AlexL
Contributor
that's not what i said at all. at least that's not how i intended for it to be taken.
i'm going to concede this discussion, as my statements were for a case (average mix over time) that is not applicable to diving, the dynamic loads of breathing cycles, nor to the OP's original subject. my '50/50' statement was only for a timed average, ie: you take a post and transfill to an empty 3rd tank. i think @tbone1004 's statement of a static '30/70' or '60/40' are a bit off the mark, but they were qualified as slightly hyperbolic. i do agree that density, viscosity, temperature, compressibility and other factors that make gasses non ideal play a large role, especially at higher working pressures. instantaneous mix at the post is going to vary between the tank mixes; in broad strokes with the start of the draw favoring the tank the post is located on due to the lower flow restriction vs the manifold, and the recovery time favoring the other tank as the pressure drop in the tank the post is on increases the pressure differential across the manifold and drives a flow from the other tank back into the first post/tank. next time im able to get a nitrox fills on demand, plan to burn a few cubic foot to partial fill a mismatched air/32 twin set and see what the analyzer spits out on each post just to satisfy my curiosity, then completely drain the air side, and complete the fill on 32.
furthermore, i am in complete agreement with the posters that have stated that the only way to 'fix' a pair of mismatched tanks is to ether drain and start again, or treat them as independent tanks and partial pressure each individually.
finally, i am also in complete agreement with @tbone1004 that diving a set of mismatched manifolded tanks is fundamentally a bad idea, and can easily maim/kill you if you're diving mixes outside the acceptable range of the plan in either tank.
