2000psi safe?

Unread postAuthor: c19o » Tue Nov 13, 2007 11:13 pm

I'm canceling my project of making the 500psi automatic gun ( for a later date when I have a job) and am going to build a pneumatic ram. It will multiply the 125psi my compressor outputs into 2000psi. My only question is that is it safe to put 2000psi into a 1/2" pipe? Like the kind from your hardware store.
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Unread postAuthor: Killjoy » Tue Nov 13, 2007 11:18 pm

The pipe should take the pressure, (note the word "should) but if you have the option to get some sch80 pipe, I'd take it since paying a little extra for piece of mind is money well spent.

Edit: I just realized that maybe I should actually check the pressure 1/2" steel pipe can take before i start talking. With a safety factor of four your run-of-the-mill sch 40 1/2" hardware store steel pipe should handle up to 3100 psi before it deforms. So hardware store 1/2" steel pipe is fine
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Last edited by Killjoy on Tue Nov 13, 2007 11:23 pm, edited 1 time in total.
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Unread postAuthor: elitesniper » Tue Nov 13, 2007 11:18 pm

2000psi into the tube like staying there or just passing through tthe tube?
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Unread postAuthor: Zen/// » Tue Nov 13, 2007 11:18 pm

What kind of 1/2" pipe? A bit vague :D
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Unread postAuthor: Killjoy » Tue Nov 13, 2007 11:24 pm

I assumed he was talking about 1/2" steel pipe sch 40 since that seems to be standard for most hardware stores.
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Unread postAuthor: Hubb » Tue Nov 13, 2007 11:25 pm

Assuming you are speaking of steel pipe.

Here is a rule to remember:
schedule # times the allowed stress divided by 1000
schedule 40 with 6000 psi steel => 240 psi

Try to find you some hydraulic pipe. It should handle it without difficulty.
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Unread postAuthor: f.c » Tue Nov 13, 2007 11:27 pm

at first i thought you where meaning pvc and i was quite scared for your personal safety. but yes 2000psi in steel pipe seems some what acceptable. ive never heard of a conventional gun using that much pressure though.
can you post a diagram of this ram as i am interested.
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Unread postAuthor: Killjoy » Tue Nov 13, 2007 11:30 pm

Assuming you are speaking of steel pipe.

Here is a rule to remember:
schedule # times the allowed stress divided by 1000
schedule 40 with 6000 psi steel => 240 psi

Try to find you some hydraulic pipe. It should handle it without difficulty.


Uh I'm confused, where did that come from?? Cause I see no mathmatical basis for it.
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Unread postAuthor: Hubb » Tue Nov 13, 2007 11:36 pm

Okay, try using Barlow's Formula.

No gas pipe (the normal that a hardware store will sell) is capable of holding this kind of pressure.
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Unread postAuthor: Killjoy » Tue Nov 13, 2007 11:40 pm

Okay thats waht I was doing, and I'm still coming out way above 240psi, by a couple thousand. The allowed stress (or yield strength) is not 6000 psi for steel, is more like 35000 psi, even for hardware store steel pipe.
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Unread postAuthor: c19o » Wed Nov 14, 2007 12:57 am

Here is the ram design I was thinking of, where the hoses are, there would also be progressively smaller tanks. And probably ball valves on the hoses too so you can control the rams. The blue parts are the check valves and at the top is where you hook up yer air compressor.
Image

Sorry bout the pic I'm too lazy to redraw the whole thing. :oops:
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Unread postAuthor: Hubb » Wed Nov 14, 2007 1:39 am

Killjoy wrote:Okay thats waht I was doing, and I'm still coming out way above 240psi, by a couple thousand. The allowed stress (or yield strength) is not 6000 psi for steel, is more like 35000 psi, even for hardware store steel pipe.


Sorry, I made a typo.

c19o: Here is a link to standard wrought steel pipe (common in a hardware store)

http://www.engineeringtoolbox.com/wrought-steel-pipe-bursting-pressure-d_1123.html

According to that, the working pressure of 1/2" pipe is 1300psi.

It may or may not be higher, but I wouldn't trust it with 2000psi. Try to find you some hydraulic pipe.
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Unread postAuthor: Killjoy » Wed Nov 14, 2007 1:54 am

Ah thats what I figured happened but wasn't sure. If you can't find hydraulic pipe c190, then 1/2" sch80 steel pipe I know will take that kind of pressure no problem.

http://www.engineeringtoolbox.com/wrought-steel-pipe-bursting-pressure%20-d_1123.html

According to that, the working pressure of 1/2" pipe is 1300psi.


Just to point out, but those pressure ratings were calculated with a safety factor of ten, while I was calculating with a safety factor of 4.
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Unread postAuthor: psycix » Wed Nov 14, 2007 4:53 am

Okay but how'd you wanna make a piston handling 2000 psi?
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Unread postAuthor: DYI » Wed Nov 14, 2007 5:08 pm

Your ram diagram is backwards. That ram will reduce output pressure significantly. Also, the multiple rams won't work as well as you think. Even if the first ram outputs 500 psi, that pressure will continually drop as the second ram pushes forward. A single stage ram with a high compression ratio will be easier to build and to calculate figures for.

If you can't figure out how to make a simple pneumatic ram work, I'm slightly worried about you making a 2000 psi pressure vessel. This is some serious pressure you're talking about here, and there is no room for error. If this fails, it could kill you. Be safe, and use tubing rated for more than your working pressure. I hope you don't plan on running the piston through hardware store steel pipe, because it won't seal. You need seamless pipe, and for these pressures that means either SCH 80 steel or SS, or hydraulic tubing.
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