Extendair better for flood recovery?

AD_ward9

I would still prefer an EAC, because there is far less of an increase in WOB as the scrubber becomes exhausted, and it is simpler.

The increase in breathing resistance with damp or exhausted granular scrubbers can be quite considerable. Remember if a hydrophobic membrane is used, it keeps water in, as well as keeping water out. That is not a wonderful thing with granules.

Alex

diverklondike

Toooo funny.... I was going to add that but the phone rang and I just hit submit with the intent to edit it... lol... Absolutely correct! But at 2,000 usd per, it better keep the kitty litter dry!

trob09

I guess the obvious question is do you have empirical data that validates the Cis can's increase in WOB? In anecdotal, non-scientific experience, I have not noticed any increase in WOB.

While I concede that installation of an EAC is simpler than filling a Cis can, the supply logistics make it less attractive for me (as has been covered previously, along with my environmental concerns)

T

trob09

When I look at the horrendous amounts of money I spend every year on insurance, a one-time $2k expense seems a cheap insurance policy to me...

n2diving

The plastic has no negative effect in practice, and certainly no more negative effect than the inert binders used in granular. The cartridges are actually very efficient and this has been documented in published data.

-- Mark

AD_ward9

Anecdotal experience comes up many times when people talk about breathing resistance. The fact is the lungs are really bad at measuring breathing resistance. We use a breathing machine, and in every case we have ever measured granular scrubbers we have always seen an increase in WOB as the scrubber is used.

We have published a report on the effect of flooding a granular scrubber, with as little as 100ml of retained water causing the WOB to increase four fold (the second report in the list HERE). Most granular scrubbers have the same sort of increase. One just has to look at the swollen and caked together material after the dive to see that the resistance is going to be higher than when freshly packed, but the breathing machine measurements in the report quantify it.

Alex

schford

I was informed that the increase in breathing resistance with used sorb though was negligable compared to the work of breathing resistance caused by elbows and the gas changing direction and the like..

That is to say when you measure the Work of Breathing for the whole loop not just the scrubber the impact of the used material is minimal as the work of breathing caused by the scrubber is minimal compared to that caused by gas changing direction in the loop, one way valves etc.

Have you tested the impact with the whole loop or just the scrubber - if so is what I got told right as it makes sense...

__________________
Bailout and Kit Management account for Murphy's Law

The only bad question is one you did not ask and later wish you had.

Use of Rebreather World is subject to the Rebreather World Terms & Conditions of Use

trob09

Thanks for the data reference, I'll take a look. I am aware that anecdotal evidence is a poor judge (hence my "non-scientific" description). BTW, swollen, caked together sorb is also anecdotal...

I guess the next question is (following in Stuart's line of thinking) is 4 fold meaningful? While I am no statistician, I do manage a team of them and am well aware that percentile numbers can be misleading if misread or used inappropriately. 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...)?

AD_ward9

The report is quite careful to separate out each component in the WOB, or more accurately, peak breathing resistance. That is, the resistance of the hose, of the connection etc, is measured first.

The gas changes direction almost sinusoidally, so there is almost no WOB in stopping the gas flow and reversing it.

It can be seen from the report that the scrubber resistance is many times that of the hoses, and the scrubber resistance in that case increases up to four times when wet (with as little as 100ml to 150ml of water).

The same experiments done with an EAC give less than 10% increase in breathing resistance (generally 5%, but depends a bit on the wrap). With EACs, the resistance is very much lower than for granular material, unless one uses an impracticably wide scrubber geometry, and has no perceptible increase in WOB after a flood.

Alex

AD_ward9

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