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AD_ward9 · 24th April 2007, 05:57

Quote: (Originally Posted by trob09)

I've always heard that the greatest contributor to WOB is in the flapper valves of the DSV...

Lastly, if swelling of sorb creates additional WOB, what are the statistics for the EAC as it is used or if it gets wet (noting that statistical values are often irrelevant without comparisons...)?

First the flapper or mushroom valves. The biggest restriction is actually the mouthpiece orifice, followed by the flapper valves, unless the flapper valve has been really badly designed. The mouthpiece and flapper cross section can be increased to around 7 to 10sqcm each. A granular scrubber has a far higher breathing resistance: so high it usually requires two breathing bags to even out the peaks and spread the flow across the whole breathing cycle.

Moving onto your EAC question: there is a 5% increase in breathing resistance across the EAC after putting an EAC into warm water for 5 minutes, then allowing 30 seconds to drain and put back into a canister.

It is difficult for me to convey the huge difference in WOB between well designed EAC systems and granular. The systems out there using EACs right now have various design limitations that give a warped perspective. Breathing machine figures I quote need to be translated into a feeling for divers to understand just how powerful EAC technology is.

Last week nine divers, who were among the most experienced commercial divers alive today, were flown into Bergen to test a twin scrubber rebreather at the Norwegian State Dive School. All were experienced on at least one other rebreather using granules.

The EAC unit had no perceptible work of breathing, and was reported by the divers to be "100 times or even 1000 times better WOB" than the granular system, and lower WOB even than surface supplied gas.

I tried it immediately after a short stint as a safety diver in the tank, using a finely tuned Cyclone and a newly serviced Jetstream: the EAC unit had a much lower WOB than either the O.C. regulators. I have never noticed that using granules. There was just no apparent WOB.

In fact, breathing resistance was so low, divers were using a hard hat with an oro-nasal mask that did not contact with the face and no mouthpiece, yet did not suffer from CO2 retention during their dives, albeit fairly shallow. Now try that trick with granules ..

I honestly believe EACs are both much safer than granules, and provide the platform for a much higher level of performance than divers are used to.

Alex

24th April 2007, 05:57	#20 (permalink)
AD_ward9 Apocalypse CCR Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,001	Re: Extendair better for flood recovery? Quote: (Originally Posted by trob09) I've always heard that the greatest contributor to WOB is in the flapper valves of the DSV... Lastly, if swelling of sorb creates additional WOB, what are the statistics for the EAC as it is used or if it gets wet (noting that statistical values are often irrelevant without comparisons...)? First the flapper or mushroom valves. The biggest restriction is actually the mouthpiece orifice, followed by the flapper valves, unless the flapper valve has been really badly designed. The mouthpiece and flapper cross section can be increased to around 7 to 10sqcm each. A granular scrubber has a far higher breathing resistance: so high it usually requires two breathing bags to even out the peaks and spread the flow across the whole breathing cycle. Moving onto your EAC question: there is a 5% increase in breathing resistance across the EAC after putting an EAC into warm water for 5 minutes, then allowing 30 seconds to drain and put back into a canister. It is difficult for me to convey the huge difference in WOB between well designed EAC systems and granular. The systems out there using EACs right now have various design limitations that give a warped perspective. Breathing machine figures I quote need to be translated into a feeling for divers to understand just how powerful EAC technology is. Last week nine divers, who were among the most experienced commercial divers alive today, were flown into Bergen to test a twin scrubber rebreather at the Norwegian State Dive School. All were experienced on at least one other rebreather using granules. The EAC unit had no perceptible work of breathing, and was reported by the divers to be "100 times or even 1000 times better WOB" than the granular system, and lower WOB even than surface supplied gas. I tried it immediately after a short stint as a safety diver in the tank, using a finely tuned Cyclone and a newly serviced Jetstream: the EAC unit had a much lower WOB than either the O.C. regulators. I have never noticed that using granules. There was just no apparent WOB. In fact, breathing resistance was so low, divers were using a hard hat with an oro-nasal mask that did not contact with the face and no mouthpiece, yet did not suffer from CO2 retention during their dives, albeit fairly shallow. Now try that trick with granules .. I honestly believe EACs are both much safer than granules, and provide the platform for a much higher level of performance than divers are used to. Alex Last edited by AD_ward9 : 24th April 2007 at 13:28.
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