| Recently I was able to buy a Dräger Tauchretter Model TR 60. This life saving dive jacket was designed in the 60's and is a surprising rebreather. One of the most interesting aspects of this rebreather is that in fact it is a semiclosed rebreather! It is well known that using pure oxygen rebreathers to escape from depth introduces a big risk of oxygen toxicity. Semiclosed rebreathers offer a improvement because the breathed gas has a much lower oxygen content. This rebreather uses EAN 50! | ||||
| The TR 60 is a very complete and well designed compact rebreather. Please check the Gallery for photos. | ||||
| è GALLERY ç | ||||
| To understand how the rebreather works on depth I here made two calculations to show why the partial pressure of oxygen is much lower with a semiclosed rebreather compared tot the standard oxygen rebreathers. The working principle is based on the semi-closed equation: | ||||
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| The meaning of the formula is: | ||||
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The unit is equipped with a constant mass flow regulator with a gas flow of 3,0 l/min. This flow is constant to a depth of 40 meter. This means that the intermediate pressure is 10 bar on the orifice. The flow will continue to 10 bar and the stops. This will happen o a depth of 90 meters. Becauese the flow is constant to half the IP at 40 meter there will be exact 3,0 ltr/min. Imagine a diver who uses 0,5 ltr oxygen per minute the partial pressure he is breathing can be calculated with the mentioned equation. |
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FiO2 = unknown |
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Qs = 3,0 ltr/min |
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FsO2 = 0,5 (EAN 50) |
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VO2 = 0,5 ltr/min |
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FiO2 = ((3,0ltr/min x 0,5)-0,5)) / (3,0 ltr/min - 0,5 ltr/min) = 0,4 meaning the fraction of the inhaled gas is 0,4. The gas is EAN 40 breathed at 40 meter the partial pressure of oxygen at depth is 5 bar ambient pressure x 0,4 bar oxygen pressure = 2 bar ! In the 60's military divers where supposed to be capable of breathing 2 bar oxygen! Fortunately this has been changed, although this unit would only be used in a emergency situation and therefore the 2,0 bar is not so crazy.. |
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When the diver uses more oxygen due to swimming or stress the unit can be used deeper. Imagine a oxygen consumption of 0,8 liter per minute the inspired gas is: |
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FiO2 = ((3,0ltr/min x 0,5)-0,8)) / (3,0 ltr/min - 0,8 ltr/min) = 0,318. When a gas is breathed with a fraction of 0,318 th maximum depth when 2 bar oxygen pressure is allowed is 2bar / 0,318 = 6,28 bar. On a depth of 52,8 meter the rebreather feeds EAN 31,8 resulting in a oxygen pressure of 2bar. |
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| In the following manual you find more details about this very nice unit! | ||||
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| For additional pictures please check the GALLERY | ||||
| I would like to thank Joe Brandt for his kind cooperation sending me the manual and info about this great unit. Please check Joe's website here | ||||
| If you have additional information, pictures or information about this unit please do not hesitate to send it to: jw.bech@quicknet.nl | last modified 08-09-2010 | |||
