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Large pneu. cannon help

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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Large pneu. cannon help

Unread postAuthor: brogdenlaxmiddie » Wed Dec 26, 2007 2:59 pm

Hello!-
What would the best release system be for a cannon with 2 8'x4" chambers and a 2" barrel? Currently, i have a large bronze ball valve. I was going to fit a piece of 3' copper pipe to the handle so that I would be able to open it faster. Please help me by telling me what I should do for this to be the best gun it can be. My goal is to break the sound barrier (hopefully) and to all around make one helluva boom. Please also describe how to/buy these different valve systems. Thanks a lot for looking and helping!
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Unread postAuthor: th3p0p0 » Wed Dec 26, 2007 3:01 pm

is this your first gun? and how big is the ball valve? (like 2"-3")? if its that big and this is your first id stay with the ball valve.
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Unread postAuthor: c19o » Wed Dec 26, 2007 3:11 pm

Yea, I would stay with the ball valve for now too. Then research on how piston valves work, what materials you can use that you can get easily, and all that good stuff. Plan it all out before you spend alot of cash on a big valve to save you the trouble of buying parts again if you mess up. ( like I did :wink: )
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Unread postAuthor: jackssmirkingrevenge » Wed Dec 26, 2007 3:13 pm

If you're not willing to make your own piston valve, for less than $100 you can get yourself one of these, otherwise you can try your luck looking for a 2 or 3 inch solenoid valve on ebay or similar.

By the way, how long is your barrel going to be? Because one 8' length of 4" tubing is more than enough, unless you're planning on a barrel longer than your house.
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Unread postAuthor: Fnord » Wed Dec 26, 2007 3:18 pm

Some options:

Burst disk: a piece of metal or plastic foil placed in a union- most powerful, efficient and easy-to-use valve, but the disk is destroyed on each shot and needs replacing.

Piston valve: Easy to operate, but you have to either build it yourself, or buy one from bcarms or sgort. They aren't cheap, but you get what you pay for.

Spring/pneumatically actuated ball valve: using a spring or pneumatic ram to open the valve faster than you can by hand. You can convert your current ball valve to open like this.

Large sprinkler valve: costs around $50 + for a 2" one, but it's easier than making a piston valve.

You can find info for all of these by clicking the wiki button at the top of the page. (well, maybe not the ball valve one, but we can help you come up with designs if you want to do this)
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Unread postAuthor: psycix » Wed Dec 26, 2007 4:00 pm

I would defenitly go with a piston valve.
If this is your 1st cannon I recommend to make a smaller one (medium size) pneumatic first to get the touch of it.
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Unread postAuthor: MaxuS » Wed Dec 26, 2007 4:57 pm

You are most certainly not going to break the sound barrier with a ball valve, no matter how large it is.

Edit: As far as I know, you can only do it with Hybrids, and as a beginner project, I wouldn't advise building one.
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Unread postAuthor: DYI » Wed Dec 26, 2007 5:47 pm

You can break the sound barrier with air, if you have enough power.

To explain: A volume of gas cannot expand faster than the speed of its individual particles. At room temperature, particles in air average ~500 m/s, which is well over the speed of sound. However, as the expanding air reaches Mach 1, shockwaves will form on any imperfections on the valve and barrel, reducing the expansion speed.

There are several ways to circumvent this problem, and I will explain them all here, from most difficult, to easiest.
1. Somehow achieve a valve with a frictionless inside, as well as a frictionless barrel which is evacuated of air before the shot (which requires a vacuum pump). Can't get more than 500 m/s.
2. Ye Olde Plasma Rifle; Turn the gas into a plasma by heating with extremely large electrical discharge in the chamber. According to one resident genius, could conceivably achieve velocity in excess of 7 km/s if aided by magnets to guide and concentrate the plasma. Not recommended for beginners (or anyone, really).
3. Use massive amounts of pressure, and a very fast valve, to solve the problem by brute force like the AirForce Condor air rifle. Still can't pass the 500 m/s limit though.
4. Heat the gas, either by shock compressing it with a piston, or by increasing the chamber temperature with a heating apparatus. The heat achieved must be very significant to add any meaningful performance. (Several hundreds of degrees fahrenheit above room temp.)
Velocity is limited by the heat achieved.
5. Build a hybrid. The particle speed in the post-combustion chamber is about 3000 ft/s in most cases.
6. By far the simplest of them all: Use a gas with a higher particle speed than air, such as helium or hydrogen (helium is a better choice for a beginner, as using hydrogen has loads of inherent dangers). The speed of sound problem will not be encountered in helium until about Mach 3, and not in hydrogen until ~Mach 3.8. Requires no heating, no evacuated bore, no specialist valve design, and no complex gas mixing.

