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Dave, I wrote: >>>As for the advantages of a Draeger for deco, which you described below, I >agree, but my one reservation is that, even though it is a good system, it >is still more likely to fail than OC.<< You responded: >>Not in the basic pure 02 mode. No moving parts, manual add valve. How can it be any simpler than that? The 02 monitor is just for grins<< Just be sure & practice procedures for free-flow! The Draeger _is_ wonderfully reliable, but it does have occasional failures (just like OC). Whether the failures are more common than OC, I can't really answer, but they take more skill to resolve. The most common I've seen are demand valve failures - either too high a cracking pressure (as you noted - that's what the bypass is for), or a free flow. Free flow seems to be less common, but takes alot more skill to resolve. Still, since we're talking about deco, when presumably you're not too task loaded, I guess the impact is a little reduced. Seems to boil down to a trade-off, like all of our gear selection choices.... Rich L ----- Original Message ----- From: Dave Sutton <pilots@na*.ne*> To: Rich Lesperance <richl@uf*.ed*>; <techdiver@aquanaut.com> Sent: Saturday, October 23, 1999 9:58 PM Subject: Re: 02 rebreathers for deco > >USN Dive manual quotes about 75% O2 for the standard purge (breathing down > 2 > >bagfuls, exhaling through the nose), so I'd imagine you might get that 90% > >you mentioned if you wanted to do the three of four purges. > > Yup. > > > > >Of course, > >nitrogen is racing out of your system the whole time, so you'd have to > >re-purge a few times during deco. > > > Now, -that- is not something I had even contemplated. -cool-!. > I'll store that gem in the brain cells for future use. Hmmm........ > > > >And the electronics you add (the analyzer) just increased the complexity, > >and decreased the reliability. > > Err.... Not really. A oxy sensor is just a battery. Read the voltage and > convert to percent. When was the last time you stressed out over using > your analizer on the surface? One trick is to measure the output voltage > pre-dive and keep a record of the voltage so you can watch the cell > degrade over time and replace it as needed. This is simple stuff. > But not the stuff that is so mainstream so that everyone is comfy with it. > > > >While I know next to zilch about mixed-gas > >rebreathers, one common complain I hear is that the electronic monitoring > >system, that controls the addition of O2 to the loop, is the catastrophic > >failure point. > > > > Rebreathers are the sort of thing that one approaches like a high > performance airplane. They are not for everyone. But there is > essentially no failure mode that cannot be dealt with by a > -trained- diver with intimate knowlage of the system. In the event > of a total loss of electronics one can convert to semi closed mode > by simply exhaling every 3rd or 4th breath out of your nose, insuring > a constant addition of diluent gas into the loop, thus saving gas use > while insuring a breathable mix. This is a long topic and worth your > research if you are interested. It's funny that most complaints are made > by people that have never used them. To me, the system is totally > understandable and completely intuitive. > > > > > >As for the Russian rebreathers, I've never dove one, but talked to a few > >(spetsnaz) who have - the one guy who was the most garrulous told me it's > >nickname was the widow-maker, or something like that. Whether that was the > >IDA-59 you're talking about or not, I don't know - I'd have to see a > >picture. I'd still be interested in one for shallow stuff, I'd just be > >hesitant to use it with mixed gas. > > > > The IDA-71 has some interesting issues involving automatic > purging of the bag with EAN 40 at about 50 feet and then > automatically repurging upon ascent with 02. But the IDA-59 > is a far different animal. In it's simplest mode it's just a pure > 02 loop, nothing to break at all and stone simple. I'm going to play > with the IDA-71 as a nitrox rig, but I may end up replumbing it > completely. The IDA-59 is staying as-is. There is also an IDA-72 > which I'm scrounging also, which is designed for trimix semi closed > work and may be OK as-is. I'll report when it's in hand. > > > > >As for the advantages of a Draeger for deco, which you described below, I > >agree, but my one reservation is that, even though it is a good system, it > >is still more likely to fail than OC. > > Not in the basic pure 02 mode. No moving parts, manual add valve. > How can it be any simpler than that? The 02 monitor is just for grins. > > > >Of course, since my deco diving is done in > >caves, I'm not too concerned about the size of my O2 bottle. > > > Different arenas require different tools, eh? Understood perfectly. > > > Best, > > Dave Sutton > > > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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