Isolation manifolds & modern DH extended range diving

[luis]

Ok, I will try to share what I have found out, but I will share a bit of background first. I will try to be clear when it is just my opinion, versus when it is information that can be verified or a known fact.

I have found that there is actually more than one opinion camp when it comes to isolation manifold, independent doubles, and related redundancy/ risk management approach.

There is the DIR philosophy, and there are many other philosophies. TDI as a training agency is much more open minded and I have talk about different configurations using my double hose with some of their instructors, when their central office was here in Maine.

I actually did some technical diving classes about 10 years ago with a double hose and the Sherwood manifold ( with independent regulators). The instructor had no issues with my setup and he actually liked it. An interesting side note, the instructor actually cut me about a 50% discount since he felt that he also learned a lot during the class. I was doing some extended range diving long before those classes.

Note: the Sherwood manifold is classified as an isolation manifold by some since it does isolate both regulators, but some groups do not consider it an isolation manifold since it does not split the gas from the two cylinders.

There are also other manifolds (some modern and some vintage) that can also be configured with two independent closing/ isolating regulator outlets, but that do not contain the central isolating valve. Therefore, for this discussion I will refer to the “modern isolation manifold” as the one that contains the central valve intended to isolate the two cylinders.

In contrast I will call my preferred manifold as the Sherwood two outlet manifold.

Some pros and Cons.

The Sherwood vintage manifold will isolate and be able to close either regulator if one is malfunctioning. Closing the valve to the malfunctioning regulator (free-flowing or leaking) will preserve your gas supply to be accessed with the other regulator.

Regulator malfunction (free-flow or leak) is the only common form of malfunction where gas will be lost.

The manifold is simple with minimal number of O-rings and connections.

The Pros of the modern isolation manifold:
The Modern isolation manifold does the same function as the vintage Sherwood manifold, but it adds the potential of isolating the cylinders (which in theory will preserve half of you gas).

There are only four types of additional gas leak malfunctions that the modern isolation manifold is capable of mitigating.
1. A burst disc release underwater
2. A tank neck O-ring failure underwater
3. A manifold joint release underwater
4. A high velocity projectile puncture of a cylinder (like from a bullet)while underwater

Let’s look at the probability and how many cases have been documented of any of the four modes of failure. All four are theoretically possible, but some have never happen and (IMO) all can be avoided with minimal care.

Of the four, number 4 is the only one that I have seen, but only in the movies. I have not heard or seen any documented cases of this type of failure actually happening.

Number 3, I have heard of one documented case when someone dropped a set of double and it only started leaking after they got in the water. The explanation for the incident is that most of the damage was done during the drop, but it was not visible at first. The thermal shock after entering the water was the last straw the caused the manifold joint to leak.

Number 2, I have not seen or heard any documented cases of this type of failure with a substantial leak underwater. I have seen many rental AL 80 in the Caribbean with minor leaks around the neck, but nothing catastrophic and they are always visible from the beginning of a dive.

Number 1, I have read of only two incidents, but I have only kind of confirmed one case. There may be more , but both cases that I read about seem similar enough that they might have been the same or not. In any case it was a burst disc letting go shortly after entering the water. To me, the basic explanation for this is thermal shock on a burst disc that has not been service or was at the very edge of its stress level (probably an over fill).

Note: These are the only confirmed incidents that I have read about (or somewhat confirmed). If anyone knows of other confirmed incidents, please share them. A description of the incident would be helpful or a link would be even better.

IMHO, the first three modes of failure can be totally avoided with proper equipment service and care against damage. Again, this is my opinion and it is only based on observations during several decades of servicing dive gear and my technical background, but no actual study.

In a cave or wreck environment I can see the potential for an impact to the manifold, but it would require a fairly severe impact to cause a catastrophic damage. The Sherwood manifold is actually much less susceptible to impact due to the type of metal to metal joints that it uses (no O-rings).

Thermal shock is the only other extra load that can affect a burst disc or a manifold, but this type of stress will always happen at the moment of immersion.
The issue is are we adding extra isolation and complexity for an unrealistic risk? That is the question.

