Manual Version 19 / 01-2019 II Page 9 of 44
SF2 ECCR OPERATION MANUAL
Since we can only
breathe in a circuit if
the gas has a flexible
volume in which to
collect it, in our body
that flexible volume is
the lungs. The SF2
has a "counterlung" in
the form of a bellows.
This type of
counterlung
configuration is unique
in the rebreather world
and has various
advantages: It is
compact, easy to
assemble, protected
by the lower carbon
tube. Last but not
least, an important
feature of the
counterlung is a huge
water trap at the
lowest point of where
the pressure relief
valve is located.
This describes the most important components of the SF2 and a rebreather in
general. The only thing missing is the gas addition supply. As mentioned at the
beginning, the consumed oxygen is added back to the system in pure form. The SF2
has an oxygen cylinder which, again from the perspective of the diver, wearing the
device located on the divers’ right side. Pure oxygen becomes "toxic" from a depth of
about twenty feet (six meters) and can no longer be breathed safely. So the oxygen
has to be diluted. In English this is called dilute and that is why the term diluent bottle
has established itself. Two gases are used as diluent in the SF2: On the one hand,
normal air and, on the other, trimix mixtures, i.e. a gas consisting of oxygen, nitrogen
and helium.
The diagram on the next page gives a good overview of the structure of the SF2
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