It seems a very long time since the Draeger semi-closed circuit rebreather (SCR) was introduced to the leisure-diving market. Its infancy has not been without problems, including an aftersales service that was often open to criticism. Enthusiastic manufacturers have unveiled endless rebreather concepts at dive shows during the past few years. Some even offered training programmes for their units, but among all the hype, the Draeger Atlantis 1 was unique. You could actually buy one! Being first in the market with any product can give the manufacturer a clear advantage but the penalties can also be punitive. With the Atlantis 1, DrÃ?ger took the route of simplicity. Its rebreather is a semi-closed-circuit design with fixed flow rates and an over-riding demand valve which will cut in if there is insufficient volume of breathing gas in the counter-lung. Draeger did not want any of its new-wave divers getting hurt through making the wrong decisions - so it made the decisions for them long before they entered the water. The first year is a dangerous time for any new product, and Draeger's was no exception. In use the Atlantis 1 was revealed to have defects. None was severe, but there were so many of them. There remains a swathe of disenchanted owners out there, especially those who bought their units at the launch price, a whopping $5000! The people at Draeger at last identified all the problems, and there were so many changes that they had what was almost a new product. So they gave it a new name. Exit the Atlantis 1, enter the Draeger Dolphin. It was launched a while ago, but now you can actually get hold of one in the UK! DrÃ?ger has got rid of those butterfly valves that go bendy if you use them in a warm climate, and those spring-clips that go rusty if you use the unit in the sea. The Dolphin is easier to assemble before diving, thanks to arrows marking the inhalation and exhalation and the direction of the gas flow. The mouthpiece is now colour-coded (red for exhalation, black for inhalation) and all the new screw connections are resistant to the dirt and detritus unavoidable in the real world. The corrugated breathing hoses have been weighted to stop them floating up around your head as they once did. The inhalation and exhalation bags are now made of a durable, reinforced material and have a water drain to make cleaning easier. The fragility of the original bags was always a problem, and even the unit on which I was trained had a split in its exhalation bag suffered in the process of shipping. This design defect was discovered early on (I am TDI DrÃ?ger Rebreather Diver No 004) but it took a long time for the enormous Draeger Corporation to put through these crucial design changes. Again, all the connectors are now colour-coded and dirt-resistant. They are also removable, permitting separate bag replacement if necessary . The scrubber unit has been re-thought - and it needed it. Gone is the cheap, flexible box that lost its shape and hence its ability to stay watertight when it had been over-tightened once too often. In has come a unit made from a far more robust and heavier-looking material, with a lid that fits and an additional sealing frame round the filter. Arrows mark the directions for inhalation and exhalation. Again, the connectors are colour-coded and replaceable, and sealing plugs allow the user to take the unit out of the rebreather and reinstall it later without spilling white powder everywhere. This is naturally subject to duration limits of the scrubber material, which is around three hours if kept dry. You choose a suitable nitrox mix, with regard to maximum operating depth (MOD), and a gas supply port to match. The four gas supply ports, tiny orifices cut by laser, are now colour-coded for the different flow rates. They give rates for 60, 50, 40 and 30% O2 and each is now sealed when not in use by a cover with an O-ring. To my mind blockages of these orifices by salt crystals or other foreign bodies represented the most serious defect and insidious danger of the Atlantis 1. A well-used but badly maintained unit could be delivering a reduced gas flow, with the diver gloriously unaware that he was about to become hypoxic. Thankfully there seemed to be few incidents, but users were exhorted to check flow-rates before diving. They were provided with a rather Heath-Robinson method involving a plastic bag for this purpose, so few ever did check. Now you can, with a simple little US-made flow-meter that gives an instant result. Though the MOD depends on the nitrox mix in the tank, the decompression required has to be calculated from the mix actually breathed in the breathing circuit. So why use a semi-closed circuit rebreather, when it offers none of the decompression advantages of the fully-closed type? Advantages over ordinary open-circuit scuba include using a smaller amount of breathing gas and producing fewer exhaled bubbles. There is also the constant-buoyancy effect, and essential coldwater performance. This last is important to UK freshwater divers and happens because the user rebreathes his gas and does not fill his lungs with masses of cold air freshly decompressed from a tank. Because of the exothermic chemical reaction going on inside the scrubber, a rebreather actually produces heat, and this warms the breathing gas too. Nitrox use is dictated by the size of the constant-flow orifice selected. It doesn't matter how quickly you breathe or how hard you work, every diver has more or less the same gas duration. It's all down to how long it takes for the tank of pre-mixed nitrox, available in 4 or 5 litre sizes, to drain slowly down through the chosen constant-flow orifice. That's more than one hour with nitrox 50. Big men and small women are on a par. Excess gas bubbles off and, although this is in reduced quantities over ordinary scuba, there are still quite a lot of bubbles. However, if you use a rebreather in the company of open-circuit divers you immediately become aware of just how noisy conventional mechanical regulators are. So it isn't the absence of bubbles but the absence of noise that enables you to get closer to skittish animals. The Dolphin is also now available in 'stealth' black. The built-in BC of the Dolphin seems far less bulky than that of the Atlantis 1. This part looks very AP Valves. Weight-pockets are built in. The BC is fed with air from a separate cylinder, which also provides a separate conventional scuba bail-out rig. Constant buoyancy is either a joy or a curse. It depends on how well you get on with this effect. It does mean that changes in depth must be made with circumspection. You cannot adjust your buoyancy by altering your own lung volume, as you can so quickly do with open-circuit scuba. When, back at the beginning, the boys from DrÃ?ger asked me for ideas on improving sales of the Atlantis 1, I suggested that they avoid doing demonstrations in swimming pools, as they served only to reveal the disadvantages of semi-closed-circuit rebreathers (the preparation needed) and none of the advantages. I also suggested that they should improve the quality, drop the price and get a distributor that could give a good aftersales service. They seem at last to have taken my advice, and Apeks now handles the business in the UK. The Draeger Dolphin costs £2450 in white, £2550 in black, cylinders and valves included. Draegersorb costs £84 for 18kg.
Apeks Marine Equipment 01254 692200
Note the recessed exhaust port and colour-coded connections.
The main elements of the unit.
The redesigned scrubber unit is more robust than before