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New rEvo BOV

Discussion in 'Rebreather Diving' started by stuartv, Oct 2, 2019.

  1. silent running

    silent running Manta Ray

    # of Dives: 1,000 - 2,499
    Location: Brooklyn, N.Y. U.S.A.
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    I’m not selling anything and I’m not making an argument, I’m giving my opinion. And I don’t care how old something is when discussing design differences and physics. There is nothing particularly innovative in the current group of BOVs, unless you are referring to the Shrimp/Golem BOV orienting the OC diaphragm at an angle in it’s second version, just like the old NATO pod. Apparently, everything old is new again at some point..;-)

    As for service, I was pointing out that plenty of people bought those CCR heads knowing they must send them back at considerably more expense than would be for a much smaller pc like a BOV. And basic self servicing of the ALVBOV (OC 2nd stage and flapper replacement) is an option, any self servicing of a Poseidon or Liberty head is not.

    What’s popular is of little concern to me, I care about performance and ergonomics.

    The Shrimp and IBOV are good BOVs, but both use Draeger flappers and have higher WOB than the ALVBOV. Flapper valves are a major factor in WOB, and speaking of “old” designs I don’t think Draeger has redesigned their flappers in decades. I also like that the mechanism for switching the ALVBOV to OC is spring loaded, makes switching a one finger effort and negative tests easier than turning the lever on a DSV...
     
  2. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
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    Here's some of (only?) definitive work documenting the value of gag straps (aka mouthpiece retaining strap)

    https://www.researchgate.net/public...mong_French_Military_Divers_From_1979_to_2009

    Revos supply the Drager strap as a default (although somehow some instructors remove them or have their students remove them in MOD1). AP makes a similar strap as an option.

    I have used one on my Meg for 5 years now, and talked about it here and on other forums. I don't think any of my buddies have used them.
     
  3. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
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    Do you offboard the dil to inc volume due to higher consumption if profile is saw tooth Rjack? I am guessing as this is BO too you have a cut off pressure for refill.
     
  4. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
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    I offboard the dil because for cave diving I use the same mix as I would on OC and for BO. So for 0-100ft cave diving I use 32% dil typically. It cuts down on O2 consumption and stabilizes your buoyancy to not have the solenoid firing whenever the adv fires - if you have air dil they are constantly chasing each other. And bailing to air is going to be a huge hit on your deco.

    I can also end up using a lot of dil on sawtooths - but that volume isn't so much dil its more for the wing. LP85s of 32% is about 14lbs of gas or 7L of wing/suit gas (when using nitrox BO). That's a fairly hefty volume to correct on sawtoothy profiles. I'm neutral with empty BOs and a semi-puffed up drysuit (not vacuum packed). You'd be surprised how many cave divers aren't neutral with empty BOs.
     
    Jack Hammer and JonG1 like this.
  5. Dsix36

    Dsix36 Solo Diver

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    You might even be surprised at how many people have no clue of their buoyancy with empty tanks.
     
    rjack321, OceanEyes and kensuf like this.
  6. uwxplorer

    uwxplorer Rebreather Pilot

    # of Dives: 500 - 999
    Location: Los Angeles
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    Looking again at the pictures provided in the thread, and comparing them with those available on Mares' Horizon pages, the two BOVs appear very similar (aside from some branding difference on the face plate). Which begs the question of the design specs of the BOV.
    If designed for the Horizon, max depth 40 m, essentially no or very little deco, direct trip back to the surface type of bailout, you can't expect the same performance as for a unit designed for tek diving. And the injection moulded design fits the bill of a cheap(er) product for the masses (remember, this is part of the Horizon which is sold for about half the price of a rEvo, AFAIU).
    Which is why I am at the same time eager to hear more reports on its actual behavior under water, and worried that it could be a source of avoidable screw ups. The Facebook group pointed at by the OP comprises an alarming proportion of divers plugging it straight into their dil cylinders, with apparently not the slightest afterthought (or guidance from the manufacturer for that matter).
    This group choice is interesting as the Horizon doesn't have a back mounted cylinder, therefore the bailout has to be plugged into a slung stage (and therefore is provided with a quick disconnect hose, from what I can gather).
     
  7. Tassi Devil Diver

    Tassi Devil Diver Barracuda

    # of Dives: 1,000 - 2,499
    Location: Tasmania, Australia
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    The Shrimp BOV on my rEvo is plumbed into both on board and off board, with the priority being for on board with higher IP.
     
  8. JohnnyC

    JohnnyC Divemaster

    # of Dives: 1,000 - 2,499
    Location: United States
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    I'm assuming you have redundant inflation on both wing and drysuit from offboard bailout?
     
  9. Tassi Devil Diver

    Tassi Devil Diver Barracuda

    # of Dives: 1,000 - 2,499
    Location: Tasmania, Australia
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    ^ Sure do separate 1.5l bottles for wing and suit.
     
  10. Brad_Horn

    Brad_Horn Nassau Grouper

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    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, 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.

    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.

    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.

    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.
     

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