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Dive Tank Holding area

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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Dive Tank Holding area

Unread postAuthor: caspar97 » Thu Jul 15, 2010 3:38 pm

I was talking with some friends and we had this idea. What would happen if we used a dive tank as a mobile re-filler. A dive tank can hold lots of pressure and would be great for multiple shots. Off of the dive tank there would be a step-down regulator (or else you would get 1000+ psi rushing into your chamber), then a ball valve. Off of the ball valve would be an air hose leading to your gun and into an air hose connector. Open the ball valve to fill your gun, close to stop. You could do many different things and variations with this, and it is very cheap to get a dive tank refilled with compressed air. One would only have to buy the tank and step down regulator. Any tips, thoughts and comments are welcome, and so are things that put holes in this idea. :)


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Unread postAuthor: jrrdw » Thu Jul 15, 2010 3:52 pm

Sounds like a working idea, hows the cost on the tank and regulator?
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Unread postAuthor: c11man » Thu Jul 15, 2010 4:29 pm

certaily not a new idea but its the cost of a tank and reg that prevent more people from doing this. it would be like using a paintball HPA tank except much bigger. an alteranative to a regulator would be a low flow needle valve. much cheeper but if you dont have a popoff on your gun you could over pressurize if you dont pay attention. also its not 1000psi its somewere in the range of 4500psi
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 15, 2010 4:55 pm

I have a SCUBA tank which I use to fill my commercially bought air rifles, as well as my paintball tanks, works a treat as long as you can afford the initial financial outlay and there's a refilling station nearby.
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Unread postAuthor: Clarke » Thu Jul 15, 2010 5:40 pm

You should be able to hire a tank around your area if you dont want to spend extra.
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Unread postAuthor: caspar97 » Thu Jul 15, 2010 8:47 pm

Luckily for me, money is not a problem and i have a refilling station nearby. My friends are thinking of making a cannon similar to the one here http://www.instructables.com/id/Colossal-Cannon%3a-Building-a-behemoth-piston-valved/ tips greatly appreciated as always, and yes i no that it is not a new idea[/url]
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Unread postAuthor: jhalek90 » Thu Jul 15, 2010 9:18 pm

My sucba tank was free, and once i removed the stupid fittings on the neck was 1'' NPT.... made going to a normal pipe fitting very easy.
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Unread postAuthor: Technician1002 » Thu Jul 15, 2010 9:52 pm

If you remove the original valve, the dive shop won't refill it.
Some dive shops won't refill a tank without a valid dive card, so only those trained can dive and idiots don't drown themselves trying.

An alternative to a dive tank is a high pressure Nitrogen tank with a regulator. The school that built a QDV competition shirt cannon uses one as most sports arenas won't permit extension cords on the floor for the shirt cannon compressor.

Below is a photo of their set-up. The regulator is set to 100-150 PSI for quick fills, but they only fill to about 35 PSI using a gauge, as that is all that is needed.
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The Arlington team launches some shirts into the upper deck at PGE park in Portland Oregon with Nitrogen. They put one shirt on the roof.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 16, 2010 12:42 am

caspar97 wrote:Luckily for me, money is not a problem and i have a refilling station nearby. My friends are thinking of making a cannon similar to the one here


If you have a HPA tank available, I would go for a metal chamber than can take higher pressures, this will allow you to make a much more compact cannon than the one linked to above, with more power potential.

Have a look here - you can keep the same quantity of air, but by reducing chamber volume and increasing pressure, power goes up very significantly.
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Unread postAuthor: Technician1002 » Fri Jul 16, 2010 12:55 am

The competition rules for the above had a 100 PSI limit. With the restriction, we won the competition. With no restriction, higher pressure and a smaller chamber makes sense. Even with the 100 PSI limit, we would have done fine with a chamber 1/4 that size. We were able to reach our target of the back row of the 300 section on only 35 PSI.

At 100 PSI my small chamber launcher with a 1 inch valve tosses shirts 200 feet.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 16, 2010 12:59 am

Technician1002 wrote:At 100 PSI my small chamber launcher with a 1 inch valve tosses shirts 200 feet.


It would be interesting to see a t-shirt vs ballistic gel test, given your penchanct for damage with soft projectiles :)
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Unread postAuthor: caspar97 » Fri Jul 16, 2010 7:12 am

Do you think that there is a way to keep the normal fittings on the dive tank?
By the way, one of the people I'm building it with is a certified diver
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Unread postAuthor: caspar97 » Fri Jul 16, 2010 7:17 am

See, we are trying to build a launcher that goes far, not necessarily fast.
Technician1002
As far as projectiles go, I can launch a marshmallow at nearly the speed of sound, but I can't launch it the length of an American football field. I can launch a golf ball several football fields distance only using 1/2 the speed of sound.

[/quote]
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Unread postAuthor: Crna Legija » Fri Jul 16, 2010 7:37 am

ive been looking for one of the bigger size fire extingsher to power my soon to come semi. at the maket i allways see 10L stainless steel LPG tanks, do you thnk thay could hold 350psi.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 16, 2010 8:44 am

caspar97 wrote:See, we are trying to build a launcher that goes far, not necessarily fast.


Velocity on its own does not necessarily result in longer range, for example if you load a tissue plug into your barrel it will be travelling much faster than say a steel ball from the same launcher when it leaves the barrel, however it will not travel more than a few feet. It is however an important factor if good range is desired. Since a projectile is "penetrating" the air it is travelling through, the qualities I had mentioned in this post apply to a projectile optimised for long range:

Penetration is a function of many things. If there's one area of research where the search for better penetration is most intense, it's in the field of anti-tank weapons, namely those that function mechanically as opposed to relying on explosives.

Let's take a state of the art projectile as an example, here's a 120mm APFSDS round:

Image

In order to achieve optimal penetration, the following parameters are important:

1) high velocity - if a projectile travels slowly, the target will have time to deform and absorb the blow without penetration, and therefore in order to penetrate well you need as high a velocity as possible. A typical anti-tank round is travelling at around 5,000 fps.

2) high sectional density - in order to maintain its momentum, and transfer the energy in a concentrated manner, you need a projectile that is as heavy and narrow as possible - this is why APFSDS rounds are made of very dense materials such as tungsten or depleted uranium, which being long and thin to give the distinctive arrow shape.
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