Quote: (Originally Posted by
trob09)
Alex, My points are this:
- Tests need to be made with a full, actual rebreather to determine if the change in WOB is relevant (i.e. is 5% or 4-fold relevant when all components are in place or are those statistics irrelevant due to other factors that define WOB but are excluded from your bench test?)
- "Can be determined by simple arithmetic" is not empirical data
Using the empirical data to get to the result you want without having to do an infinite number of experiments. If something can be calculated easily, then there is no point wasting tons of money on experiments. One does one set of experiments very carefully, gets the empirical data, then use well established laws of physics to calculate the other cases. The cost of these experiments is so high, I do not see lots of people on here repeating them and publishing their own results (alas).
Quote: (Originally Posted by
trob09)
- Soaking for two hours and then left to drain does not reflect what might occur in a loop flood. After 2 hours, I'm going to be on the surface.
You are right that there are a number of different experiments that can be done.
The particular experiment reported was to find the effect of flooding on a recovered rebreather. In most rebreather accidents, the mouthpiece falls out of the mouth (even though EN14143 requires a mouthpiece strap), and the unit floods. There is then a forensic need to work out from the flooded rebreather what state it was in before the flood.
However, we picked the 2 hour time because it is a good rebreather dive time. The loop is almost fully humidified and water is retained by the scrubber. This causes caking very similar indeed to that of immersing the scrubber in water. We measured the amount of retained water and it is less than the amount of water the scrubber generates by absorbing CO2 during a 2 hour dive.
Quote: (Originally Posted by
trob09)
I am _not_ saying you are wrong or that the EAC is inferior. I am saying that clear superiority has not been established to the degree I seek. As such, it remains a "nice idea" for me but also carries drawbacks that do not exist with granular sorb.
The only drawbacks we are aware of are supply, cost and much lower tolerance for poorly designed scrubber gas flow.
The issues you raise are relevant, but is really up to vendors who use granular material to carry out these tests and publish the results to justify the safety of their systems under foreseeable conditions. We have published sufficient data and explain our views (and we accept there may be valid alternative views), that granular scrubbers do not seem to meet the safety requirements for SIL 4 operation in a diving rebreather.
Quote: (Originally Posted by
trob09)
I don't mean to demean your work, but the data I am asking for is not in the report you reference. I don't believe it exists in a true apples-to-apples comparison.
Sorry, but I must disagree with the method you propose.
To compare the breathing resistance of scrubber A to scrubber B, we measure each scrubber, and eliminate all other parameters.
If you put scrubber A in rebreather X and then scrubber B in rebreather X, you introduce lots of other parameters that are simply noise. You get a result that is valid for rebreather X under the test conditions but nothing else.
The rebreather is a linear system.. If one component that is 80% of the total breathing resistance increases its resistance 4 fold, then the breathing resistance of the rebreather will increase by around four fold. If you want to go from this first approximation of the performance of the system to a much more exact number then you can do it either by calculation or by expensive measurements.
We have published a very details maths model of a rebreather, using which it is easy to put in the parameters of your loop, put in the resistance of the scrubber, and it tells you the total breathing resistance. The resistance of hoses etc, is very simple to measure and to model. There are only 4 gas laws involved.
Alex