I wrote in which the family moves SCR. I know that it is not widely known SCR 3 family.
1 CMF (Constant Mass Flow) we have a small hole through which the filtered solid mass medium such fresh breath. Such a system is extremely simple. Known structures in this class is a Draeger FGG, Dolphin, Amphora.
2 CVR (Constant Volume Ratio) system which is a permanent part of the volume is changed circulation. Examples are DC 55, OXY MIX Crabe, RB 80 and clones.
3 CMR (Constant Mass Ratio) very poorly known in the world recreation of family semi-closed circuit. It is based on the following property in constant ventilation counted consume solid mass of oxygen (the basis of physiology to the efforts of medium and large for most people).
How does it accomplish?
The AGA is currently Interspiro this direction design is developed for decades. In the first embodiments, the mechanical counting was used bellows respiratory movements. After counting to a specific dose level was released regenerating fixed-size mass.
How to realize such a dose?
Feed the little bottle stable hypertension in relation to the environment. in the bottle is stored in hypertensive agent dp breathing cylinder has a fixed volume V.
The product of dp * V is constant for at any depth. Simple.
Implementation of the most unfortunately more complicated mechanically.
http://rebreathers.pl/forum/download.php?id=83
http://rebreathers.pl/forum/download.php?id=82
(Next big step DCSC)
I deal with further expansions to constant ppO2 SCR, necessarily counting ventilation is used.
rc greet