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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: Zen/// » Thu Nov 29, 2007 6:29 pm

This will be super loud. Loud enough to make you permanently def with ear protection. Get some.


http://www.makeitlouder.com/Decibel%20Level%20Chart.txt
Loud? you say?
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2007 6:38 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.


It would be loud but not unheard of - think of it this way, your average assault rifle develops 50,000 psi in the chamber, and a tank cannon firing high velocity rounds can go over 85,000 psi.

Even if the figure quoted were correct, it would be overkill for a spudgun by any standards. For a large (1" calibre plus) spudgun, 500 psi is more than enough for unmanagable performance, and even for smaller launchers, 1,000 psi in a well built pneumatic wouldeasily give a higher muzzle energy than a rimfire rifle.
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Unread postAuthor: DYI » Thu Nov 29, 2007 8:14 pm

I also somewhat expect an error in the output pressure for the compressor. I also didn't know before that it was possible to liquify oxygen by pressure alone with no temperature change, but wikipedia and GGDT seem to be united in the belief that you in fact can (damned Mythbusters and their faulty info).
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Unread postAuthor: Ragnarok » Thu Nov 29, 2007 9:55 pm

Any gas can be liquefied by enough pressure.

What JSR says is right - even for my .799 cal 320 psi launcher, the power is very significant. Not uncontrollable, but if I were to use 17,000 psi, I could give a Barret .50 cal a run for it's money, but the sheer mass of gas would create recoil that would physically kill me by ripping my arm off and causing me to bleed to death within a few seconds.

That is uncontrollable. I think no launcher needs to use more than about 500-600 psi, but unless you have serious experience, that should be left well alone. Start with 100 or so, and work up from there as is appropriate for your building skill
Some people will use more than those levels, but they are few and far between.
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Unread postAuthor: miskaman » Thu Nov 29, 2007 10:37 pm

Obviously his numbers are wrong.

1. You would die because at those pressures something is bound to go wrong.
2. Because he's using pipe meant for high pressure steam right? Doesn't steam turn to a solid at a certain pressure?
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Unread postAuthor: Zen/// » Thu Nov 29, 2007 11:03 pm

"Doesn't steam turn to a solid at a certain pressure?"

No. 8) It's called water.

Commercial air guns handle 300-4000psi.

"1. You would die because at those pressures something is bound to go wrong. "

If he doesent use pressure rated pipe, he will be severly injured/die.
A standard pipe that is pressure rated is rated for air, doesent mean you can't use helium, or steam.(pvc+steam= bad idea)
GGDT has steam as a selectable gas.

Just start with lower pressures, then go on from there.
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Unread postAuthor: cwazy1 » Sat Dec 01, 2007 2:12 am

this guy who started this topic hasent posted since his origional post :?
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Unread postAuthor: DYI » Sat Dec 01, 2007 9:37 pm

this guy who started this topic hasent posted since his origional post


15000 PSI and room temperature are well above oxygen's 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 oxidiser


uh oh...


pretzelperson: lets take it to 10k man!!
friend: sweeeeeet!!
friend2: r u shure this is safe?
pp: "of course man"
pp: it can take like, 3x that!
*starts running compressor*
friend: duuuude! its at 8 thousand!!!! thats liek more than a propane tank!
*oxygen begins condensing on chamber walls*
friend2: hey, its goin up faster now.
pp: wtf
*supercritical O2 seaps into valve housings and threaded joints, as well as mixing with various greases and other hydrocarbons inside the old steam pipe*
friend2: its at 10 k
friend: lets go to 15 man!!!
pp: ok...
*oxygen is steadily forced throught various sealing faces and pipe walls*
pp: its ready
friend: lets shoot the neighbours' cat dude!1
pp: yeh!!!!
pp: i cant lift it. help me out guys
*pretzelperson and friends lift cannon, which now has supercritical oxygen dripping from various small leaks*
friend: shoot it!!!
*pretzelperson pulls trigger. projectile, as well as approximately seven kilograms of nitrogen leave barrel at 500 meters per second. Sudden shock causes supercritical O2 to react violently with various materials in the gun*
*massive, earth-shaking explosion*
pp's mom: HOLY S***!!!! WTF WAS THAT!!??!!1? * CRACK* *hit by chunk of supersonic shrapnel, falls to ground*

news reporter: apparently the 53 local casualties from shrapnel wounds, structural damage, and heart attacks today were the result of an accident involving a homemade device called a "potato gun", which exploded when an innocent teen tried to shoot it...


