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"How Much CO2 do I need?"

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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"How Much CO2 do I need?"

Unread postAuthor: BC Pneumatics » Sun Apr 01, 2007 9:52 pm

For all those people out there looking for a rough idea of how much CO2 they will need for a chamber of any given size-
Just multiply the volume of your chamber (In Cubic Inches) by the constant 0.008475 This will give you the ounces of CO2 needed at 120psi, 73*f, needed for each chamber fill.

Example:
3.14 x (1/2) x 3"id x 36"length chamber= 254.34ci x 0.008475 = 2.155oz of CO2.


Edit by MrC:

Thanks to Davidvaini and Ragnarok for this calculation table:


http://www.spudfiles.com/forums/viewtop ... tml#229345

Image

Alternative Word or PDF file available below.
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Unread postAuthor: A-98 » Sun Apr 01, 2007 10:44 pm

how would you calulate it for different pressures, say 250, or 100.

thanks alot though, and i could definitely use this.
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Unread postAuthor: BC Pneumatics » Mon Apr 02, 2007 12:18 am

Ideal Gas Law
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Unread postAuthor: demilus » Mon Apr 09, 2007 9:42 am

And I thought that I'd never use the stuff I learned in Chemistry class :D

EDIT: I just realized, that the calculations need fixing.
It's pi*(radius of inner diameter)^2 * length of chamber = volume of chamber

NOT diameter of chamber * length of chamber

I think you knew this but you just forgot to write the equation. (254 is the volume of your example chamber, but 3*36, which equals 108, is not)

I'll delete this when it gets fixed :D

Fixed it, thanks :oops:
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Unread postAuthor: randompkguy » Sat Aug 11, 2007 5:48 pm

what if your regulator is graded in psi? is there a coefficient of expansion that you can multiply the psi by to get your final psi? (at 80 degrees)
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Unread postAuthor: ALIHISGREAT » Sun Nov 04, 2007 8:05 am

what about if i wanted to fill to 100psi?
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Unread postAuthor: BC Pneumatics » Sun Nov 04, 2007 10:14 am

You would need .83x as much.
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Unread postAuthor: ALIHISGREAT » Mon Nov 05, 2007 2:28 pm

thanks, i found a 12g co2 adapter in the garge yesterday, it could be interesting to see what kind of pressures i can get in my 6mm sniper :twisted: also what if i want to work it out for different temperatures?
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Unread postAuthor: Ragnarok » Mon Nov 05, 2007 3:03 pm

The ideal gas law again, I'm afraid.

A slightly different equation is this one:
Ounces of CO2 = Chamber volume in Cubic inches * Pressure in psi / (Temperature in Fahrenheit + 460) / 26.5

That includes temperature and pressure and gives practically the same answer.
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Unread postAuthor: ALIHISGREAT » Mon Nov 05, 2007 3:19 pm

ahh thanks i will go and get my pencil! ok so at 10 degrees c i need 41.5oz to fill my 6mm to 250psi... which is quite alot :(
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Unread postAuthor: Ragnarok » Mon Nov 05, 2007 5:41 pm

ALIHISGREAT wrote:ahh thanks i will go and get my pencil! ok so at 10 degrees c i need 41.5oz to fill my 6mm to 250psi... which is quite alot :(

Wow, you have a 36.76 litre chamber.

Astounding for a 6mm sniper. I think you may have put the wrong numbers in, or mixed up the ordering of the functions. Are you sure you didn't go:
((Volume*Pressure/Fahrenheit)+460)/26.5
Rather than:
(Volume*Pressure/(Fahrenheit+460))/26.5
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Unread postAuthor: )DEMON( » Fri May 16, 2008 12:15 pm

So what if I had a chamber of 40 cubic inches and 12grams of liquid co2?
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Unread postAuthor: BC Pneumatics » Fri May 16, 2008 12:25 pm

148psi @ 73*F, though I have to point out that the CO2 will no longer be in liquid form at this point.

Luckily gases are very easy to work with. Half the volume (20 CU) will give you twice the pressure (300psi), and increasing the chamber to 50CU, the pressure drops to 118psi.

For further manipulation...
P1V1=P2V2, where P= pressure and V= volume.
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Unread postAuthor: )DEMON( » Fri May 16, 2008 1:05 pm

Thanks for the help :)
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Unread postAuthor: BC Pneumatics » Fri May 16, 2008 2:52 pm

Well, most of the credit goes to Clapeyron, but I'm glad I could help.
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