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Pneumatic Pressures: The Safe, The Possible, And The Crazy

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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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Gippeto » Sun Nov 22, 2015 6:33 pm

Delrin block with the shaft pressed in. Curved line is just there to indicate where the undercut is.

Can sort of see the undercut on this one...and the ring on valve body where seal takes place. Seal diameter is not much larger than absolutely necessary, which helps minimize hit required to crack it open.

Image

Was not my idea...Larry Durham (Designer of the USFT rifles built by Tim McMurray) calls it a "toilet plunger" valve stem.
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Brian the brain » Mon Nov 23, 2015 2:37 pm

As usual, Brian's solution is elegant and simple.


:D
Not many people would call me elegant....
My design is actually partially counterbalanced.
I still want the selfclosing element, so it's about 80-90% balanced.

( DAMN!! One more week and I've hit 10 years of SF membership!)
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: mako » Mon Nov 23, 2015 2:49 pm

@gippeto. Okay, that's what I thought. The counter-sunk 'undercut' is quite the innovation, I think. It seems like even a hard plastic (or metal) would work well in that design.

@JSR. I'll have to get my hands on some. How resilient is it? IE, does it recover its shape after being forced against the metal face?

@Brian. LOL. Hey, if the shoe fits, right? Every design I've seen of yours fits the description. ;) I actually noticed the partial counterbalance aspect. That design looks like it would be perfectly customizable for pretty much any balance level you wanted. (Ten years? Wow. Just under two years for me... )
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2015 9:55 pm

Not many people would call me elegant...


How could you say such a thing?

brb.jpg


:D
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Brian the brain » Tue Nov 24, 2015 11:45 am

Notice the purposely un-balanced glasses....

You made my wife LOL JSR....
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: mako » Tue Nov 24, 2015 12:25 pm

The top hat... nice touch... XD
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: jackssmirkingrevenge » Wed Nov 25, 2015 5:39 pm

Notice the purposely un-balanced glasses...


"Elegant" demands Monocle!

You made my wife LOL JSR


Is that a good or bad thing hehehe
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Ragnarok » Sat Nov 28, 2015 10:50 am

jackssmirkingrevenge wrote:Hydraulic fittings are commonly rated to 8,000-10,000 psi, that would be the "sane" limit to me

I'd advise against it. Air starts doing very weird things at those pressures, both in terms of how it interacts with other materials and how it behaves on its own.

A litre of air in that pressure range stores the same kind of energy as a hand grenade (which isn't entirely surprising, as this much air masses more than half a kilo), compressibility deviates significantly from the ideal gas law (it's so dense at this point that it starts acting more like a liquid), you get several of the other problems that can occur in hydraulic plumbing (like hammer effects, where the momentum of the fluid starts presenting an issue), rapid de-pressurisation will cause the air to condense or even sublimate (which could potentially jam valves), you'll have explosive decompression in many materials, potentially cases of embrittlement in others, the reactivity will get all kinds of screwy with that kind of partial pressure of oxygen, etc, etc.

Trying to use air (or, perhaps preferably, pure nitrogen) at that kind of pressure would mean having to do a major research project before you even started designing, and you'd be breaking into areas that aren't all that well documented in this particular context.
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Does that thing kinda look like a big cat to you?
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: mako » Sat Nov 28, 2015 12:01 pm

Is it a bad thing that every single one of your warning points made me go "oh, cool!!"? :D

More seriously, though, I think simply GETTING to 10,000 PSI at all would be a learning experience. By the time you were able to achieve those pressures, you'd have learned a LOT. And the fact that it's uncharted territory... well, just icing on the cake, in my opinion. :wink: Course, if I were to experiment with airguns using those pressures, I'd do 99.99999% of my testing via remote. A small safety room inside a (full) 50,000 gallon water tank might work.
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Gippeto » Sat Nov 28, 2015 9:00 pm

Not so sure about all that. Although 10000psi N2 is not yet readily available everywhere, it is available in some areas (for a price), as are regulators/fittings/valves/hoses rated for it. Booster pumps can be purchased (BIG $$$) to go that high or higher. What can be purchased can certainly be reverse engineered and built. Have built a booster pump, wasn't much of a challenge really.

If running the air rifle at 10000psi proves difficult...throw a regulator in the tube and run the valve at a lower pressure.

Already there are air rifles (both regulated and un regulated) being produced that fill to between 4000-5000psi...10000psi is simply a logical step once availability catches up. Wasn't all that long ago that 4500psi was hard to come by...not so any longer with scba tanks and booster pumps being available and rapidly becoming the norm for those running pcps....at a price of course. :wink:

Considering the price point of some of the higher end airguns these days, the availability of better materials (Ti) and machine tools, it's only a matter of time before someone builds a 10000psi airgun.

Just my .02 :)
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: jackssmirkingrevenge » Tue Dec 01, 2015 8:39 am

it's only a matter of time before someone builds a 10000psi airgun.


:bounce:
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: wyz2285 » Tue Dec 01, 2015 11:15 am

Since this thread is talking about pressure, I got a question.
Bought a crosman 2240 and I thought I could add a chamber to it and use compressed air instead, kind like this mod I found Image. Of course I'n not planning on use 3000 psi as a PCP rifle, only 1000 psi. I have a 22mm OD 2mm walled 314 seamless SS tube lying around, would it be enough?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: jackssmirkingrevenge » Tue Dec 01, 2015 12:50 pm

Should be more than enough, that sort of tubing would be able to take the full 3000 psi safely - the weak point will be your attachment, make sure you have that well designed, otherwise you've made yourself a pneumatic rocket.
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: wyz2285 » Tue Dec 01, 2015 2:10 pm

Not sure if the Crosman valve could handle 3000 PSI since it's originally for c02 cartridges. Might push it to 2000 PSI tho.
Didn't you modded a 1344 somewhere in the past? Couldn't find it.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Re: Pneumatic Pressures: The Safe, The Possible, And The Cra

Unread postAuthor: Gippeto » Tue Dec 01, 2015 3:22 pm

Little calculator for you...http://lassengunsmithing.com/html/CylinderStress.htm

Would suggest that the derived hoop stress at max working pressure be =/< 1/3 of the yield strength of the material.

Useful shot count on such a small reservoir at such low pressure will be...few.

Why not make a proper pcp tube and internals?

Have run Hipacs (device in the your picture) with Crosman valves at 3000psi...need a delrin valve stem as the seal on the factory stem doesn't live long beyond 2000psi.
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