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I'm gettin some free stuff

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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I'm gettin some free stuff

Unread postAuthor: pretzelperson » Thu Nov 29, 2007 10:51 am

My cousin's step dad works at a factory that uses high pressure steam to run some machines. They are doing some demo work and reconstruction at the place where he works. He is bringing some hardware for me to make a pheumatic. He is bringing me a a piece of pipe and fittings rated to 15,000 psi for air/steam. The pipe is 5" diamater and 4' long. And the other bonus is he is bringing me an old compressor that will compress gas to 17,000 psi. I think I should be able to get some pretty high velocity with such a set up.

I have a couple of questoins. I think I want to shoot batteries: size AA, C and D. I am going to use sch 40 pvc for the barrels because it is pressure rated. How long should I make the barrel? Any other suggestions for ammo that won't blow apart at such high pressures?

Also, in terms of a valve, I'm not sure a sprinkler valve can handle that kind of pressure. Does the sprinkler mods described here increase the max pressure? Should I get some PVC and make some sort of piston type valve? How can I reinforce the PVC to handle the pressure? My cousin's step dad said he could bring a valve he called a QEV that they use in the system, but I'm not sure that would be strong enough. What do you guys think??

Finally, in terms of actually shooting this thing I think it will have a bit of rkick when I release all that pressure, but I'm not sure. Do you think it will be a problem? I wonder if this think will be loud.
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Unread postAuthor: Hotwired » Thu Nov 29, 2007 2:07 pm

o.0

It's actually possible to compress air to 17kpsi?
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Unread postAuthor: paaiyan » Thu Nov 29, 2007 2:31 pm

I think at that point air would liquefy. But lets assume it doesn't. you're going to need something a whole heck of a lot stronger for the barrels. That PVC is only rated to what, 200 PSI tops? Even though it's not the main load-bearing piece, it still will burst if you're suing pressures like 5k. You need a seriously strong pipe for the barrel too.
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Unread postAuthor: Ragnarok » Thu Nov 29, 2007 3:00 pm

Well, I think air can go up to that level, but I'm not sure. Sure as hell wouldn't want to be near it if it went wrong.
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Unread postAuthor: LikimysCrotchus5 » Thu Nov 29, 2007 3:01 pm

Yes definately agreeing with paaiyan. You know you will be the first to be able to reach this pressure? Seriously this is alot. You will break the sound barrier but what mach im not sure.

Batteries can be lethal in aa sense that acid can splash everywhere, hurting the environment and you. Consider other ammo.

This will be super loud. Loud enough to make you permanently def without ear protection. Get some.

Most valves cant handle 17,000 psi especially a sprinkler valve. You can make one with pressure rated metal and sealing face that is capable of 17,000 psi without tearing. Or i would rather go with the QEV.

You could possibly make this into a super awesome catostrophic doom bringing hybrid. If you can get mixes of lets say 100X if possible. But this would be already powerful being a pneumatic.

The kickback, recoil, can be lethal. I suggest mounting it so something that is heavy so that it can take the recoil and reduce it.

The barrel would be at the most length so long you wouldnt have room for it, to get the maximum power out of it. Just use the biggest you can get.

The search tool could have easily answered most of your questions. I suggest you give it a look next time before you make a new post.
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Last edited by LikimysCrotchus5 on Thu Nov 29, 2007 10:03 pm, edited 1 time in total.
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Unread postAuthor: paaiyan » Thu Nov 29, 2007 3:37 pm

My research leads me to believe that 15000 PSI and room temperature are well above oxygens critical point, which means that it would cease to be a gas and instead become a supercritical fluid. That's probably not the best for a cannon, especially since liquid oxygen is an extremely strong oxydizer, obviously. Also, after firing, the gun would get so cold you couldn't touch it for hours probably.

EDIT: Sprinkler valves also can only handle a couple hundred PSI tops. I suggest you just use this stuff to make a hybrid, but go nowhere near the max pressures the pipes can hold. I just want to let you know that if you go to those kids of pressures, any failure could be deadly.
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Last edited by paaiyan on Thu Nov 29, 2007 3:42 pm, edited 1 time in total.
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Unread postAuthor: potatoflinger » Thu Nov 29, 2007 3:41 pm

Definitely go with the qev, but don't exceed the pressure rating of ANY of the parts that you're using. The rating is there for a reason, to protect you.
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Unread postAuthor: MaxuS » Thu Nov 29, 2007 3:42 pm

Its so unfair that only the people with minimum amount of knowledge happen to have access to these awesome materials.

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Unread postAuthor: paaiyan » Thu Nov 29, 2007 3:51 pm

OK, GGDT tells me that with an 85 in barrel, you're looking at 4200 fps. We all know GGDT has issues with gasses pushing projectiles past mach 1, so to be honest, I have no idea what kind of muzzle velocity you'r elooking at. GGDT also warned me about gas liquefaction. I think it's stupid to even think you can possibly get a pneumatic gun to pressures that high safely.
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Unread postAuthor: DYI » Thu Nov 29, 2007 4:31 pm

You will never get over 1600 fps or so with air, without heating it well above room temperature.

I think that your 17kpsi number is flawed. At least the oxygen component would become liquid. I would suggest feeding the compressor helium instead, and limiting the pressure to 6kpsi or so, if the compressor can really do what you say it can.

Let me also say that you do not have the understanding necessary to work safely with that kind of pressure. The valve would have to be custom made, to very high tolerances and with extremely high quality materials. I would suggest steel hydraulic tubing for the barrel.

With a 4" porting piston valve and 4" diameter by 20' long barrel, 6000 psi helium, and a 6 pound projectile, you will be getting muzzle energies and velocities roughly equivalent to those of light artillery pieces - over 300 000 ft/lbs and 1800 fps. I rate the odds of you doing something relatively good with these parts at about 1/200 +/- 50%.
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Unread postAuthor: ALIHISGREAT » Thu Nov 29, 2007 4:34 pm

i think with a pipe that big a high pressure coaxial could be good?
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Unread postAuthor: Biopyro » Thu Nov 29, 2007 4:37 pm

I wouldn't want to be anywhere near air at 17Kpsi, which in terms of hearing damage at 1m is eqivalent to being 160km away from krakatoa (LOUD!), and in terms of shrapnel speed I would guess is approaching that of a grenade.
Also, I don't think the compressor will reach 17k at any great speed

I think your best bet is to get some 22mm copper with 15mm for a barrel and a good old fashioned ball valve. You could probably go up to 600psi safely, and still get some suprisingly good power.
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Unread postAuthor: LikimysCrotchus5 » Thu Nov 29, 2007 5:03 pm

Yea but if he could get a custom piston made to tolerate the pressures he's using and pilot it with a ball valve, performance will be much more than with just a ball valve alone. Make sure, before you start this project, that you get enough research enough about building, welding it and firing it safely so that you know well enough what you are doing.

I like DYI's idea, you should go with that. He knows his high prssures, just look at his recent gun. You'll be impressed, but you could achieve more power, only because you have to resources. Use them wisely.
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Unread postAuthor: potatoflinger » Thu Nov 29, 2007 5:20 pm

Maybe he meant 1,700 PSI compressor instead of 17,000 PSI?
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Unread postAuthor: jrrdw » Thu Nov 29, 2007 5:27 pm

Given that most pneumatics use about from 75psi to 250/300psi, and hybirds are average 400/450psi, why not use the high pessure pump to get 550/600psi. Stronger then hybirds, but not off the charts. A well built piston valve could work well with these kind of pressures, as long as it has a great bumper system. You can use the QEV to vent the piston valve.


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