Easiest breathing CCR.

[Mr.X]

Ok. Just for the heck of it - In your opinion what is the easiest breathing rebreather?

IMO - the Megalodon with neoprene counterlungs is pretty darn nice. Prism too. After that, they all sort of fall in the OK range for OTS lungs. Ballistic nylon certainly has more resistance. This would include the Insp., CIS, regular Meg. etc.


X

 

[silent running]

Ok. Just for the heck of it - In your opinion what is the easiest breathing rebreather?

IMO - the Megalodon with neoprene counterlungs is pretty darn nice. Prism too. After that, they all sort of fall in the OK range for OTS lungs. Ballistic nylon certainly has more resistance. This would include the Insp., CIS, regular Meg. etc.


X

Hi X, while neoprene may add something like assistance on the inhale and keep their shape more open, even with min loop volume, all of this probably falls under the "perceived" WOB category. I know of no hard testing that supports neoprene lungs having lower WOB on the same loop as cordura, do you? Also, it's harder to clean neoprene lungs and I have been told that they are easier to rip and generally less tough.

As for other WOB variables, axial scrubbers with their typically longer grain boundaries, will always add to WOB as compared to a radial, with it's shorter grain boundaries. This helps explain why the AP CCRs test higher for WOB than other OTS units. It's probably also a function of their flapper valves being thicker than say the Prism. AFAIK, the Prism has the lowest WOB of any CCR tested by the USN-1.6 J/L. As for the CIS, I believe there is test data somewhere that shows the hydrophobic scrubber membrane brings the WOB up significantly. Supposedly Boris is slightly lower than the Prism, but it has big diameter hoses and as with all BMCLs, the WOB probably differs quite as lot as one moves through different body positions, which is one of several reasons why I'll likely never dive a BMCL unit ever again... -Andy

 

[wedivebc]

Having only dove dolphin, sport kiss, inspo, and meg with both neoprene and nylon CLs I have to say the meg with nylon CLs work best for me. I have pretty big lungs and the neoprene don't have quite enough volume for me.

 

[ScubaDadMiami]

Part of the answer to this is variable because packing the canister is an art, and there is no duplication from fill to fill. Second, as the dive proceeds, the scrubber expands as it picks up moisture, increasing the work of breathing.

Then, there are the differences between designs. OTS counterlungs breathe better in most positions compared to most backmounted counterlungs. Positioning of the diver also affects the WOB.

The thing I like about the Optima is that the diver will have a consistent result, time after time, by using the Extend Air Cartridge. The WOB does not change over the course of the dive from pellet expansion. The canister is horizontal, and it is located just behind the diver's neck. This provides a shorter loop overall, which takes less effort to push the gas all the way around it, and it allows for smaller diameter hoses without increasing the WOB while maintaining comfort during the dive apart from the WOB.

In the end, all of the major players breathe well enough though some are better than others by virtue of the inherent characteristics of the design (OTS versus backmount). As far as jules measurement goes, I can't tell you the specifics. But, I am very happy with the way that my Optima breathes.

 

[vtach]

I am really happy with the WOB of my Sentinel in most positions. Head down seems to have the highest WOB but it is still far from sucking through a straw. I completed MOD 1 this spring so I have relatively limited experience with multiple units. I have tried a few different ones (Inspo/Evo, KISS, Meg, Boris) in the pool setting and I still think the Sentinel breathes easier, but as already mentioned, it is probably far from being entirely objective. One dislike I have with the Sentinel is the length of the breathing hoses. Damn are they long. I wonder what difference a shorter length hose would make for WOB. I think the CL is large enough so that taking some length out of the hose might not make a drastic difference in loop volume. In time...but for now I will keep it relatively unmolested.

 

[sunnyboy]

Part of the answer to this is variable because packing the canister is an art, and there is no duplication from fill to fill. Second, as the dive proceeds, the scrubber expands as it picks up moisture, increasing the work of breathing.

Then, there are the differences between designs. OTS counterlungs breathe better in most positions compared to most backmounted counterlungs. Positioning of the diver also affects the WOB.

The thing I like about the Optima is that the diver will have a consistent result, time after time, by using the Extend Air Cartridge. The WOB does not change over the course of the dive from pellet expansion. The canister is horizontal, and it is located just behind the diver's neck. This provides a shorter loop overall, which takes less effort to push the gas all the way around it, and it allows for smaller diameter hoses without increasing the WOB while maintaining comfort during the dive apart from the WOB.

In the end, all of the major players breathe well enough though some are better than others by virtue of the inherent characteristics of the design (OTS versus backmount). As far as jules measurement goes, I can't tell you the specifics. But, I am very happy with the way that my Optima breathes.

Good summary (though I have no Optima experience to comment).

However, don't forget the scrubber orientation - axial vs. radial and the many variations. In general, the same quantity of scrubber material will breath easier in a radial scrubber vs. an axial scrubber, other things being equal.

