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Air Tank refilling capacity

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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Air Tank refilling capacity

Unread postAuthor: tweeek » Fri Oct 16, 2009 4:28 pm

Sorry for the noob question. My chamber has a capacity of about 270ci. I was looking at buying a 11 gal 125PSI air tank from HD. How many refils will my gun get with this tank, is it as simple as dividing the capcity of the tank by the capacity of the chamber?

roughly 11 fills @ 125PSI??
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Unread postAuthor: D_Hall » Fri Oct 16, 2009 6:29 pm

What pressure are you trying to take your gun to? If 125 psi, the answer is zero fills. If something less... Well, it depends on what that number is going to be.

But in general....

P1 * V1 + P2 * V2 = P3 * (V1 + V2)

Note that the above does not assume the use of a regulator (but you didn't say if you're using one or not).
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Unread postAuthor: tweeek » Fri Oct 16, 2009 7:42 pm

Can you elaborate on what P & V equals.

Trying to get the gun to 100 PSI. No Regulators, ball valve on the tank, ball valve on the gun.

This is my first spud gun, I built it as a line gun, to get a string from A to B when I setup ziplines, rope jumps etc. I havent got into building the reel yet, I just took it out today to do its first test.

Im wondering why I didn't build a propane metered combustion cannon, because the size of air tank I have to carry with me seems ridiculous. I've read about CO2 on here a little, is that another option for pressurizing, or do I face the same tank size issues?

Any suggestions on reel setup & ammo to be used? 1.5" barrel.
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Unread postAuthor: D_Hall » Fri Oct 16, 2009 11:23 pm

P = pressure.
V = volume.

So...

V1 = 11 gal = 2541 ci
V2 = 270 ci

P1 = 125+15 = 140 psia (note that I'm rounding 1 atm to 15 psi)
P2 = 15 psia

So...

P3 = (140*2541 + 15*270) / (2541+270) = 128 psia = 113 psig.

So your first shot will be at 113 psi.

For your second shot....

P1 = 128 psia
P2 = 15 psia

P3 = (128*2541 + 15*270) / (2541+270) = 117 psia = 102 psig.

Looks like you're going to get 2 shots out of that tank before the pressure falls below 100 psi (3rd shot is going to be on the order of 90 psi though, so not tooooo bad).


Seriously though, for what you're trying to do you're going about this all wrong. Ball valves? Pre-filled tanks? You need to do your homework. May I suggest you start HERE.
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Unread postAuthor: tweeek » Sat Oct 17, 2009 2:26 am

D_Hall wrote:Seriously though, for what you're trying to do you're going about this all wrong. Ball valves? Pre-filled tanks? You need to do your homework. May I suggest you start HERE.


Thanks for clarifying the math.

But I have to ask, what is wrong with using ball valves for filling the chamber. I have one on the tank and one on the chamber... The ball valves are only for filling the chambers, not for launching the projectile. I use a modded 1" sprinkler valve for launching. What homework am I missing?

Thanks, the PDF is veryinformative, gives examples of tennis ball launchers, but goes into no specific detail about what system may work best for me. I need to be able to send a line 600ft.
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Unread postAuthor: D_Hall » Sat Oct 17, 2009 2:52 pm

OK, my appologies. WHen you mentioned ball valves I thought you meant you were using them to fire with. As for filling your chamber, it doesn't matter what kind of valve you use (thus, I wouldn't even expect it to be mentioned).

As for the tennis ball launchers, no, they may not meet your precise needs, but they outline the methodology you need to adopt.
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