co2 hits? bov or not

[Brad_Horn]

Do you not see a market of the Osel ALV BOV for us rebreather divers who have loop direction flow from left to right?
If your figures are right, what i assume, i and sure many others would be interested
If i look at the GG shrimp, it goes like hot cake.
Is it really about the production ( engineering) cost not to offer left to right or is there some other reasoning (logic) behind?

Elmi, there is simply not the real demand. At the moment rec/tec divers are only at the initial evolutionary stage of knowing that a BOV is a good thing to have.
As you can tell by divers not knowing what the actual WOB is in OC and CC modes for the various BOVs they buy and that most of them fail or simply do not have CE.
Heck most divers still have no idea what the WOB of their rebreather is.... let alone an individual component.
If anyone disagrees with me, just tell me the WOB in CC and OC modes of the second best performing BOV that you can buy?

It will only be once the industry matures to a point where divers start seriously demanding WOB testing for their BOVs and only buying the best. That it might be worth OSEL offering a left to right flow ALVBOV. If a rebreather manufacturer, company or individual wants to submit to discuss a PO for an OEM run of left to right ALVBOVs, just email sales@opensafety.eu to discuss. There will be a significant MOQ!
The ALVBOV has the lowest available WOB and is the only BOV available that is CE certified for use to 100m in both OC and CC modes.

If there is not the obvious demand, which there is not as evidenced by the "GG shrimp selling like hot cake", it is pointless OSEL spending the quite considerable cash on retooling the ALVBOV for left to right flow and having it re certified to EN14143 and EN250 by SGS. It is a non-core business to OSEL as they will never sell a left to right flow rebreather.
Now for those that have left to right flow rebreathers already and are interested or for those manufacturers offering these rebreathers who want to lower their units WOB and offer a safer BOV or enable the unit to be more easily CE certified, there is a different perspective.

Brad, whats the difference in WOB when using a Helium-based gas with something like 30%+ in it when considering your OC regulators.

I am sure that Simon mitigates his lack of knowledge of the WOB for the OC aspect of the BOV by using a less-dense gas (trimix) than required for the CE which means the WB will be automatically less...

Agreed. Of course the use of high He mixes drops your WOB, BUT the ratio of the difference remains unchanged.
Is it safer breathing off a lower WOB loop/reg/BOV option? I think the answer will always be of course, but we do not yet know where the dividing line is! Or if when you bailout, what is safer. At the moment when Simon bails off his loop, he probably guesses he is going to a similar WOB using his OCB from the loop and then if he goes to an OC reg, it is 1/3 the WOB (assuming equal He content across the 3 gases).

I am not aware of any published WOB testing having been done on any regulators/BOVs with 30%He mixes. I am sure a clever engineer could probably work it out from the maths knowing the published WOB testing from in Air at 40m/50m and 10/90He at 100m though.

I'd like to know why actually, I snipped off the rest of you post because it goes off on a bit of a tangent. Does not seem like a simple fact to me that L to R and R to L would be fundamentally different.

Simple engineering design and then verification by formal unmanned testing to get the lowest WOB to offer ALARP to divers.

It 'could' have been made to be left to right, but this is the opposite flow direction to what commercial and military rebreathers use. and there just isn't the demand for it.

sorry Brad you lost me. can you explain what gas flow direction has got to do with WOB?

A company has spent the money on R&D to supply BOV in Right to Left flow that has low WOB in both CC and OC modes.

The direction itself is irrelevant, other than you either don't know what the WOB is for most left to right BOVs or it really just isn't all that good.

Nonsense! All else being equal, there is no difference in WOB going from L/R or R/L. To say otherwise is just marketing spin!

Randy logically correct. But for the Shrimp, please correct me if I am wrong; there is no unmanned testing published confirming this?

The difference is in what other BOVs are available in the two flow directions and their comparative WOB performance. Until a manufacturer steps up to the plate and makes a better L-R flow BOV with much lower WOB, at the moment the best BOV WOB performance both OC and CC is available only in a R-L configuration.

maybe the kind of problems that only happen to divers with a BOV.

What kind of problems only happen to divers with a BOV?

