
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. 

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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 semiclosed
equation: 



The meaning of the formula is: 



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.

FiO2 = unknown

Qs = 3,0 ltr/min

FsO2 = 0,5 (EAN 50)

VO2 = 0,5 ltr/min

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..


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:


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.


In the
following manual you find more details about this very
nice unit! 

































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
08092010 