The Cons of the modern isolation manifold.
1. It adds mechanical complexity with a few more points of failure and bit more delicate manifold (IMO, this is a relatively minor issue)
2. It adds procedural complexity were the diver has to decide what to close first in the case of a failure.

I have not trained on this type of manifold so I am only going to write about incidents that I have read.

Item 1, seems like a minor issue, but I have inspected this type of manifold and some do seem to be somewhat more delicate, but nothing that I would be concerned.

Item 2 is where I have read more of the controversy about this manifolds. I have read of several incidents (but I don’t have direct confirmation) where the diver wasted a lot of air/gas fumbling with the isolation center valve first, before closing the outlet to a leaking regulator.

As I recall the worst case issues was when the leaking regulator was behind the divers head and he could not easily identify the leak source.

I recall reading and hearing of several similar incidents incident were an unnecessary amount of gas was lost due to fumbling with the wrong valve.

It seems that good procedures and training will mitigate this fumbling issue, but I find it troubling that I have heard or read of it from several sources. Again, no firsthand experience.

The manifold is not easy to reach and the question that needs to be answer is: does that extra valve that needs to be reached really add any reasonable protection.


On my readings I have also found others that will only accept independent doubles, no manifold, but that seems to be a smaller group of divers.

I have also recently read of some that believe the safest kit is a very large single cylinder with two outlets (Y or H valve).

Now the modern side mount has brought back the concept of independent doubles with the major advantage of easy reach of the valves.

As I mentioned, very little here is my opinion, a lot of it comes from different schools of thought that I have been reading about. I am not going to defend or argue about someone else’s opinion or point of view. The incidents that I have read about are also from many different sources and covers years so I am going by memory.

Risk management is all about calculating the amount of risk versus the consequences. A risk management table is easy to read, the hard thing is figuring out the probability of the risk and figuring out what are the real interim consequences (not just the potential final).

BTW, the mix-mount configuration I have been playing with does have a few extra (minor) points of failure, but it does add one more independent redundancy easily isolated gas supply.

[antique diver]

Good analysis, Luis. For years we pondered the question of the safest valve or manifold configuration for cave diving (or other dives where there is no direct "escape to the surface".

My thoughts are that the modern isolation manifold is pretty simple to deal with and pretty safe for diving with a buddy or team. To address the question about the isolation valve being hard to reach and operate, the cylinders should be worn high enough for the user to reach the valve with either hand, possibly even by using the other hand to push up the doubles up and tilted a little toward the hand reaching for the valve. Maybe that valve doesn't have to be opened all the way, making shutting it off faster to accomplish.... lot of differences of opinions here too. Basically it's a pretty safe config when diving with others that you can trust your life with.

Diving alone in overhead environment is a whole different story. Having a fair number of occasions to dive alone in those conditions, I settled on independent cylinders when back mounted for a couple of reasons. The first was that I had two air supplies that were totally independent of each other, so had less risk of losing all the air in the event of a manifold failure or some event that prevented me from quick isolation. The other reason was that my air management techniques would be virtually identical when wearing back mounts as when using side mount. So I began to dive independent whether I was with a team or by myself, so that in an emergency I didn't have to decide how to deal with the air management... it is always the same whether back mount or side. One less thing to figure out when things go wrong.

I know there are arguments against independents, but I feel most comfortable that way in overhead. Glad to dive with normal manifolds for most recreational open water dives, as I like extreme simplicity for those dives. I am always willing to listen and learn from the great collection of knowledge here, so I welcome and even request your comments, suggestions, and yes, even your harassment!

[luis]

My thoughts are that the modern isolation manifold is pretty simple to deal with and pretty safe for diving with a buddy or team. To address the question about the isolation valve being hard to reach and operate, the cylinders should be worn high enough for the user to reach the valve with either hand, possibly even by using the other hand to push up the doubles up and tilted a little toward the hand reaching for the valve. Maybe that valve doesn't have to be opened all the way, making shutting it off faster to accomplish.... lot of differences of opinions here too. Basically it's a pretty safe config when diving with others that you can trust your life with.

I haven’t read anything saying that the modern isolation manifold is particularly unsafe or anything like that. What I have read (and I tend to agree with it), does it really gain you any real extra safety? Or does it fall more in category of protection against extreme (close to unrealistic) events?