 

[rjack]

What kind of problems only happen to divers with a BOV?

Perhaps not only to BOV using divers, but plumbing in a hypoxic mix and bailing to it shallow or at the surface seems to be a significant concern.

 

[Randy Thornton]

Randy logically correct. But for the Shrimp, please correct me if I am wrong; there is no unmanned testing published confirming this?

Brad, your original comment was that the WOB on a R-L configuration was somehow inherently superior. This is obviously false. I did not address the issue of comparing existing BOVs on the marketplace, nor do I care to do so. There are way too many other considerations in addition to WOB, including ergonomics, availability, size, ease of use, reliability of company, etc. etc.

 

[lizardland]

You can test this yourself. Just assemble your unit without a scrubber, set it at 0.21 ppO2. Then go for a walk (a reasonable proxy for light swimming) with a nose clip on. Have a friend along make sure you don't hurt yourself.

In my limited experience with O2, the respiratory drive goes sky high and the anxiety matches it. Which leads to massive perceptual narrowing. Is that "narcosis" in the same sense as other gases? I don't know, but on a practical level its debilitating - as most victims of a CO2 hit here are validating.

I've done similar tests although sitting down. I remember thinking that all I needed to do was spit the mouthpiece and breathe. I struggled doing that, I had to force myself. That was sat on a couch. Co2 scares me. Nitrogen never did.

 

[Mark Chase]

Are you not the one who despises automation because it makes you complacent? Isn't there a risk that the BOV, unconsciously does the same to a diver, and will stop him from worrying to much about overexertion or a failed stereo check?

The OP was maybe hoping that everyone would tell him: go for a BOV, this will save you in all situations, even though it is an additional pain in the rear to handle underwater and maintain above water.
I just wanted to point out that some very experienced divers (which I am not) do not think so, and they probably have good reasons for their choice. I suspect that they are investing in more pre-emptive action, checks and cross-checks, and would all the same be grateful if an exhaustive list of all cases of hypercapnia fully analyzed by their victims were available to all to learn from.
Statements of the kind "s***t happens to the best" are self-defeating. It also will happen with BOV (if of a different kind) and maybe the kind of problems that only happen to divers with a BOV.

You rais some good points there


Yes I am antiautomation where it removes the diver from any possabuility of decision makeing. However I must admit, I didn't consider a BOV to be automation except versions that switch to OC because the computer told them too.


You say that proper preporation and proper planning can minimise the risks and I 100% agree but for me proper contingancy planning includes minimising the bailout related risk by haveing a BOV I hope to never need.


ATB

Mark

 

[Brad_Horn]

Brad, your original comment was that the WOB on a R-L configuration was somehow inherently superior. This is obviously false.

Randy, That is not what I said.
Ask yourself which loop flow direction has a BOV available with the lower WOB, L-R or R-L? It is simple 'fact' that it is R-L.

Why R-L for loop flow comes down to a myriad of other design considerations and usability requirements.

The best low 'known' WOB L-R BOV is the JJ-BOV which at 1.06J/L at 40m at 75lpm on air in CC mode is nearly twice that of the ALVBOV at 0.57J/L
In OC modes, as the JJ one failed CE based on WOB, the difference is even greater.
There might be less of a comparative difference with either the Poseidon or Hollis BOVs, but until they publish testing, users are in the dark.

I did not address the issue of comparing existing BOVs on the marketplace, nor do I care to do so. There are way too many other considerations in addition to WOB, including ergonomics, availability, size, ease of use, reliability of company, etc. etc.

Agreed.
But to the diver needing the BOV in emergency, the difference in having that lower WOB 'may' be critical to the divers survival. How much 'may', even the experts cannot tell us. Whereas some of the factors you have listed may only be nice to haves and in any event, are not mutually exclusive.

Unfortunately for buyers of BOVs a lot of the listed nice to haves are subjective. The same happened with open circuit regulators twenty years back where when simple directly comparative WOB testing at ANSTI was introduced into reviews. See this one from 1996 for example http://www.divernetxtra.com/gear/regul696.htm Where the WOB testing was extra evidence supporting previously only subjective reviews over what regs were good and which were not. For good reason this rapidly changed those regs preferred for more serious diving.

