Hi Brad, I know you say this, but the WOB of the Apocalypse is achieved with a cartridge scrubber, which however well implemented in the design, still carries with it the risk of CO2 bypass at high RMV. If you care to explain exactly how your cartridge scrubber design avoids this remarkably bad feature, as opposed to the Optima or Poseidon
In the first place, what CO2 bypass?
www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf
Note that DL scrubber duration's are quoted at the mouth at 40RMV; however, DL have done significant tests up to 90RMV. You’ll get breakthrough sooner but inline with expectations. You’ll note OSEL are the only rebreather manufacturer selling the kit to test this having needed to develop it in-house.
www.opensafety.co.uk/files/Datasheet_iBreatheMkIV_1906.pdf
Optima’s WOB is through the roof and because there was effectively no test and evaluation done on the placement of the EAC in it, you get a lot of negatives that are simply not experienced on any of DL designs, Apocalypse inclusive. You also miss out on the positives, such as low WOB, high scrubber duration, non-water blocked O2 cells and mitigated caustic cocktail risk enabling full flood recovery.
Poseidon used the worst of both worlds with a disposable granular scrubber. ie. not an EAC.
However on the note of CO2 bypass, while a little esoteric for this forum as it drills down into the variation of flapper design specification, it was an issue that DL discovered at 100m in a number of DSV/BOVs that they trialed for comparison against the ALVBOV. After first finding the issue in the prototype ALVBOV before any were sold.
http://www.deeplife.co.uk/or_files/Fault_Study_CO2_Bypass_110314.pdf Sorry for folks not diving an ALVBOV but you’ll have to refer to your individual DSV/BOV manufacturer for a copy of their own testing to verify lack of this CO2 bypass issue.
The shape is odd and it looks obtrusive. I have also read it is heavy and needs to be sent back to the factory for service...
The shape is odd, has to be to get the low WOB and avoid free flow in high current amongst a few other features like the one finger spring triggered bailout. And necklace that bails the loop to OC mode if you remove the BOV to talk on the surface, which is an amazingly common issue that has caused a few units to flood. As a complete system, it is probably lighter than most breathing loops, as you will note the lack of any need for hose weights and a reduced overall loop volume, due to the significantly shorter breathing hoses. The commercial diving version has stainless steel tubes and that is heavy!
When dived the only bit you see is the tip of the bailout lever, which just intrudes into line of sight. Like a modern car bonnet the top of the BOV just slopes away out of sight.
The need to return it for factory service is an interesting thing. OSEL have some customers who return it religiously annually for service, some whom do it every three years with their Apollo A320 1st stages for service, a couple whom noted a minor issue after 7 years and wanted it looked at and a decade later there are a number we know are being regularly dived that have never been back for a service.
Every ALVBOV goes through a pretty exhaustive 5 day pre-shipping routine before shipment, with every parameter tested and recorded and I think that goes a long way towards resolving a number of issues. The couple of ALVBOVs that have been returned with an issue to date have all been sorted out FOC under warranty. It also gets shipped out with all hoses and fitting included as standard.
Flip the coin though and compare a counterlung swap between an Apocalypse and a rEvo…. One takes about 5min and doesn’t need tools! And OSEL will happily sell you as many spare CLs as you desire. Same for user serviceable spares on the ALVBOV.
the shrimp doesnt do that.
No diaphragm problems on my divesoft
Whilst breathing off an independent OC gas supply, try going for a dive on your rebreather down to 10m, with the IP gas supply to the BOV isolated!
You might be unpleasantly surprised what the diaphragm looks like afterwards……
Whilst folk don’t plan to descend with their bailout isolated. It does happen.
Is this "gag strap" a revo thing? Once again, I am new to this, but I have not seen a single gag strap in use anywhere and it wasn't something covered in the purchase or training of my rebreather.
The rEvo is the only sport diving CCR that I know of that comes with one. But, I am certainly no encyclopedia of CCRs.
I was pretty resistant to using one, but my instructor required it for my initial training. It can be annoying on the surface. But, I do find that it is more comfortable in the water to not have to make ANY effort to keep the mouthpiece in my mouth. For that matter, my pre-breathe is more comfortable with the head strap on, too. And then there are the potential safety benefits on top of that.
Stuart, You obviously had a good instructor!
AFAIK the OSEL Apocalypse Type IV CCR and the Mares rEvo are the only sports rebreathers sold with gag straps. Despite it being a CE certification requirement since 2003. Required as a means to prevent the diver drowning and the set flooding in event of the diver becoming unconscious. Paul Haynes wrote a really good academic paper on this, that I linked towards the start of the thread.
The rEvo came with a gag-strap because the first ones used Drager parts and it was the default option.
OSEL supply it because it was identified as a safety requirement and a solution was engineered into the ALVBOV to incorporate it.
Personally from experience I feel there might also be a slight comfort improvement over the Drager option but its minor, subjective and just related to ergonomics. You bailout off both the same way by tucking them under you chin.
The origin for Drager having a gag-strap is the same as EVERY currently sold military rebreather, be it Drager, Aqua-Lung, Divex, OSEL, OMG, Cobham or Carleton. The military operators simply require it for safety, as the French military study demonstrates. If not fitted with a gag-strap and half mask, the diver will be wearing a FFM and now most likely with dual mode OC/CC.
Making comparisons to old, obsolete equipment isn't a great selling point. Compare it to a Golem Shrimp or Divesoft BOV, both of which are by far the most popular aftermarket BOV's.
Both are about as equally tested as the Divematics BOV! However a good comparison of both
a new BOV at the neighborhood – The Rebreathing Space
Golem Shrimp
OC WOB doesn’t meet EN250 IIRC so is >3.0J/L at 50m Air 62.5lpm. At least triple that of ALVBOV.
CC WOB is published only for 40RMV, but extrapolated to 75lpm 40m Air is ~1.44J/L. Quite a bit over twice that of ALVBOV. Or on its own the same as OSELs entire CCR….
Divesoft BOV
OC WOB meets EN250, so we know its at least better than 3.0J/L. But no better than that, or else they would claim it….
CC WOB is unknown. Liberty eCCR WOB is however relatively high and there is likely a correlation.
Hollis BOV
OC WOB doesn’t meet EN250 IIRC so is >3.0J/L at 50m Air 62.5lpm. At least triple that of ALVBOV.
CC WOB is unknown. But we know it adds 0.3J/L over the Hollis DSV, so can’t be great.
rEvo BOV
OC WOB reportedly meets CE to 40m, so we know its at least better than 3.0J/L at 50m. But no better than that, or else they would claim it…. Have we seen any mention of CE certification for the Horizon, yet?
CC WOB is unknown. But reported by rEvo as being slightly better that rEvo DSV.
OSEL ALVBOV
OC WOB 0.89 J/L at 50m Air 62.5lpm
http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf
CC WOB 0.57 J/L at 40m Air 75lpm
https://www.opensafety.eu/datasheets/ALVBOV_40m_75lpm_air_081014.pdf
CE certified to 100m. Safe to dive on to 350.
Poseidon BOV
OC WOB reportedly same as Poseidon 2nd stage but undocumented.
OC WOB is unknown.
ISC BOV
OC WOB doesn’t meet EN250 IIRC so is >3.0J/L at 50m Air 62.5lpm. At least triple that of ALVBOV.
CC WOB is unknown.
APValves BOV
OC WOB meets EN250, so we know its at least better than 3.0J/L. But no better than that, or else they would claim it….
CC WOB is unknown. Inspiration/Evolution WOB is however high at the limits of EN14143 and there is likely a correlation.
