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> From ec96 Fri Aug 5 20:27:21 1994 > Subject: Re: mixture rebreathers (automatic and otherwise) > To: A.APPLEYARD@fs*.me*.um*.ac*.uk* (A.APPLEYARD) > Date: Fri, 5 Aug 1994 20:27:21 +0100 (BST) > In-Reply-To: <1DF149134F75@fs*.mt*.um*.ac*.uk*> from "A.APPLEYARD" at Aug 5, 94 04:54:20 pm > X-Mailer: ELM [version 2.4 PL23] > MIME-Version: 1.0 > Content-Type: text/plain; charset=US-ASCII > Content-Transfer-Encoding: 7bit > Content-Length: 6962 > > Hi, > > I'm new to the techdiver list and so am usure of what info has been > passed about before. However I did go on a one day intro course run by > Peter Ready to discuss and try rebreathers. An informative morning was spent > discussing pros and cons of all the reabreathers on or about to come on to the > market (including military spec rebraethers like the Rexnord and the Draeger > units. We then all had a dive using two of Peter's Prism rebreathers on Nitrox. > > > (1) Has there been any new news in the last few weeks about AMRB's (= > > automatic mixture rebreathers) and other mixture rebreathers? (i.e. price; > > makers; when likely in the shops; etc) > > At the Slide show/lecture some pictures of the Oceanic/Carmellan > Research rebreather were shown. This is fully automatic and was said to be > available (at a cost !!) "in a few months". The military Draeger unit was not > intended to be for sale to civilians. Very little was said about Bill Stone's > USA rebreather, although a nitrox sport version was said to be shown at a > diving trade show in the USA last Xmas and available in '94. This unit is > supposed to be available in oxygen + diluent fully closed circuit mode also. > > > (2) It is said to be possible to run the Prism with different gases in its > > two cylinders. If these two gases are oxygen and diluent, and as the Prism is > > said to be modular so that different parts can be put together for different > > purposes, when and if a reasonably cheap and <reliable> automatic controller > > for AMRB's is designed, would it be possible to design such a controller that > > could be added to a Prism to make it into an AMRB without having to hack the > > Prism's basic construction about? > > I specifically asked the same question about converting the Prism from > 'semi-closed'/mixture-in-the-cylinder mode to a fully-closed mode..using one > cylinder for oxygen and the other for diluent. Peter's answer was that this > could be done now with no difficulty. He will basically tailor the Prism to > your requirements (and pocket !!) > > He did make several pertinent points though : > > #1 He, like all the rebreather manufacturers, is worried about someone > getting hurt/bent/killed on a rebreather, especially when they are new to the > diving public. Bad press early-on could put an effective stop to all rebreathers, > even if the accident was unrelated to the use of a rebreather. The Health and > Safety Executive are keeping a very close eye on the whole scene. This is one > of his reasons for running the intro courses (apart from exposing a potential > market to his wares). The more safe diving hours he can demonstrate and > document on the Prism, the stronger case he can make to the HSE to be allowed > to continue selling Prisms when the inevitable accident occurs (whether on a > Prism or not). This makes good sense. > > #2 In view of this, he wants the diving marketplace to take small steps > into using rebreathers. He will sell a semi-closed nitrox unit first. After > a prescribed number of diving hours on this, he will allow it to be used on > other mixtures, but still in semi-closed mode. Following success at this, > he will finally allow the rebreather to be converted into fully automatic/fully- > closed circuit mode. There was no suggestion that this conversion would 'hack > the basic construction about'. > > #3 'Bail-out' and scrubber limitations were two considerations that > had not really occurred to me before the intro course. Although the full-closed > unit will potentially have a much longer u/w duration than the semi-closed unit, > the duration of the scrubber for either unit (6 hours) is more likely to be the > controlling factor. The semi-closed unit carries it's own bail-out if something > goes wrong..by breathing the mixture in open circuit mode. Use of a fully- > closed unit neccesitates strapping a large extra cylinder + reg to your waist > for bail-out. This detracts from the advantage of lightness of a rebreather > when compared to conventional multi-cylinder/mixed gas long duration diving. > > In the light of this the semi-closed unit starts to look more attractive > than at first. The fully-closed unit scores if you want to go so deep that a > suitable mixture in the cylinders at depth is unbreathable at the surface. > Alternatively, if you just want to jump in and see what happens..this is > possible if the ppO2 is held constant by the fully-closed unit for any depth. > For the semi-closed unit, the max diving depth must be planned before the > cylinders are filled. > > > (3) Of the various makers of AMRB's and other mixture rebreathers, do any of > > them (as far as is known) read Techdiver? > > Don't know. > > Further comments as follows : > > 4 divers from Liverpool University went on the intro course. We > are the ones normally doing the deeper diving on air (50m-60m+) using redundant > sets, etc. Although the Prism intro was interesting, no-one rushed out to buy > one. You didn't seem to get much for 2 thousand pounds. You provide your own > 2*7 litre cylinders, 'wings', bail-out regulator etc. You get a counter-lung bag > + fittings, a scrubber unit, twin hose pipes + a mouthpiece and a 'constant mass > gas valve'. We guessed that all this would retail at a max of 750-1000 pounds > and that the rest of the cash was going into repaying development costs. With > the alternative units selling at 5000-20000 pounds, we are waiting to see what > happens to the market over the next year or so. > > The Prism unit seemed very functional, but a little 'Heath-Robinsonish'. > Some of the fittings looked rather vulnerable and may have been protected better > with a little more thought. We said so at the time. Peter's reply was that > the two units we were using had had a lot of use and abuse and were showing no > signs of distress. I suppose that is a fair comment, but I would have preferred > the Prism to LOOK a little more rugged. > > Putting the counter-lung on the front, rather than putting everything > 'in a box' on your back struck us all as a sound concept. > > That's about all I've got time for. I hope this is of some use/interest. > Sorry a lot of the info on other rebreathers is 2nd hand. Maybe someone else > will do better. > > > Regards, Steve M. > > ******************************************************************************** ********** > * * * > * Dr. S. G. Millard * E-Mail : ec96@li*.ac*.uk* * > * * * > * Department of Civil Engineering, * Tel : 051 794 5224 (UK) * > * University of Liverpool, * 44 51 794 5224 (International) * > * PO Box 147, * * > * Liverpool L69 3BX, * Fax : 051 794 5218 (UK) * > * UK. * 44 51 795 5218 (International) * > * * * > ******************************************************************************** ********** > > > > -- > > Send mail for the `techdiver' mailing list to `techdiver@opal.com'. > > Send subscription/archive requests to `techdiver-request@opal.com'. > > > >
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