I am sure the rebreather market will eventually catch up, but until that time you cannot get a truly low WOB L-R BOV. For those that accept mediocre WOB performance in a BOV as good enough, cool.

 

[jas kev]

You've hit the nail on the head, from reading a few post regards those who have had hits I wondered if the chance of a co2 hit could be all but eliminated through build diligence and not pushing the scrubber. At the moment I feel I will add a BOV though I would plumb into deep bailout and not dil. Quite often I will get three dives from a dil fill and can see no point going onto a half full 3lt

You rais some good points there


Yes I am antiautomation where it removes the diver from any possabuility of decision makeing. However I must admit, I didn't consider a BOV to be automation except versions that switch to OC because the computer told them too.


You say that proper preporation and proper planning can minimise the risks and I 100% agree but for me proper contingancy planning includes minimising the bailout related risk by haveing a BOV I hope to never need.


ATB

Mark

 

[MeRodent]

At the moment when Simon bails off his loop, he probably guesses he is going to a similar WOB using his OCB from the loop and then if he goes to an OC reg, it is 1/3 the WOB (assuming equal He content across the 3 gases).

I'm guessing that when Simon bails off his loop he's not thinking about what the WOB is or whether he brought his PDF's along for the dive so he can check... He's more than likely thinking "can I breath off this?" and how to end his dive.

At the end of the day, WOB is one of a number of factors that are part of the decision process that are assessed before making a choice. Only you and a few others go on and on about it being the only choice.

 

[Mark Chase]

I'm guessing that when Simon bails off his loop he's not thinking about what the WOB is or whether he brought his PDF's along for the dive so he can check... He's more than likely thinking "can I breath off this?" and how to end his dive.

At the end of the day, WOB is one of a number of factors that are part of the decision process that are assessed before making a choice. Only you and a few others go on and on about it being the only choice.

Exactly

Whern I tested the Paragon reg at depth (KISS BOV) I knew I wouldent be able to breath it at depth in an emergancy. JJ breathing was a bit naff but the wet initial breath was a big problem. Golum MK1 was a struggle to heavy breath on CCR mode but good as OC

Now with the shrimp I never feel lung tierd post dive, and as an OC reg its good enough at any depth. I am sure it could be better but it feels like it would suffice


I dived TX 40s and 50s OC and still have them on my bailouts. I considered them to be an excelent breath. My mate had S Pro R190s and I borrowed his rig once and couldent beleive that any one would tolerate such a high cracking resistance on a OC reg.

I only mention this to demonstrate that my personal tolerance for poor performing regs is quite low.

ATB

Mark

 

[Stan]

Golem Shrimp has an average WOB of 0.4077J/l (according to the blurb on the Golem site).

Was on a PDF too - so it must be right.....

 

[Brad_Horn]

I'm guessing that when Simon bails off his loop he's not thinking about what the WOB is He's more than likely thinking "can I breath off this?" and how to end his dive.

I am guessing you are of the school that does not believe in planning the dive before doing it. On the dive why would you have to think what your WOB is?
I am guessing that Simon has done his bailout planning based on his equipment selection. Not knowing his WOB in order to plan this, may just mean his bailout sequence is not quite as optimum as it could be, if the lowest WOB is truly needed.

At the end of the day, WOB is one of a number of factors that are part of the decision process that are assessed before making a choice. Only you and a few others go on and on about it being the only choice.

Agreed
but it is one of the few things that you can use as a non-subjective selection criteria.

Now with the shrimp I never feel lung tired post dive, and as an OC reg its good enough at any depth. I am sure it could be better but it feels like it would suffice

and Mark, until you and others expect and require better performing BOVs. For the L-R crowd, that is probably about as good as you will ever get as an option.

As far as your comment of "for an OC reg its good enough at any depth". Until we see studies determining the deciding line between good enough and not. On how low the WOB is actually required to be for safely bailing out.
I can only agree with you, whilst privately thinking that groupthink attitude is probably going to catch somebody out at some point.

Golem Shrimp has an average WOB of 0.4077J/l (according to the blurb on the Golem site). Was on a PDF too - so it must be right.....

