I think someone should put a gauge on things and give it a try. Of course, that would be me trying to figure out how to get 55% Co2 in a bottle which I'm bound to ne 'approximating' more than anything. Will see if I can find some time soon for this...
I'd say I care- but I'd probably be lying...
AT44 has a gauge so could repeat this test at some point.
Fill the AT44 reservoir on its side using the bleeder to vent excess liquid would get you about 45% by volume. Good enough for the test.
Walter.....
Here are my real results in a 2260 PCP with a mix of CO2 and Air May 28 2008, 2:35 PM
I have my 2260 setup for the Discovery games and so limit it to the 2,000psi that the Disco gets.
Made a drop tube for CO2 filling and set it up for 55% by volume in my 19.5 x 0.745" reservoir.
Filled with CO2 to that volume and then topped it up with Air to the 2,000psi limit.
So went outside in the shade to shoot..... first ten would not read on my Chrony......
So setup in the bright sun and got these numbers: using Crosman 14.3gr HP
32 shots ave 611fps
next 32 shots ave 612
next 32 shots ave 627
next 32 shots 634
next 32 shots 653
next 32 shots 674
next 32 shots 684
shot 10 more until the fps fell to 595 and the ave was 624fps
Discounting the first 10 this little dual-fueler got 234 shots from a 'fill'
Will test some more after lunch to determine CO2 only and Air only results.
Walter....
edit: 3,062.7fpe from that 140cc reservoir...................
Interesting
As far as I know.
-The amount of CO2 that will be in the Air /CO2 mixture will be temperature dependent. As the temperature rises there will be a higher percentage of CO2 in the mix.
-The CO2 will gas off to maintain the molecular density at a given temperature.
- Once in the mixture the gases will not separate until the temperature is dropped to the point where the CO2 will revert to liquid. Thus any pressure/temperature equations must treat the mixture as a distinct gas not two independent and exclusive gases
Walter is correct.
Sean
Why not take a freshly filled CO2 tank (say a 9 oz, with an actual 9 oz. of CO2 in it) and rig up a fitting to add air to it.... The tanks are rated at 1800 psi and have a 3K burst disc.... Let it stabilize at room temperature (~20*C) to ~850 psi, and then add HPA until it is at, say 1700 (ie adding ~850 psi of air) so the pressure is half and half.... Put a gauge on the outlet and let it stabilize again and record the temperature and pressure.... Then throw it in a freezer, let it stabilize and then record the temperature and pressure again.... If the temperature drop is about 30*C, the pressure should drop about 10% to ~1530 psi if Walter is right.... If Steve is right, it should drop to about 1200 psi, depending on the exact temperatures.... To confirm, find a location that is about 40*C, and let stabilize and record the temperature and pressure again.... Should be pretty straightforward what is happening....
Bob
Last edited by rsterne; Sep 07 2012 at 01:39 PM.
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Go for it Bob.Originally Posted by rsterne
Your experiment is going to be a little tricky Bob
I think what it is going to show is how many moles of each gas exist in the gaseous state. Using Daltons Law of partial pressures.....( This is where the confusion exists I believe) Daltons Law of partial pressures states that the total pressure will be the sum of the pressures exerted by each gas
Reading that it would seem that steve is correct,
however it is a misinterpretation because the calculation is based on moles of gas and at these pressures both the air and the co2 are actually supercritcial fluids.
Sean
I don't have a CO2 tank, and I'm not interested enough to spend the time and money to drive 4 hours to purchase one and get it filled, just to do the experiment.... I was just suggesting something that could possibly settle the debate....
If I read Steve's argument correctly, the air in the tank isn't affecting the CO2 in any way, it is only affected by the temperature.... Therefore the CO2 follows the accepted chart (below) completely.... That would mean that at 70*F (for a tank between full and 1/3rd full), the CO2 was in the green (liquid/vapour) area of the chart, not the yellow (supercritical) region.... It would also mean that for a tank filled to 100%, if you increased the temperature to 120*F, the pressure of the CO2 would increase to 1900 psi, and then you ADD the air pressure onto that to get your total.... That was his safety concern.... If you started at 70*F (where the CO2 was only 850 psi), then added air to bring the pressure to 2000 total (ie 1150 psi of air).... then warmed the tank to 120*F, the total pressure would be 1900+1150 = 3050 psi....at these pressures both the air and the co2 are actually supercritcial fluids
Personally, I don't see how either can be the case.... I would argue that if you follow the 70*F line to the right, and then upwards to where the actual total pressure inside the container is, that is what the state of the CO2 is.... eg. at 70*F and 1500 psi it is in the middle of the blue (all liquid) area.... My argument was (and as I think about it, still is) that the air reduces the space available for the CO2, just as if it was in a smaller (flexible) container.... In other words, the HPA makes the CO2 think it's in a smaller container than it really is (because of the higher pressure) and it condenses to all liquid.... Find where the temperature line crosses the total pressure, and you will know what the CO2 is (liquid, vapour/superfluid, or both).... I'm pretty sure Walter agrees with me, but I'm not going to put words in his mouth.... My theory is that, starting with the above example, the air would be used up first, the pressure dropping, and the CO2 state (liquid) "sliding" down along the temperature line until it reaches the border between the liquid (blue) and liquid/vapour (green) phase interface.... At that point (in this example 853 psi), the CO2 would begin to boil, and then you would start using both air and CO2 at constant pressure (the air in ever decreasing percentage, as the CO2 vapour is being replaced as the liquid boils) until both are exhausted, or you refill the tank.... That theory, and $1.50, will buy you a coffee if you don't go to Starbucks....
Someday, somebody will care enough to find out....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Shots on just air May 28 2008, 4:57 PM
filled to 2000psi
10 went 510-578
10 went 568-596
10 went 597-623
10 went 623-648
10 went 648-682
10 went 681-717
10 went 717-756
10 went 756-789
10 went 789, peaked 791 down to 712
next 7 went from 711 down to 594
stop
Made no changes to gun setup for the test on air.
So blead off the little reamining air and filled with CO2
muzzle down for a minute and then one shot at 654fps
letting gun stabilize in shade.
Walter....
Shots on CO2 May 28 2008, 5:31 PM
30 ave 680
30 ave 680
30 ave 678
10 ave 672
10 from 672 down to 622 ave 646
next five 622,619,615,612,609
stop.
weighed gun full = 5.08 pounds
weighed after shots = 4.96 pounds
CO2 consumed = 0.12 pounds = 1.92 ounces
Walter....
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