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Thread: HPA and Co2 mix- someone around here somewhere has done this...

  1. #1
    Administrator AirGunEric's Avatar
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    HPA and Co2 mix- someone around here somewhere has done this...

    I seem to recall someone was experimenting with mixing HPA and Co2 in a rifle tank/reservoir and getting some very good results. Anyone remember who this was?
    I'd say I care- but I'd probably be lying...


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    It was me.

    I was told not to mix but I did to test it out. and my shout count was hight then HPA but the speeds where a bit slower but not enuff to make me stop, but ever since I bought a HPA Pump well
    I don't mix.

    it gave me no problems but was told not too do it.
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    Member Gippeto's Avatar
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    It was Walter IIRC.....

    Found it....

    http://www.network54.com/Forum/79537.../CO2+%2B+air--

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    I remember reading the post recently. It's not the one Gippeto posted, it's recent. I think the guy was from South America.

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    Administrator AirGunEric's Avatar
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    Walter seems to have taken quite a bit of heat on that one. I do like his doubled shot count on the mix vs. plain HPA or plain Co2...
    I'd say I care- but I'd probably be lying...


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    Moderator rsterne's Avatar
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    WOW!.... I chatted with Walter a bit about this on the CAF long ago, but never in depth.... On one hand, we have Steve in NC saying that the two gasses behave completely independantly, the CO2 acts as if the air wasn't in the reservoir.... On the other hand, we have Walter who insists that the total pressure is a combination of the two, and that the blanket of pressurized air keeps the CO2 more in a liquid state, evaporating as the air is used up.... I can't even remember what I said to Walter, but I think it was on the lines of the air effectively makes the reservoir smaller, but with "flexible walls" or some such jibberish.... Basically, I agreed with Walter....

    It is interesting that as the thread develops, Steve suddenly decides the practice is unsafe, as a temperature change would push the pressure of the CO2 up, and could exceed the MSWP of the reservoir.... He didn't give an example, but I will.... Let's say we started with Walter's 700 psi of CO2 at 55*F, and then topped the reservoir up to 2000 psi with air.... Steve is saying that you have 1300 psi of air, plus whatever the CO2 adds, depending on the temperature.... Using that logic, if you now warm the gun to 85*F, the CO2 pressure would be 1050 psi, so the total pressure would have to be 2350 psi.... If you continued to raise the temperature to 100*F, the CO2 would be 1200 psi, and the total would be 2500 psi.... Likewise, if you put the reservoir in a freezer and dropped the temperature to 0*F, where the CO2 pressure should be 300 psi, the total pressure should be 1600 psi.... Why in heaven's name didn't somebody just TRY that?.... It seems to me to be a simple way to determine what is happening....

    PS, my bet is that the pressure will stay at ~2000 psi regardless of temperature.... other than the effect due to absolute temperature slowing/speeding up molecular motion (and hence slightly affecting the pressure) of the mixture.... This can be calculated, and for starting at 2000 psi at 55*F (515 *R), warming to 100*F (560*R) would raise the pressure to 2000*560/515 = 2175 ps, and cooling it to 0*F (460*R) would drop the pressure to 2000*460/515 = 1786 psi.... Steve's theory would predict 2500 psi at 100*F and 1600 psi at 0*F.... It wouldn't take a very expensive gauge to find out who is right, or if the answer lies between....

    Bob
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    Member Hammer Sandwich's Avatar
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    Quote Originally Posted by rsterne View Post
    WOW!.... I chatted with Walter a bit about this .... It wouldn't take a very expensive gauge to find out who is right, or if the answer lies between....

    Bob
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    When exactly was that Frank?


    Quote Originally Posted by FRANK View Post
    It was me.

    I was told not to mix but I did to test it out. and my shout count was hight then HPA but the speeds where a bit slower but not enuff to make me stop, but ever since I bought a HPA Pump well
    I don't mix.

    it gave me no problems but was told not too do it.

  9. #9
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    Interesting thread fellas :)
    Signed up so I could reply here.

    The 'test' was as written up on the Yellow. Results were posted as discovered. Might could do it again with an AT44 or sum such......

    Cheers

  10. #10
    Moderator rsterne's Avatar
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    HI Walter, and welcome.... I know you published the velocities, they are in that thread on the Yellow, linked below.... I think a simple pressure test, using three widely spaced temperatures, would settle what is going on.... Is my summary of Steve's and your positions below accurate?....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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