Yes events like a blown burst disc can and do happen (I have seen many, but never underwater). But the specific events that it protects against can all be mitigated before you get to the water’s edge.

Again I have read a lot of different point of views. I totally believe that there is not such a thing as one size fits all, but when analyzing the risk and consequences I personally like to use the most realistic information that I have on hand. But it is up to every individual to make their own decisions.


I should add, that I personally never liked wearing the cylinders so high that the back of my head can touch them. That is in part a personal reason why I am not a fan of the valves on the top. If I was going to use an isolation manifold, I would come up with a way of wearing the tanks with the manifold on the bottom (like Cousteau used to do it).

It wouldn’t be that hard to do some similar pluming as in the RAID unit with the manifold on the bottom and a piped regulator outlet on the top for a DH, but I don’t want to travel with cylinders.



I like the selection of independent doubles for your application.

It is kind of interesting that for a while there used to be a lot of arguments against independent doubles, but now-a-days I don’t see anyone bringing up the same arguments against side mount. Side mount is basically the same as independent doubles.

The arguments that I remember were mostly based on the gas management procedures, which I never understood what was the big issue. It is just interesting how perception has changed.

[luis]

My thoughts are that the modern isolation manifold is pretty simple to deal with and pretty safe for diving with a buddy or team. To address the question about the isolation valve being hard to reach and operate, the cylinders should be worn high enough for the user to reach the valve with either hand, possibly even by using the other hand to push up the doubles up and tilted a little toward the hand reaching for the valve. Maybe that valve doesn't have to be opened all the way, making shutting it off faster to accomplish.... lot of differences of opinions here too. Basically it's a pretty safe config when diving with others that you can trust your life with.

IMO, if there was a real need for a quick acting valve, someone would have already be offering a manifold with a quick acting isolation valve.

High pressure, 1/4 turn, high reliability, precision valves are commonly available in industrial application. The valve in the manifold is a relatively small valve. It would not be a big deal to design it with a 1/4 turn motion.

Even the reserve bypass valve on my 1957 Dragger twin tank manifold had a 1/4 turn actuation and it was accomplished with a very high pitch threaded globe valve.

I just don't think there has been a true need for it... but the existing configuration sure sells a lot of classes and training opportunities.

[tbone1004]

being a cave diver who doesn't fit into the norms, I should be able to lend something to this.

Isolation manifolds- I have them, but only use them for the convenience of being able to not switch regulators. I only really use them in open water. Added redundancy is important for me when teaching so I don't have to call a dive in the event of a failure, and don't have to switch tanks at all over the two days of open water dives. I also dive it in the ocean but simply out of convenience of not having to change tanks between dives.

Indy doubles- I use these for a couple reasons. If for whatever reason I need/want to dive backmount in an overhead environment, then I prefer independent doubles in order to have true independence of my gas supply. Feathering a valve is annoying as hell and you never want to do it, you do what you have to do to get out. Is having access to all of it more convenient? Definitely, but I'd still rather dive indies. The other and arguably larger reason why I have indy doubles is so I don't have to drain them when the tanks go in and out of sidemount configuration which is my primary configuration for cave diving. I really don't like diving backmount in caves.


Thoughts about double hose technical diving. I think the double hose needs to be treated like a rebreather. There, I said it. It obviously isn't, but because you can't really have multiple double hoses on your back due to the inconveniences of multiple loops, and they can't really be tied together, it has to be treated like a rebreather. So what does this mean for me? It means that if I'm diving in a technical environment, I'm going to carry the gas that I need in a single cylinder or set of doubles with a non-isolation manifold on my back with my Kraken as the only regulator. I will then carry some sort of bailout to get me out from where I am. In OW, that may be nothing, but an AL40 is perfectly sufficient for just about everything to get up to deco bottles and basically disappears.

