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Brazing kills sharders

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: john bunsenburner » Fri Dec 05, 2008 3:34 pm

But it would not be possible to use pressures of 200bars on them right? What valve could i use instead that works similarly and that is not extremely expensive.
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Unread postAuthor: Ragnarok » Fri Dec 05, 2008 3:43 pm

john bunsenburner wrote:But it would not be possible to use pressures of 200bars on them right?

Certainly not, that would be inconceivable. 20 bar is a lot, 200 is a ridiculous amount, and not to be trifled with.
You certainly shouldn't be using 200 bar if you have to ask questions like that, and I wouldn't even begin to consider it until you have a lot of experience in the 10-30 bar region.

There are things that will handle those pressures, but for your safety, until you've done a lot more research, it would be highly irresponsible for me to endanger your safety by telling you what those things are.
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Unread postAuthor: john bunsenburner » Fri Dec 05, 2008 3:54 pm

Ok, sounds like a good, responsible answer. I am acctually trying to make sure rather than acctually using such pressures. I do not plan to use anythign above 500psi really, simply becaus ei doubt it would be worth the trouble, but i was planing to use bulk tanks with a regulator to fill my chamber, and i was really planing to build a gun that will resist such pressures so that i do not have to build another gun altogether but just have to exchange parts. After rethinking i think i ahve a better way to rephrase my question:


Is a sharder the best valve to use as a fill valve under a pressure of 500psi?
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Unread postAuthor: Ragnarok » Fri Dec 05, 2008 4:05 pm

john bunsenburner wrote:Is a sharder the best valve to use as a fill valve under a pressure of 500psi?

A schrader is a reasonable fill valve, but not the best.

Personally, my choice is a pneumatic quick disconnect and check valve - this is the variety I use, good for 35 bar, and although not very high flow, it's compact, and not too expensive.
That doesn't include the check valve though, which is needed to stop the air rushing back the other way through the plug after the coupling is removed.
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Unread postAuthor: microman171 » Fri Dec 05, 2008 4:32 pm

Ragnarok wrote:Wait... What? You just did...


Yeah, I copy pasted them :-). My dad suggested a restart and seems to have fixed the problem...

I have seen schrader valves used in some nice high pressure situations. I dont know if the brass? on the valve would explode or shear if you over pressureised.

Dont trust me on that point, I have only made plastic spud guns. Hence not much knowledge. I know you can use them in stirup pumps as the check valve.

What type of gun are you makeing?
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Unread postAuthor: john bunsenburner » Sat Dec 06, 2008 2:31 pm

I am making a sniper rifle, with a 8mm 1.20meter alli sleved smoothbore barrel and a fiberglass stock. I am using a piece of iron pipe with two end caps as the chamber, what i need is a fill valve that will survive brazing and that will hold pressures of up to 40bars.
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Unread postAuthor: frankrede » Sat Dec 06, 2008 3:25 pm

john bunsenburner wrote:I am making a sniper rifle, with a 8mm 1.20meter alli sleved smoothbore barrel and a fiberglass stock. I am using a piece of iron pipe with two end caps as the chamber, what i need is a fill valve that will survive brazing and that will hold pressures of up to 40bars.
Why 2 endcaps? how are you going to attach valve+barrel
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Unread postAuthor: john bunsenburner » Sat Dec 06, 2008 3:54 pm

welli ahve two end caps on the iron pipe, then i have two holes in each of them, one for a hose that will lead to the barrel and valve and the other for the fill valve, and the fill valve is wha i need help with now...


P.S. The connections are all brazed(besides of coarse the hose!)
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Unread postAuthor: Fnord » Sat Dec 06, 2008 6:28 pm

I've used a schrader at 900 psi, or 61 BAR. It's being used as a check valve in my high pressure pump.
There was also a schrader on my test hybrid, which was exposed to pressures in the 1000-1200 psi range.

You have to remember that even at 1kpsi, there's only about 20-25 pounds pushing the valve closed.

I like Ragnarok's idea better though, as long as the check valve can handle the pressure.
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Unread postAuthor: john bunsenburner » Sun Dec 07, 2008 3:57 am

Ok thank you for your help, ill order the check valve and the quick connects, today.
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