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question, safe psi of glv pipe

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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question, safe psi of glv pipe

Unread postAuthor: vblock » Sun Jan 16, 2011 8:59 pm

ok guys, so im making a new pnumatic airgun i was wondering what the safe working pressure of 3/4 glv pipe baught at lowes was ?
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Unread postAuthor: Gun Freak » Sun Jan 16, 2011 9:15 pm

1000 psi is pobably a good number. Well beyond what most people use, unless we're talking hybrid.
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Unread postAuthor: saefroch » Mon Jan 17, 2011 11:54 am

3/4" galvanized steel pipe will be good in most everything except a high-mix hybrid or an ETG.
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Unread postAuthor: DYI » Mon Jan 17, 2011 2:35 pm

vblock wrote:ok [sic] guys, so im [sic] making a new pnumatic [sic] airgun i [sic] was wondering what the safe working pressure of 3/4 glv [sic] pipe baught [sic] at lowes [sic] was ?


Loathe as I am to respond to your poorly thought out and atrociously worded query, I have an irrational propensity to provide actual answers to questions, perhaps in the vain hope that *others* might pick up the habit.

Firstly, let's assume the use of a relatively weak, 35KSI (yield) steel. Here's a link to the page where the actual standards for pipe steel can be obtained, if you feel like spending $20.

We know the dimensions of SCH 40 3/4" steel pipe, and can thus determine the yield strength using either the thin-walled approximation, or the formula given here by btrettel. Given the wall thickness / internal diameter ratio (greater than 0.1), the thick-walled formula is more appropriate here, and gives a yield pressure of ~9400 psi. Actual rupture pressure would be significantly higher, but the threads and possible manufacturing problems involving the weld and other factors should also be considered. All told, it would probably be reasonable on the designer's part to assume that the pipe will simply explode at around 10000psi, and begin to plastically deform at half that pressure.

How does that translate to a "safe" working pressure? I've already dealt with the "atrociously worded" part of my complaint against your post in my own subtle way, so now I'll move on to the "poorly thought out" bit: Asking the safe working pressure of a part without detailing how it's being used is like asking how fast a car can go - sure there's an upper limit where drag will rip it apart, but that doesn't do you much good in most practical applications.
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Unread postAuthor: cfb_rolley » Mon Jan 17, 2011 10:27 pm

I'm sorry but I'm going to have to agree with DYI, proper spelling, grammar and questions that are a little less ambiguous are definately appreciated on this forum, and there is a spell check button.

First, find out who manufactures the pipe, and try their website to find information. Next stop is google. Thirdly, try here but give us as much information from your research as you can, because that question was a bit like asking "what's the price of eggs in china?"
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