That is right. But the devil is in the detail as that WOB test was done at 40lpm. Which is the much lower flow rate used for scrubber testing for CE. It it a nice bit of marketing spin that conveniently for GG muddies that waters.
CC WOB is typically tested and results published for 75lpm at 40m on Air
OC WOB is typically tested and results published for 62.5lpm at 50m on Air

Coincidently that average Shrimp WOB data of 0.4077J/L at 40lpm at 40m on Air coincides with the WOB of the entire rebreather I dive. Which is 1.44J/L at 75lpm!

 

[Dave1w]

Have been playing around here in Bali and did a very hard (fast for me), long swim on bailout relatively shallow, with an Apeks ATX40, I did pop back onto the shrimp halfway through. Worth giving it a try and see how you get on.


Sent from my iPhone using Tapatalk

 

[jas kev]

Thanks for all the replies, having read the thread all the way through I feel a BOV is the way forward. A shrimp has been ordered. Now to decide how to rig it, current thoughts are plumbed straight into deep bailout. Possibly a reg also on bailout to hand off.

 

[Mike Ferguson]

good plan. a second stage to hand off on deep bailout isn't a nice to have, it could save someones life.

 

[Mark Chase]

good plan. a second stage to hand off on deep bailout isn't a nice to have, it could save someones life.

And on a selfish note, a caustic coctail may render your BOV useless

OC regs on all my bailouts and a 2m hose on the deep one for cave dives.

ATB

Mark

 

[colinicky]

good plan. a second stage to hand off on deep bailout isn't a nice to have, it could save someones life.

F*** off ! My gas is mine, all mine you hear :ignore:

 

[mick4707]

F*** off ! My gas is mine, all mine you hear :ignore:

Deep bailout can be sold at a premium at depth :haha:

 

[Ben Field]

and Mark, until you and others expect and require better performing BOVs. For the L-R crowd, that is probably about as good as you will ever get as an option.

"If you build it they will come"

Expectation and Requirement aside if there is no product to buy we have to make do with what is available- should it be up to the customer base to tell manufacturers what to make?

I realise turning a highly developed R-L BOV into a L-R one isn't as simple as many might assume but surely with the lion's share of the market being L-R its a win-win situation to offer one? More people buying your BOV might bring a few connected sales of the whole units?

 

[Brad_Horn]

And on a selfish note, a caustic coctail may render your BOV useless

Mark, there is a way to mitigate this risk....

"If you build it they will come"

Ben, there is a complete rebreather for that, inclusive of BOV....

Expectation and Requirement aside if there is no product to buy we have to make do with what is available- should it be up to the customer base to tell manufacturers what to make?

Agreed. But at the moment some are still hard pressed identifying they need a BOV.....
BOVs have been around for a long time, and recognised by those in the know as a mandatory requirement for safety for nearly as long.

If the diver doesn't know or care to know the WOB of their BOV to begin with, how many really want a lower WOB one?
and I know divers don't care to know, cause not a single one (unless they are diving with an ALVBOV) can tell me the OC and CC WOB, of their BOV.

Taking this a step further. As understanding that BOVs are actually quite different in performance, is something that rebreather manufacturers on this thread have indicated they don't want to know about and as subject matter experts on the effects of CO2 on rebreather divers do not yet factor it into their diving, is there really a true demand for a high performance L-R BOV?

If I was dropping $10k+ on a new Rb that doesn't meet ALARP for a BOV amongst other criteria, I would have a few questions of that manufacturer, so yes, I would say customers should be telling manufacturers what they expect. BUT that is balanced by the upfront open disclosure of the manufacturer in publishing their FMECA and design verification testing reports, identifying why the rebreathers were designed that way to begin with. If there is a valid reason for a manufacturer doing something a particular way, what is the customer base actually asking?

I realise turning a highly developed R-L BOV into a L-R one isn't as simple as many might assume but surely with the lion's share of the market being L-R its a win-win situation to offer one? More people buying your BOV might bring a few connected sales of the whole units?

Ben, Not if there is not sufficient commercial return to justify the very significant expense in doing so.

