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Underwater gun

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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Underwater gun

Unread postAuthor: Sticky_Tape » Mon Apr 21, 2008 4:29 pm

I know that someone already thought of doing this but would this make it easyer to work? it would have water in the air chamber so that water would come out of the gun instead of air that would get rid of all the water to air physics right?
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: pat123 » Mon Apr 21, 2008 4:43 pm

Maybe but not so much water. it would be very hard to pressurize the water, so you would be shooting it only from that little bit of air in the chamber.
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Unread postAuthor: elitesniper » Mon Apr 21, 2008 4:48 pm

water can't be pressurized.
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Unread postAuthor: Sticky_Tape » Mon Apr 21, 2008 4:48 pm

well that's just a conceptual diagram (thanks JSR) and youn could use pressures like 100psi on it.
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Unread postAuthor: joestue » Mon Apr 21, 2008 5:00 pm

All that moving water has to be accelerated, so it's going to suck a lot of the energy out of the system.
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Unread postAuthor: jrrdw » Mon Apr 21, 2008 5:02 pm

I think if you used a purge valve to bleed out all the air and filled the pressurized the storage chamber with nothing but water, it will work. I think you will get better results this way because the air will come out hit water and most if not all forward momentum will stop, making it a weak at best shot. Water on water should flow better improving power.

Thats my theory.
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Unread postAuthor: pat123 » Mon Apr 21, 2008 5:06 pm

water can't be pressurized.

why not?

maybe you could have a pressure washer hooked up to the chamber to pressurize it. they usually pump like 2000psi.
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Unread postAuthor: elitesniper » Mon Apr 21, 2008 5:13 pm

water doesn't get pressurized only the air around it is pressurized.
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Unread postAuthor: joestue » Mon Apr 21, 2008 5:15 pm

The water can be pressurized. because it is under pressure.
Did the volume of water change? no, not significantly.
Therefore both statements are almost true.

Either way, pressurizing a liter of water to 2000 psi might store oh, about .1-1 joules of energy.
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Unread postAuthor: rp181 » Mon Apr 21, 2008 5:25 pm

water can't be pressurized, pressurized air is pushing the water. If you had a container with only water, and hooked a pump to it , the pump would break. that is why it is used in explosives, a container with water has a charge in it, when it ignites, it propells the water out with trmendous force, the force can't be absorbed. Same with shooting a spud gun at a coffee can full of water and a lid. the lid will pop off.
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Unread postAuthor: jrrdw » Mon Apr 21, 2008 5:37 pm

Any hydro-engineers around?
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Unread postAuthor: Fnord » Mon Apr 21, 2008 5:41 pm

Anything can be pressurized, but not everything can be compressed effectively. Water doesn't compress much until extreme forces are involved.

As to the design above, you won't get much power with allthat energy being wasted accelerating the water. A better idea would just be to stick a union on the end of the barrel and hold back the water with some foil.
You could make a homemade camlock system for faster disk changing.
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Unread postAuthor: elitesniper » Mon Apr 21, 2008 5:49 pm

Ohh I guess I was wrong then, I think for a speargun design you should use a really strong spring held in by a sear type thingy, I think it would be more effective then air, for underwater shooting.
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Unread postAuthor: benstern » Mon Apr 21, 2008 5:55 pm

Liquid water is an incompressible fluid. It still means it can be under and exert pressure. (IE at the bottom of the ocean) It just can not be reduced in volume.
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Unread postAuthor: Sticky_Tape » Mon Apr 21, 2008 7:41 pm

Benstern is compleatly right. Did you ever hear of hydro static testing? Where a air chamber is filled with water and then air is pumped in so if the chamber exsplodes there is olny a small amount of energy stored even at say 6000psi. it's like JSR's pengun exsploding compared to a pop bottle exsploding there may be more pressure in the pengun but there will never be as much energy stored in the pengun as in a pop bottle.

1ml at 100psi compared to 2000ml at 100psi 2000ml has more energy.
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