If you use 150 psi helium, assuming the chamber size that you specified, and a spring loaded 2" ball valve with a 25ms opening time (easily achievable), you could propel a 50 gram projectile at 1325 ft/s (well over Mach 1) with a 20' long 2" barrel. If you use a 2" porting piston valve, you could get a 50 gram projectile well over the sound barrier with a barrel only 10' long. If you use a burst disk valve system with 2" porting, you would only need an 8' barrel (and a 20' barrel could get a 100 gram projectile over 1200 ft/s).

You should go for it. You can buy a suitable multi-gas regulator from McMaster for any pressure you want, and you can buy a CGA adapter (for the tank) from several different sites that can be found simply by searching the term "CGA 580 adapter". I wish you luck, and hope to see another supersonic cannon on Spudfiles (my 2500 fps ball bearing gun is well on the way :twisted: )
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Unread postAuthor: MaxuS » Wed Dec 26, 2007 5:51 pm

Well DYI, you've just made me eat my words..
But as far as a beginner project goes, the Sound Barrier is a big goal.
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Unread postAuthor: DYI » Wed Dec 26, 2007 6:03 pm

I agree there. If I could get a 500 psi helium supply for the SCTBDC (which was actually only my third pneumatic), it could break the sound barrier easily with a 100 gram projectile. GGDT shows that it could do it in its current state with a 40 gram projectile, but I doubt that due to the aforementioned shock wave problem, and the SCTBDC's conspicuous lack of either a frictionless bore or extremely high pressures.
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Last edited by DYI on Wed Dec 26, 2007 8:39 pm, edited 1 time in total.
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Unread postAuthor: brogdenlaxmiddie » Wed Dec 26, 2007 6:40 pm

Joel (spudtech.com guy) has a gun he made that was apx. 5 feet for chamber-4" and a 12' barrel-2" that he claims broke the sound barrier w/o any special gases. However, he was using a supah-valve +. Its a shames he's selling the company cuz then i could just order a supah-valve + from him... oh well.. But thanks everyone for helping! btw- its a 12' barrel and this isnt my first gun. I started with combustion and built 5 guns ranging from 4' length to over 10' but i have built a smaller 3' pnue gun for my best friend which works rather well w. only a ball valve however it was plastic. The new big one i have now is as i stated previously, bronze and much better.
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Unread postAuthor: DYI » Wed Dec 26, 2007 6:50 pm

Joel can claim whatever he likes, but I can assure you, unless you are using the kind of pressure that is unsafe for any PVC pipe, you're going to need those "special gases".

Helium wouldn't be that much work, but if you insist on using a ball valve, you're going to need a longer barrel to get anything of any useful mass over Mach 1. Build a simple barrel sealing piston valve in a 3" tee, with 2" barrel porting, and you could get easily get a saboted golfball at least slightly over Mach 1 (for a grand total of 3300 ft/lbs of muzzle energy).

I highly doubt Joel's claim, because with his setup, even with an incredibly good burst disk system (faster than any piston valve, Supah or not), he couldn't even accelerate the miniscule mass of 20 grams over Mach 1 with air. Now, if he'd have been using helium (which I thought he was?), it would be a different story.
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Unread postAuthor: carter » Wed Dec 26, 2007 7:06 pm

you'll be surprised at the power that you will get. don't get bogged down about the sound barrier. just get some skills and have some fun. DYI that was a good answer and covered everything. i currently have a ball valve on my marble gun. that has a 2''x14'' chamber and 50''x1/2'' barrel and i can't see the marble after it leaves the barrel. i was surprised at that. what i'm trying to say is that you will be surprised at what you will get under the sound barrier.
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Unread postAuthor: DYI » Wed Dec 26, 2007 7:16 pm

For most of our purposes, the sound barrier is nothing important.

The damage done by a massive subsonic round is great fun, and far easier to achieve. I can achieve 6000+ ft/lbs with the SCTBDC, and you can destroy quite a bit with that kind of power. Concentrated on a dart, you can shoot through some pretty strong stuff too.

But this entire hobby is rather short on practical and useful finished products anyway, so you may as well shoot for the sound barrier if that's your goal.
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Unread postAuthor: brogdenlaxmiddie » Wed Dec 26, 2007 7:46 pm

Good response (: what could you recomend then for the loudest noise I can make? DYI- you have been a very awsome help! JW, what is it that you do for a living? You seem extreamly intelligent...
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