12gram Pressure Chart

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Postby akb » Tue Apr 05, 2005 10:42 pm

Test with 3x6 chamber and 12 gram cylinder in bicycle tire fill adapter:

Initial pressure rose to 80 psi.
Waited approx 30 seconds, rose to 85 psi.
Started blowing gently (warm air) across the cylinder.
Waited another minute, got to 91 psi.
Waited another few minutes (now no ice on the cylinder, so no dry ice inside, pressure rose to enough to trigger the overpressure valve at 100 psi, estimate it would have made approx 103 psi.

-- akb
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Postby Ian2accurate » Fri Aug 26, 2005 9:50 am

Just for the books I'm going to put in the formula for fill ratios.
This is how you can figure out how many shots or fills you would have from larger volume and pressure to slightly smaller volume and less pressure. Its going to be regulated down to a certain pressure that will remain constant.

To figure this out, you would use piv-nert...PV=nRT... and calculate how much moles of the gas you would need to fill a chamber with a certain pressure @ some temperature. Then, you can calculate the number of moles in the high pressure gas chamber by using the PV=nRT, or using the mass I guess...

Then just divide the larger amount of moles (high pressuren tank) by the smaller amount of moles (lower pressure tank).

Ex:
Chamber- 45Ci chamber filled to 120psi.
Filling Tank-2.5lb CO2 tank.
We'll say 70*F
<hr>
Moles in filled Chamber:
120psi ~827.37kPa
45ci ~0.74liters
21.1*C ~ 294.1K

PV = <i>n</i>RT
(Pressure(kPa))(Volume(L))= (number of moles(n))(Universal Gas constant(kPa*L/n*K))(Temperature (K))
(Im just going to cancel out the unnecessary units for simplification)
827.37*.74=(<i>n</i>)(8.31(mol^-1))(294.1)
(612.25/(8.31)(294.1))mol=<i>n</i>
<u>.25mol=<i>n</i></u>
<hr>
Moles in 2.5CO2 tank:
Amount of grams/Molar Mass CO2
1133.98g/44.01 (just for simpiflication I'm just gonna say that the 2.5lbs is the exact weight of just the Co2 gas)

Moles in 2.5lbs. CO2 tank:
Amount of grams/Molar Mass CO2
<u><i>n of Co2</i> ~ 25.77mol</u>
<hr>
25.77mol/.25mol = <i># of fills</i>
<u><i># of fills</i>= 103.08</u>
<hr>
So...that one tank would last a pretty long time (at 70*F and 120psi anyway). And from there, just substitute in different numbers for the ones I have above if you want to figure something out yourself.
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Postby akb » Sun Dec 04, 2005 8:59 pm

Note that using ideal gas laws is what I was doing above, and experimental results do not agree with that assumption. I suspect that the CO<sub>2</sub> gas is very cold and so room temperature is the wrong value. Do some measurements and see what you get. The 12 gram is an easy one to use for measurement since you know the amount of gas you have. Open it into a known volume and see what you get, and compare that with what you expect.

-- akb
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Postby Vetack » Wed May 31, 2006 1:45 am

When I first started using 12 grams, I was having trouble finding info on the volumes and pressures. I found some good info on a website and used their formulas to create an excel spreadsheet. Don't know if anyone could use it, but it has 12 gram pressures as well as volumes of SCH40 and generic pipe sizes as well:

http://www.vetackonline.com/at4/co2pvc.xls
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