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On Thu, 30 Apr 1998, Arclight wrote: > Rebreathers basically do 3 things: > > 1. Scrub off CO2 > 2. Inject O2 to replace what is used > 3. Inject a dilutant gas if needed to replace volume > > Am I correct? Yup, that's pretty much it. > I know that dilutant and O2 are sometimes combined in > semi-closed circuit units. What range of "breathing gas" are modern > rebreathers capable of delivering with adjustments? semi-closed units deliver whatever gas is in the cylinder. Fully Closed Circuit units (CCR's) can mix any gas you want on the fly, by varying the amount of o2 in the mix. > Is it possible to go > from a bottom mix to a deco gas while using only rebreather controls? If > so, is it done? Absolutely. Do it all the time. Alot of CCR guys have two dilent bottles, one with trimix or heliox and another with air. You turn a valve to switch between the two. You use the air as diluent for decompression, mixing whatever PO2 Nitrox you want, up to 100% O2. That is one of the great powers of a CCR - because you can so easily control the fraction of O2, you get a near-perfect decompression profile - it's like optimizing your ascent with 20 or more successively richer nitrox mixes. Plus of course, CCR's are the ultimate for gas consumption. A 13 cu. ft bottle of helium with last for many hours at any depth - your gas consumption does not vary with depth. Semi-closed units like the Draeger are really just gas optimizers over open-circuit. Because you can't vary the O2 fraction in the mix, you get no deco advantage. -Will -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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