OK, the movie is kind of boring so I messed with the fill calculator. I assumed 66ft3 as the "big tank" and 33 ft3 as the "smaller tanks". I used a fill pressure of the tanks of 4250psi, a fill pressure for the gun of 3600 psi and refilling them at 2200 psi. I assumed the gun stores 220cc of air. These are roughly right for one of my P35s (so I could sanity check the result).
With those assumptions I would get 13 full fills from the big tank and 6 from each of the smaller ones.
Then I started different assumptions for doing a partial fill from one smaller tank and then raising it to 3600 with the other smaller tank. The best strategy I came up with is filling from 2200psi to 3100 with one tank then from 3100 to 3600 with the other. That would give 18 full fills. So you gain 5 fills, in theory.
The worst strategy I calculated was filling from 2200 to 2900 and then 2900 to 3600. The tank in the second fill would only give you 13 fills - so no gain. Planning the strategy is important.
This all ignores the loss of the air in the lines of the fill set from each fill operation. That would double with the partial fill case so you'd probably loose a fill or two. But still you would get something for your trouble. If you rig up lines that minimize the losses or use a "EZ fill" on each line you might get close to these numbers.
The other way this is a bit theoretical is the calculator only tells you full fills. I usually keep using the tank down to something like 3200 or 3300 psi. That also gives you a bunch more fills. But it works for big or small tanks. Using partial fills minimizes the benefit of multi stage filling. The gain from that strategy is in using the tank more fully. But if you use partial fills you are doing that already. In the "best" two tank scenario you quit when one tank gets below 3600. I pretty much always go below that. But the other tank in that scenario keeps getting used until you go below 3100 psi. Sometimes I go that low but not always.
So unless you only use full fills, fills to the limiting fill pressure, I still don't think it matters much if at all whether you get 1 bigger or two smaller bottles. You can get more full fills from two smaller ones if you are willing to fill your gun twice each time but if you use partial fills that benefit would seem to pretty much go away.
With those assumptions I would get 13 full fills from the big tank and 6 from each of the smaller ones.
Then I started different assumptions for doing a partial fill from one smaller tank and then raising it to 3600 with the other smaller tank. The best strategy I came up with is filling from 2200psi to 3100 with one tank then from 3100 to 3600 with the other. That would give 18 full fills. So you gain 5 fills, in theory.
The worst strategy I calculated was filling from 2200 to 2900 and then 2900 to 3600. The tank in the second fill would only give you 13 fills - so no gain. Planning the strategy is important.
This all ignores the loss of the air in the lines of the fill set from each fill operation. That would double with the partial fill case so you'd probably loose a fill or two. But still you would get something for your trouble. If you rig up lines that minimize the losses or use a "EZ fill" on each line you might get close to these numbers.
The other way this is a bit theoretical is the calculator only tells you full fills. I usually keep using the tank down to something like 3200 or 3300 psi. That also gives you a bunch more fills. But it works for big or small tanks. Using partial fills minimizes the benefit of multi stage filling. The gain from that strategy is in using the tank more fully. But if you use partial fills you are doing that already. In the "best" two tank scenario you quit when one tank gets below 3600. I pretty much always go below that. But the other tank in that scenario keeps getting used until you go below 3100 psi. Sometimes I go that low but not always.
So unless you only use full fills, fills to the limiting fill pressure, I still don't think it matters much if at all whether you get 1 bigger or two smaller bottles. You can get more full fills from two smaller ones if you are willing to fill your gun twice each time but if you use partial fills that benefit would seem to pretty much go away.
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