In a cave it can become a bit more problematic and would likely end up as some sort of clunky triples setup. A LP121 cave filled gets you about the same amount of gas as double 72's, and putting a set of cave filled LP50's or something on the side of that *basically like a ccr setup* gives you 165cf of gas for planned diving, and about the same in the 50's for bailout purposes. A set of cave filled 104's gives you about 180cf for total penetration, so it's about the same as diving a set of 104's.
A bit more conservative than thirds with the 50's, about right with 46's, but it's workable. I probably won't ever get something like that set up since it would be heavy, expensive since I don't have the tank brackets, and a bit cumbersome, but it would work no differently than a bmccr

For me right now, I'll probably take it deep on a single 121 with an al40 as bailout since it will be in OW

[Bryan]

Once this information is made into a general consensus or current best practices it should be made into a sticky and also a PDF available for download. We can put it over on SB but I'm afraid at this time we might be burnt at the stake. (ask me if I care )

[Ron]

First of all, let me just say that I'm very happy that we are having this discussion. I've been an advocate of tech double hose, or whatever we want to call it, for years. I also appreciate the approach to this, where we are having at least a semi-academic discussion of this.

The International Journal of Aquatic Research and Education, 2009, volume 3, pages 162-177, documents cave diving fatalities from 1969 to 2007. You can read it here:

http://research-repository.uwa.edu.au/e ... xport.html

Here is a snip from that scholarly paper:

snip.JPG

If we use the overall column, which includes trained, untrained, and unknown status divers, we see that of all cave diving fatalities from 1969-2007, only 7 out of 211 are related to equipment failure, which is 3%.

I'd like to preface that I can find no scholarly research where a tank valve o-ring or burst disc has ever failed underwater. This report does not list the nature of the equipment failure, but in over 50 years of cave specific diving, only 7 gear failures of any kind have been documented. I want to mention that because we are talking about incredibly small chances of failure, or at least within my risk appetite 3% is small. I'm probably exposing myself to more risk with the Americium in my smoke detectors in my house than I am with my equipment in technical diving. It is also worth noting that this paper is cave diving only.

Now, having said that, what would happen if a burst disc blew underwater and you didn't have a manifold that could be isolated? Good question right?

http://www.advanceddivermagazine.com/ar ... conds.html

Advanced diver magazine tested this. An 80 cubic foot tank will completely drain from 3000 PSI in roughly 74 seconds. I would posit that we could use rough math to say that double 80s would drain in 74 seconds x 2 or 148 second, which is 2 minutes and 28 seconds. That's not a lot of time if you are at 200 feet.

There's my main point. I feel like a burst disc failure is rare, but likely would cause you to run out of gas without the ability to mitigate that risk. Not having the ability to mitigate that risk violates a number of technical diving rules of the road, or at least as I was trained. It violates the rule of redundancy. It violates the principle of self-sufficiency in that I was trained to be able to bail out of any technical dive on your own without assistance.

This is all about assessing risk, and I totally agree with that. I am personally not willing to accept the risk that I would kill someone else, or myself, if I had a burst disc or tank valve o-ring fail. The single loss expectancy is my life, so I'm not willing to accept a 3% annualized rate of occurence.

There's the rub for me. IF I could isolate my back mounted doubles with a double hose, then I would use a doublehose to do any of the technical diving that I already do. IF I could find an alternate solution that was elegant (in the engineering sense of the word) and simple, then I would be willing to use that instead.

What I will not do, personally, is cobble a bunch of random adapters together to force my doublehose to work for tech, when back mounted doubles with 2 single hose regulators work far, far better currently. There are numerous engineering case studies of solutions to non existent problems that result in unanticipated consequences and systemic failure. For electronics, I would suggest Sega's Sega CD as an example:

"Former Sega of America senior producer Scot Bayless attributes the unsuccessful market to a lack of direction from Sega with the add-on. According to Bayless, "It was a fundamental paradigm shift with almost no thought given to consequences. I honestly don't think anyone at Sega asked the most important question: 'Why?' There's a rule I developed during my time as an engineer in the military aviation business: never fall in love with your tech. I think that's where the Mega-CD went off the rails. The whole company fell in love with the idea without ever really asking how it would affect the games you made."

