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Roberto Bagnasco <divetek@we*.ch*> writes: > >I use a standard Sherwood piston 1st stage with a yoke. To this I run a > >100' Hookah hose to a "T" > > If your first stage is good enough, you will be able to support two divers > on the same hose, but: > The flow of gas is a function of the intermediate pressure and the diameter > of the hose. Let say you put the second stage at 10msw/30feet, you are > dealing with 1bar more pressure then the surface, where you first stage > still delivers the ambient pressure plus let's say 10bars, your actual > intermediate pressure at the second stage is one bar less then it should > be. > Isn't it a good idea to tune your first stage intermediate presure one bar more? > But again if you use the same regs and you ascend to a shallower stop, > 3msw/9feet, then you will have a higher intermediate pressure. > Usually I do nothing and it still work, but I would like some comments on that. One bar more interstage pressure is only 14.7 psi, or about 10% more than normal, so it's not a terribly big difference. Divers will be resting, and at a relatively shallow depth, so gas demands will be far less than they would be for a single diver at serious depth. A 100' hose contains a lot of gas, and will act to buffer the divers' demands. Part of an inhalation will be satisfied by gas already in the hose, and the first stage will still run for a second or two after the diver stops inhaling. I've been on a boat while two famous technical divers were breathing from a setup like the one described; I could hear the first stage working, but it didn't sound like it was being punished too hard. However, it was louder than my own deco reg, which never gets used more than about 1' from my face. Carrying your own deco gas has the advantage that you can deco on a free ascent if necessary; the aforementioned divers found their way up the line and across to their deco gas that day in 18 inch viz. However, probably better than speculating about breathing performance from this setup would be to try it out; I'd try setting the thing up with air (not O2) and taking the hose down gradually as far as it goes and seeing if two divers can outbreathe it. -- Anthony DeBoer <adb@on*.ca*> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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