Quote: (Originally Posted by
Guilhem)
FWIW, the submatix mCCR also inject O2 in the inhale lung. Their answer to the often-asked question is at the bottom of their
FAQ page. It does lack hard numbers though.
An often asked question is why the oxygen is feeded at the ADV and not in the scrubber tank at our CCR rebreather.
An explanation of the most important reasons you will find in the following:
As argument for a feeding of the oxygen in the scrubber tank a better mixture of the oxygen with diluent is named. In principle the thought that the oxygen has to be mixted up with diluent is right. When oxygen is feeded to the ADV, oxygen is mixed up immediately with diluent through the gas flow. This will happen while every breathing.
Explanation:
In the breathing circulation about 10 litres of breathing gas are existing. Through breathing this gas moves permanently (at a calmly breathing about 10 breathes per minute). In this permanent moving about 1 litre oxygen per minute is feeded to the system through the constant flow. Through the moving of the breathting gas the oxygen is mixed up constantly with the gas of the breathing loop. The result will be a constant mixing of the oxygen with the diluent. This is confirmed through large-scale measurings.
At a feeding of oxygen in the scrubber tank the oxygen is also mixed up with diluent. But the problem will be the danger of hypoxia in the case of a streamed scrubber tank.
Example:
For any reasons the scrubber tank is streamed. The diver will recognize the symptoms and end its dive. When he/she changes now to the bailout system, no problem will arise. But when he/she further breath from the rebreather, the following problems will arise: Through water in the scrubber tank, the gas flow is interrupted and the bypass will response at every breath. When the diver starts the dive to the water surface now, the gas expands in the system and the bypass do not deliver any fresh gas. This means that he/she breathes only diluent. If the used diluent is compressed air or in the worst case trimix, a black out will arise through hypoxia. The result will be an accident in flat water.
While the feeding of oxygen in the ADV this possible problem is ruled out.
1. This discussion was towards me considering a MEG as a second unit. Submatrix is not an option I want to entertain.
2. You can not compare one manufacturers explanation to another.
3. It even states that the fact that the O2 needs to be mixed and dispersed as "correct thinking" then goes on to justify the fact that it is okay because it is mixing with 1 liter of air rather than 10 liters. With simple math, anyone can see that a shot of 100% O2 is far more concentrated in 1 liter than the same shot dispersed in 10 liters.
4. It seems to me that by saying that you "need the high O2 the most when you low" seems a little far fetched. If you have enough cognitive function to have the mental aptitude to switch off the loop, or add O2, you have plenty of time to live and breath as little as .21 or anything that is not hypoxic. If that theory was correct; (this is a stretch, I know
) then, why would you want just breathable gas on your bail out and not pure O2 or 80% O2, after all, thats when you need it the most and that is what you get with an O2 slug?!
5. Lastly, this is a question from other previous initial posts. If I understood this right, you can switch the O2 to the exhale CL? is this correct? If so, that seems like a viable option for someone.
i am just trying to figure this out, so when I retire the Evolution to the wife when she is ready to switch to CCR I will know what I want for a second rig.
regards,