In an ideal world I can see a perfectly valid business plan for a L-R manufacturer who wants to offer his customers a lower unit WOB (by quite some margin) with an integrated BOV that has the OC WOB of a good reg, or a third party supplier who can see the long term business success of supplying the ALVBOV in L-R config; however, any such project is snookered as long as folk accept as optimum the fitting of BOVs with unknown performance to their loops, that cause unknown performance changes to their unit (higher WOB, lower scrubber duration, risk etc).
Your immediately competing with non-CE certified BOVs, with 2, 3 or 4 times the probable WOB, that have minuscule R&D, testing and certification costs (if any), in a market where even the subject matter experts on the affects, have no idea nor interest in the issue. That is not to say that Simon et al are not interested but it is understandable that they are gaffer taped from discussing the issue. As testing L-R BOVs for WOB to identify where they stand and then doing the R&D to lower the WOB sufficiently for them to be competitive, is very expensive. A catch 22, especially when you can currently sell them without R&D, testing and certification costs.

Until folk cotton on to the fact that OSEL/DL have spent significantly more on R&D than the USN's Mk15 program, which is how they have achieved the highest performing CE certified BOV amongst a few other things, I can see the status quo remaining quite unchanged. As a result of that R&D program, there is a reason why certain things are the way they are, despite being quite different perhaps, to what customers would either ask for or think they want! As such it is pointless OSEL offering a BOV that is the opposite to the right flow direction and something that intrinsically can not work with any of their rebreathers.

However, a bit of a win win for the rEvo crowd at this point in time, or at least it will be when they start to crop up with CE certified ALVBOVs on their units. They can get rid of their OE ADV and get rid of an unnecessary lp hose+manifold, lower their units WOB by an unknown amount, fit better wider bore breathing hoses that do not need hose weights and almost certainly increase their scrubber duration when measured at the mouth - all in one hit.

 

[uwxplorer]

However, a bit of a win win for the rEvo crowd at this point in time, or at least it will be when they start to crop up with CE certified ALVBOVs on their units. They can get rid of their OE ADV and get rid of an unnecessary lp hose+manifold, lower their units WOB by an unknown amount, fit better wider bore breathing hoses that do not need hose weights and almost certainly increase their scrubber duration when measured at the mouth - all in one hit.

@Brad_Horn: I'd be willing to beta-test a ALVBOV on my rEvo or at least would be interested to hear about such a test and detailed report about it. The problem I see is that OSEL doesn't for a start answer requests for info. I have asked about their mushroom valves in the past (using their online information request form) and never received an answer. I bought the new rEvo valves in the meantime.

Just to clarify the reason why I am not currently using a BOV, which I suppose is the reason why a lot of rEvo users don't: when trained on a unit, you are instructed (if not ordered) to no modify your unit for the first 50 hrs while you get used to diving it. I am well past 100 hrs on my unit, and still feel like I have to learn a lot about its quirks, and adding an unsanctioned bit of kit is not something I want to do without serious thinking, especially since my diving is currently not putting me in situations where I expect to run into issues of overbreathing my unit for instance (I take my scooter in all my "deeper" dives in any case).
Once I reach a stage where my diving becomes more challenging (deeper, essentially) and I expect WOB to increase substantially, I will start looking into this seriously again. And not just in terms of BOV versus DSV, but indeed in terms of WOB.

I was initially obsessed by the lack of BOV like a lot of new rEvo users I suppose and I unlearned this obsession by surviving each and every dive I have performed since without one. This doesn't prevent me from reading stories about CO2 hits very carefully, but as I pointed out earlier, not to reinforce my former obsession, but instead, to understand the root cause of those hits and what can be done to prevent them.

BTW, what's missing in most of these theoretical discussions on WOB is that it depends a lot on the diving conditions. A machine test is fine, but you can always put yourself in a real diving situation where you are well past the testing parameters of your unit and even the best unit will come short and make you run out of breath, CCR or OC. Part of getting to know your unit and becoming a good diver is to learn where its "flight envelope" resides. If you try to loop the loop on a Cessna, you might not live to tell the tale. Same on a rebreather.

In summary, it is perfectly fine to dive a rebreather without a BOV, as long as you stay within certain diving parameters.