padiscubapro:
For overall breathing confort on an OTS design the location of the scrubber really has little effect on the overall breathing resistance.. The dead spaces have no effect on the WOB, the path through a scrubber does..
On an OTS design your getting your gas from the inhale counterlung and as long as sufficiend volume is present you arent going to notice any problems taking a breath (remember its at a greater pressure (normally) than your mouth so there should be little effort inhaling).. for what we perceive as easy breathing its the inhale that it important, we really dont notice small changes exhale breathing resistance, but inhale resistance we do feel..
Believe it or not the BIGGEST contributor to WOB in general is the DSV..
If length of gas path was that critical a radial design would actually be a bad thing since that would mean that the furthest points wouldnt be getting the same shot at the gas and the shortest portion of the scrubber would be geting all the work, therby a short duraction, which isnt the case.. The part inside the fixed container is all at the same potential..
The big thing to remember about the meg esespecially is that there is alot of open space for the gas to freely flow to the scrubber opening.. The resistance to flow is going to be much smaller than having to supply the scrubber from a small tube..
Hi Joe, thanks for the detailed post. I am aware that DSV is a big part of the overall WOB, however, barring a really badly sized one relative to the rest of the design or too thick mushroom valves, I'm not sure it's as big a factor as other things combined. And I think I agree with you that what happens inside the scrubber all has the same hydrostatic potential, but I was actually trying to point out something else having to do with how the gas enters and leaves it, and how this relates to the asymetry of the tidal cycle. Sorry if it was confusing, I couldn't get a hold of anybody from SMI to confirm this, so I have to go by my memory of the explanation of loop dynamics. Please bare with me as I try to put the the thought into words...
Yes, the path inside the scrubber is a big issue. But that's exactly why I would have hard time believing that an axial scrubbber, which has a longer-6 to 7 inch-path through the sorb, would breathe easier than a similar sized radial, which has a shorter-2 to 3 inch-grain boundry. If I'm not misremebering, the scrubber itself is a kind of boundry btw the inhale and exhale cycles, which are not equally forceful. And this would then be very important to the loop layout...
Both the axial Meg and the Prism have spaces all around the scrubber that the gas flows through. In the axial Meg, the gas enters through the scrim in the bottom of the scrubber, which in the breathing cycle, would be powered mostly by the exhale, the stronger part of the tidal flow. It then exits through a tube/restriction at the top, which would be drawn out mostly by the inhale part of the tidal cylcle, the weaker part. This is still an improvement over the Inspo, in which the inhale has to pull the scrubbed gas out the bottom of the scrubber, down through the restictive, lower elbow and pipe, up to the inhale CL. I still think that there is additional, if slight, hydrostatic loading anytime gas winds up going lower than your lungs as surely the down pipe/elbow on the Inspo does, in a normal slightly head up dive position...
But in the Prism, the gas enters the scrubber through the radial center tube during the stronger exhale cycle and has only to travel through the shorter, radial grain boundry, before hitting the large outer space around the scubber, where it is drawn up into the inhale CL on the inhale cycle. In the Prism the gas path is, I think, better matched to the asymetical tidal cycle-stronger exhale pushes the gas through the front smaller, more restrictive part of the loop, weeker inhale draws from larger, scrubbed resivoir around the scrubber. If this is true, then it means that a radial with an outside to in flow would not bbreathe as easy as the into out, as the inhale would be drawing from the the most restrictive part of the loop-the center radial tube...
I hope this makes more sense, -Andy