Also, for a radial scrubber (I dive a Prism), you can pack the scrubber quite a bit "tighter" and still have very easy WOB thanks to the radial design.

Cheers,

-S

 

[Mr.X]

Thanks guys for the terrific responses. It's a good dialog about all the variables that go into RB breathing resistance, both objectively and subjectively. I will say that from my experience with the mid 2000 RB (Insp. Cis, Prism, Meg, etc) the OTS lungs which are located near the centroid make for easier breathing. That being said, I have never really had much of an issue with CL's backmounted, belly mounted etc. In fact, my favorite RB is the LAR V single "bagger."

As the neoprene lungs...I used the late Will Smither's early Megalodon (trimix enabled 1st version APECS) and I loved them. They were however, very delicate, floatier and predecessor to the current MEg CL's. Additionally, the CIS Lunar MK 5p was noticeably a harder breather than the most of the OTS breathers I have used. Lots of factors involved in that. Someday, it would be interesting to see if some manufacturer could use a non-corrugated breathing hose (molded, or non-kinking) and a combination of mushroom valves that opened like feathers, but closed tight like a iron door.

Cheers

X

 

[silent running]

Also, for a radial scrubber (I dive a Prism), you can pack the scrubber quite a bit "tighter" and still have very easy WOB thanks to the radial design.

Cheers,

-S

Yes s, I have never noticed any increase in the WOB of the Prism radial, even after 10 hours. I don't think the grains expand that much after being activated and more importantly, the surface area of an in to out radial increases from inside to out, which means there are also more voids and thus less resistance as the gas travels out word.
The downside is that breakthrough can happen faster in a radial, but I would still take lower WOB throughout the life of the scrubber in exchange for the possibility of something that can only happen if we push the scrubber really long... -Andy

 

[padiscubapro]

Hi X, while neoprene may add something like assistance on the inhale and keep their shape more open, even with min loop volume, all of this probably falls under the "perceived" WOB category. I know of no hard testing that supports neoprene lungs having lower WOB on the same loop as cordura, do you? Also, it's harder to clean neoprene lungs and I have been told that they are easier to rip and generally less tough.

As for other WOB variables, axial scrubbers with their typically longer grain boundaries, will always add to WOB as compared to a radial, with it's shorter grain boundaries. This helps explain why the AP CCRs test higher for WOB than other OTS units. It's probably also a function of their flapper valves being thicker than say the Prism. AFAIK, the Prism has the lowest WOB of any CCR tested by the USN-1.6 J/L. As for the CIS, I believe there is test data somewhere that shows the hydrophobic scrubber membrane brings the WOB up significantly. Supposedly Boris is slightly lower than the Prism, but it has big diameter hoses and as with all BMCLs, the WOB probably differs quite as lot as one moves through different body positions, which is one of several reasons why I'll likely never dive a BMCL unit ever again... -Andy

Andy,
remember you can't directly compare the "1.6j" number against alot of the other rigs.. So please stop trying to give this impression.. The numbers quoted by alot of other rigs use a totally different test scheme, and their numbers must include the simulated WOB of the diver..
I don't doubt the Prism breaths well, but the numbers are not that much better than many rigs...

also rigs that are tested to CE spec are tested in the vertical position, not the prone position that the PRSIM was tested in.. for most rigs the numbers are less (some significantly) in the prone position, but since the vertical is the worse breathing position for most designs, its the one that has to be tested to..

 

[silent running]

Andy,
remember you can't directly compare the "1.6j" number against alot of the other rigs.. So please stop trying to give this impression.. The numbers quoted by alot of other rigs use a totally different test scheme, and their numbers must include the simulated WOB of the diver..
I don't doubt the Prism breaths well, but the numbers are not that much better than many rigs...

also rigs that are tested to CE spec are tested in the vertical position, not the prone position that the PRSIM was tested in.. for most rigs the numbers are less (some significantly) in the prone position, but since the vertical is the worse breathing position for most designs, its the one that has to be tested to..

Hi Joe, yes I'm aware that comparisons are difficult, given the 2 differing test protocols, that's why I qualified what I said by referencing the USN tests specifically. I'm not trying to give any impression other than the facts as they are documented in the NEDU test data, as I said. So please stop giving the impression that I'm trying to give some impression other than what I posted.

But since you brought up the subject of cross test comparisons, please remember that Alex Deas bothered to include the Prism in a WOB chart on an RBW thread, after making adjustments for internal diver WOB and the deeper NEDU test depth in the calculations and the unit still came out with lower WOB than all except Boris. I don't take it as fact, but those were Alex's calculations not mine and he is a stickler for detail of the highest order. The NEDU Prism tests also include a hydrostatic load measurement for both prone(.47kpa average) and upright(-.09kpa average), both of which exceed their 1.0kpa test criteria. And if I understand the figures correctly, the hydrostatic load is actually higher in the prone position, the opposite of Boris and which might be another reason why the NEDU WOB tests are done in the prone position, other than divers typically working hardest while swimming... -Andy