possibly slightly( :roll: ) exaggerated, but you get the point
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Unread postAuthor: potatoflinger » Sat Dec 01, 2007 9:58 pm

^ lol, that was funny, but yeah, I don't think that the person is going to come back. He probably realized how ridiculous his claims were.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 10:57 pm

Even if you are able to bring it that high Dont.Its suicide bring it to 1000-2000 that should be safe
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Unread postAuthor: Ragnarok » Sat Dec 01, 2007 11:35 pm

bigbob12345 wrote:Even if you are able to bring it that high Dont.Its suicide bring it to 1000-2000 that should be safe

You seem to have too many zeros there. Inexperienced people shouldn't even consider using outside 100-200.
I wouldn't go close to 1000, let alone above it - I can think of only one person who's doing it, and some other's who are speculating about it.

Talking about too many zeros: Concerned
Possibly the funniest webcomic I have ever read. It took a while to get going, and it's now finished, but regardless of whether or not you have ever played Half Life 2, it's sensational. (A basic knowledge of Half Life 1 and other some well known games helps though)
I really recommend you read it from the start (so you'll need to go there, it's pointed at #21 right now) - it takes a few comics to get going, but some of the later comics practically had me rolling on the floor.
If you don't like it, I personally guarantee I will come round your house and beat you with a big stick.


...and that's why the lines on the road are yellow*... No, wait, I mean that's why there are so many explosive barrels in games.

*A reference to Ctrl+Alt+Delete Comic, the first webcomic I ever read, one of the common "Two Gamers on a Couch" type comics.
It's still good, but contains some references to maturer subject matter, so I'm not linking direct. Use Google to find it if you're interested.
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Unread postAuthor: POLAND_SPUD » Sat Dec 01, 2007 11:59 pm

ragnarok thx it's good someone mentioned that... i've noticed that a lot of people here that want to use > 1000 psi pressures... and usually they haven't used more than 300 psi yet... :shock:

BTW GGDT shows that you can improve performance greatly with if you use steam.... has anyone tried that ?
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Unread postAuthor: Ragnarok » Sun Dec 02, 2007 9:55 am

POLAND_SPUD wrote:BTW GGDT shows that you can improve performance greatly with if you use steam.... has anyone tried that ?

It has been done a couple of times.

The reason it works better is the heat and lighter particles create a much higher speed of sound in the gas than in air.
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Unread postAuthor: POLAND_SPUD » Sun Dec 02, 2007 10:41 am

yeah that is why people use helium or hydrogene... but I want to know how they do it (how they use steam in spudguns).
GGDT shows ~ 30% power increase with steam... so it's interesting.... and seems more practical and reasonable than 3000 psi spudguns
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Unread postAuthor: pretzelperson » Mon Dec 03, 2007 3:40 pm

Holy Crap. Turns out the pipe was for liquid hydrolics. But the pump pumps a ton of air-- Will pump about 5000 psi - air and the fittings I got are great. I hooked this thing up to my oxygen bottle pneumatic and pumped it up to 600 psi. All of the fittings on that thing are rated for a lot of pressure. the bottle is rated for 2200 psi. the weak point is the ball valve rated for 600 psi. I took off my little pressure gauge and added a steel pipe barrel that is 10 feet long. Holy Crap. This thing is unbelievable. The sound. OMG the sound. I though a fricken black powder cannon when off in my garage when I shot that thing. Good thing I was wearing ear plugs. The shock wave from the sound was amazing. Anyhow . . . I launched a chunk of steel bar that was about 6" long and about 1.5" dia. I guess it weighed a couple of pounds. I never saw it and I couldn't find it. You should have seen the neighbors. They all came running out of thier houses to see what was going on. They were very upset--especially the people behind my house. Fortunately most of the people in my suburban neighborhood are pretty cool about this kind of stuff.

I got a QEV rated that will easily handle 5000 psi and some high pressure pipe that will be sweet. I think I will easily be able to launch at 5000 psi once I get this thing put together. Not the 17000 I originally though, but still pretty amazing.
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