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From: ddrake01 > I have two different friends here on the net who are thinking and planning > on building rebreathers, hopefully for eventual resale to the rest of us. > Each has asked me several general questions and asked that I post the > questions here. They'll each get to see the responses that way. Harold and friends, My preference would be redundancy, redundancy, redun...for safety. Then my goal of using a rebreather would be to maximize bottom time and minimize deco. I'd have a primary automatic O2 adjusting rebreather in a closed circuit. A manual system would be employed automatically if errors occured in the automatic part. This would be accomplished by separate monitoring circuits/sensors. In a fail- ure the system would be semi-closed. Separate, backup bottle(s) of gas would be used to make up the extra volume of gas lost due to the semi-closed system. This backup system would be manually or automatically adjustable, depending on the failure. Of course the diver has their choice in this at all times too. Alarms should be activated when safety parameters are exceeded. Ideally, the unit would keep track of scrubber capacity and inform the diver when 1/3 of any restricting supply/function has been met. Price attractiveness will always be subject to budget, just make it as low as possible. Being an engineer with some Biomedical Engineering training/experience, I am very interested in knowing more about the construction and functioning of the rebreathers. Even though I would be leery of using a model that has not been thoroughly tested (i.e. one made in a garage), I would be greatly appreciative of knowledge that will help me evaluate construction, design choices and quality in general. I feel others will want to know this information too. Therefore, please post the information you three collect to either the list, or send it to me directly. Some suggestions on design: have three sensors for monitoring problems. If one reads in a warning range indicate a fault. If two show a problem say for CO2, an exhaust should be opened to make the system a semi-closed to prevent buildup of CO2. Use a relay or something like that which will activate a servo that opens an exhaust valve. If automatic control of PPO2 can't be controlled, then I'd be concerned about accidental O2 toxicity. I feel that a system like a rebreather should be able to at least make you VERY aware of the O2 problem and/or remove the toxicity problem associated with going down with a setting that doesn't change till you activate it. Task loading can be a big problem. If a rupture in the drysuit, BCD or any other unforeseen event such as heavy downward current takes the diver deeper than planned very quickly, the situation could become very bad. What do you do first, inflate backup floatation or decrease PPO2? Can you do both while being scrubbed against a wall of reef/steel/rock/mud/kelp. I realize that traditional diving with Nitrox can get you into that situation, but the rebreather that I use should take full advantage of the ability to change mixes to make the dive safer if possible. For example, a computer not only keeps track of time and depth, it logs automatically so you don't have to reset analog gauges and timers, or figure out a new deco stop, air remaining, etc. on a difficult dive or ascent. In the choice between an electronic dive timer or computer, I'd take the computer unless I have specific needs. If I am diving in an area that has a max bottom, which in wreck diving is usually the planned bottom, the manual system would be satisfactory. What might could be a solution is to build into a manual system the ability to convert to an automatic system once it has completed design and testing. This is often done now when programming new programs. Modularity and easy modifications are aims of the initial design and structure of the program code. Well, that's about it. I don't know everything about rebreathers, so if I made gross errors, please forgive me and maybe quietly send me a message. I did not want to cover all bases with this message and may need to clarify some statements. If there is question or ridicule, please check with me before using group bandwidth to cook me. The water's warming up here, can't wait... DAVID DRAKE AHDNN1A.DDRAKE01@ED*.CO* ROMULUS, MICHIGAN EDS/GM POWERTRAIN 8-375-5467 (GM NET)
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