Thanks for that (see below). I realized that I should have worked it out that way but would have had to think about it a bit more and spend some time looking up the numbers. On that basis an 8g cartridge of CO2 will not get the tire to the desired pressure, but should be much better than I experienced. I have ordered some new cartridges and will see how the inflator performs then. Assuming some leakage during the filling process, the tire should be rideable with one cartridge and fully inflated with 2.
Hugh Thornton
Cheshire, England
From: M-gineering <info@m-gineering.nl> Subject: Re: [CR] Pennine CO2 Tire Inflators To: Cc: "Classic Rendezvous" <classicrendezvous@bikelist.org> Date: Monday, 27 April, 2009, 10:34 PM
Hugh Thornton wrote:
> Finding the cartridges still available, I checked the specification and saw that they contain 8gm (10cc) of CO2 at 900psi (but it doesn't say what temperature gives that pressure, so I assume about 18degC). I then calculated that the volume of a tire is about 800 times the volume of the cartridge. Looking at a phase diagram of CO2, it will not liquify at 900psi at 18degC so it seems reasonable (to me anyway) to assume that Boyle's Law applies and that Pressure x Volume is constant (once everything is back to the same temperature). On this basis, 10cc at 900psi expanding 800 times gives a pressure not much better than 10psi. Which seems to confirm my impression that these inflators aren't much good unless you have a pocketful of cartridges and almost as much time to spare as it would take to inflate the tire with a pump.
a tyre has a volume of 0.8 liter, which is 7 x 0.8L of gas at normal pressure = 5.6l
5.6/22.4= 0.25 mole of gas= 0.25 x 44 = 11 grams co2
mvg
Marten Gerritsen
Kiel Windeweer
Netherlands