Update: Translation from original AGA journal, translation by Åke Larsson:

Aga dual oxymatic Page 1 of 3
Presently there exists two major kinds of breathing apparatuses for so called light (i.e. scuba) diving, namely air apparatuses and oxygen apparatuses. Air apparatuses supply the diver with air or gas mixtures with a similar composition like oxygen helium mixtures, using a special valve that adapt the gas flow to the divers' breathing as well as the surrounding water pressure. The air apparatuses are frequently used among sports-, professional-, and military mine clearance divers since they are uncomplicated and relatively safe. If one respects the maximum times given in the diving tables for dwelling at a certain depth divers disease (decompression sickness) is avoided and the risk for accident is regarded as small.
AGAs' addition to the plethora of air apparatuses it the AGA Divator, the Divator is renowned for a very low work of breathing. It is undergoing (ständig) development with continuing improvements (see the AGA journal, 1957).
Oxygen apparatuses supply the diver with pure oxygen and a part of the exhalation is returned to a breathing bag after the expelled carbon dioxide has been removed in a filter containing an alkali absorption substance.
The oxygen in the breathing bag can me re-used for inhalation and only the fraction consumed by the wearer during the previous breathing cycle needs to be replenished from the supply of compressed gas. Since all the gas carried by the diver is directly consumed by him, the apparatus will be very economic regardless of the diving depth. In a modified variant of the oxygen apparatus, the mixed gas apparatus, a gas with nitrogen and an oxygen fraction higher than in air is added. The rationale for its creation is the need for a unit with less risk for poisoning than the oxygen apparatus and less risk for divers' disease than the air apparatus. The usage has so far been limited by the fact that the common tables for time and depth are not suitable and that the correct ones have been hard to determine. The oxygen apparatus is used by advanced sport divers down to no more than 10m. The unit is especially suited for combat divers (frog men) primarily due to its long duration and the fact that it does not leave any tell tale bubbles on the surface.

Aga dual Oxymatic Page 2 of 3

The novel oxygen apparatus, the AGA Dual Oxymatic, which is presented here, differs significantly from conventional apparatus by, among other features, the following:
- Automatic oxygen addition that directly supplies the divers' demand
- Stabilized buoyancy
- Automatic compensation of the hydrostatic pressure difference between the breathing bag and the lungs when the unit is used in water
- Low gas flow resistance due to large flow areas
- Hydrodynamically well designed, built-in, breathing bag that also provides some protection of the lungs to underwater detonations.
The Oxygen apparatus AGA Dual Oxymatic is provided with a breathing bag which folds are designed like the bellows of a harmonica. It is suspended between two metal plates, one it the back plate of the apparatus and the other is a movable "klaff". Two fins made out of polyethylene that also has a stabilising effect during fin swimming protect the sides of the bellows. In the breathing bag there is a valve supplying oxygen when the breathing bag is collapsing. A dump valve is mounted in the movable "klaff". The valve opens when a chain fixed to the opposite side of the bellows is stretched which happens when the bellows is full. The diver connects to the apparatus through two separate breathing hoses with non-return valves. A valve in the mouthpiece or the full-face mask allows the closure of the apparatus and makes the expelling of condensate possible under water. The exhaled gas passes through a large (1.7l) absorption canister where the carbon dioxide is removed after which the remaining oxygen is returned to the breathing bag and is available for a new inhalation.

1. Automatic addition of oxygen: If the gas volume in the breathing bag is insufficient gas will be added during the end of inspiration when the movable "klaff" of the breathing bellows activates the addition valve. When the gas in the system is compressed during descent gas is added as well and the buoyancy is maintained constant. During ascent the gas will expand and the addition valve will close until the divers oxygen consumption has reduced the volume of the bellows to the normal volume. Excess gas can escape through the dump valve. During normal diving the diver will not have to bother with the manual addition of oxygen.

2. Stabilized buoyancy: By the help of weights or by the adjustment of the working position of the oxygen addition valve, the diver can adjust the buoyancy so he will be weightless under water. According to recent investigations in the USA. A diver switching from a conventional apparatus to a device allowing the adjustment of the buoyancy as described above, can increase his performance...

Goff, L.G., F. Brubach, H. Sprecht: Measurement of respiratory responses and work efficiency of underwater swimmers utilizing improved instrumentation. J. Appl. Physiol. 19. 197 - 202, 1957.

Aga dual oxymatic Page 3of 3:

...for example with regards to his swimming speed with up to 100%. If the diver needs to temporarily increase his buoyancy, for example to lift heavy equipment, this can be done by the addition of extra oxygen using a manually operated valve. The apparatus can be used as a floatation device on the surface by filling it with air from the lungs.
3. The breathing bag and the lungs will in some cases be at different depth. This will result in a pressure difference between the bag and lung which in conventional apparatus will act as a breathing resistance and will significantly reduce the working capacity of the diver. The breathing bag is best placed on the divers' back. In the normal swimming position there will be a relative under pressure of about 20cm water column. During hard physical work, when the heart and lungs are exposed to stress, this under pressure might cause acute heart dilatation. In the novel design these problems have been eliminated by the addition of a counter weight on the upper movable (klaff). This will create an over pressure of 20cm water column in the breathing bag in the normal swimming position. Also in other swimming positions the pressure differences in the breathing system will be compensated. This gives the possibility to replace the common mouthpiece with a less tiring inhalation mask without risk for leakage. This simplifies the use of a full face mask which will reduce the discomfort associated with swimming in cold and dirty waters. A well functioning pressure compensation is also depending on the proper positioning of the breathing bag in relation to the lung. The carrying harness and webbing fur fills this requirement without limiting the divers' freedom of movement.
4. Low flow resistance: In devices designed for conducting gases of high density the hoses and flow paths have to be made especially wide.

Åke: Thank you for translating the Swedish AGA Journal for me, Janwillem