SpudFiles

any body know how much pressure per square inch dry ice makes its long shot but thanks anyways

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At room temperature, it produces a maxium of roughly 800PSI. Search google for "CO2 vapor pressure" to get answears for other temperatures.

800 psi! cra_ ! im gonna put pressure guege on right now

Personaly i think dry ice would be too hard to controle... You would need to have the exact same size peace with the same amount of water each time. Too much of eather and not even a solid steel cannon will hold back the preasure (Kabooom!). any way if you came up with a good system to regulate the preasure you should get some awsome results.

Firemaker:
2" sch 40 steel pipe (common) is rated to about 800 PSI, if I remember right. On the more exotic side, mcmaster carries sch 40 stainless steel in 1.5", rated to 3000 PSI.
Personaly, I'd make the CO₂ generator as a seperate unit, not attached to the launcher. This would be an upright chamber with a 1" or so (steel?) ball valve on the top, most likely a pop-off valve (400 PSI?), and a hose & connector for filling the cannon. The only issue is the connector - it could be annoying to find one suitable for 400+ PSI.

OK solid steel or copper pipe would probably hold up just fine. But as we have affirmed in the past ... sch.40 and other PVC products don't do well under low temperatures and considering dry ice has a surface temperature of -78.5C (That's -109.3F) I would rule it out as a good building material. Also you have to look at the specific cold tolerances of certain glues and salders to insure that the joints don't come apart. Its a good idea, I would just do a lot of research before actually firing this thing.