(the emphasis in bold was mine)

https://en.wikipedia.org/wiki/Sega_CD

I just don't want to be one of those people doing something with no real engineering reason because I happen to like the technology. We need to make it an equivalent tool for the job of backmounted doubles with 2 single hose regulators. That's when people will use it. These last 4-5 paragraphs were my personal opinion only. We also need to keep in mind that the number of doublehose tech divers is probably about 8 right now assuming that the people on this board are representative of the overall ratio of double hose tech divers to regular double hose divers. I am, at my core, a soldier. Soldiers like simple, reliable, and repeatable.

Simple, reliable, and repeatable is the whole reason I dive vintage gear. I think, and this is my opinion, that every vintage equipment diver I've ever met has said the same thing in one way or another.

This goes without saying, but just so someone doesn't come behind me and say I didn't notice this, people can and should do whatever they like. It's your life, and it's your funeral. I am speaking from the perspective of advancing the overall sport of vintage equipment diving. I get that there are people who do all kinds of things with DIY gear. There are still guys I know who are so cheap that they use sandpaper to resurface regulator seats when Bryan sells them for 15 bucks, and they know that if Bryan stops selling parts we are all equally screwed. People don't often operate rationally, and that has some solid science behind it. Here's a link for that too:

http://uxmyths.com/post/2607991907/myth ... e-rational


In summation:

We need a simple, reliable, repeatable way to dive isolated doubles with a doublehose regulator mounted in the center of a person's back, like conventional isolated manifolded doubles. Also, I would dive indy doubles for backmount, but since I already have 2 sets of isolator manifold doubles, I just don't. If I knew of a way to dive a double hose and a single hose with indy doubles, I would consider that as well. I'd also dive side mount, but I don't currently. I have nothing against sidemount. Again, if there is a simple solution to dive a doublehose sidemount, then I would consider that too. I'm not married to isolator manifolded doubles. I would not use a complex setup like the one Luis uses. I will not dive long deco profiles with manifolded doubles that cannot be isolated. Those are my opinions.

[tbone1004]

so the question to ron is why we actually use manifolded doubles that can be isolated, and why we need to use an isolator, etc.

Isolated manifolded doubles:
Allows access to full gas supply needed with either regulator in normal use and with one
Allows you to shut off one regulator in the event of regulator failure

If you are concerned with the burst discs, plug them

We need doubles for gas volume, and the ability to have a redundant source of gas supply in the event of equipment failure. What the study is not going to dictate is how many incidents went unreported for whatever reason.

Now. Let's go back to how we think about the double hose and how we approach technical diving and why, especially looking at the UTD sidemount, and BSAC training schemes. With UTD sidemount manifold, they are trying to force backmount doubles paradigms into sidemount instead of treating it as a different system. With BSAC, they don't allow primary donate on any of their courses because it is incompatible with CCR diving. Is this fair, or should it be treated as a different equipment setup with different paradigms?


As mentioned above, I think in a technical setting the double hose needs to be treated like a rebreather. With the addition of the DSV to the product lineup, as well as the prominence of CCR's in especially cave diving, it's actually a great option to start seriously talking about.

Let's look at a standard bmccr, Meg, HH, etc. It is an 8" OD "tank" with two support bottles on the side. You can't realistically donate the loop, so there is no primary donate option. The unit is basically a backmount single with a pair of pony bottles on the side, one of which may be used for bailout in an OW environment, and the other is O2. Offboard bailout can usually be plumbed into the system via various quick connect type systems.

Downsides to using a double hose as an OC rebreather compared to an actual CCR for technical diving use. The main downfall is the limited accessibility to alternate gases for switching. So you set up the DH for your bottom gas, but then all of your deco is on a single hose. Only way to really fix that is if there was a hookah port and you could easily switch off of the backgas *read not shutting the tank valve off. I don't know how you could do that without IP trickery which is what I think Luis did for his mix mount. Not something I want to deal with.

So to Luis, Bryan, and Herman. Is there a way to relatively easily give the Kraken an alternate IP input line where you can switch the first stage off without turning off the valve to be able to pull from some "offboard" source?

[Ron]

I'm going to borrow some of your words:

"so the question to ron is why we actually use manifolded doubles that can be isolated, and why we need to use an isolator, etc.

Isolated manifolded doubles:
Allows access to full gas supply needed with either regulator in normal use and with one
Allows you to shut off one regulator in the event of regulator failure"

We also use manifolded doubles to prevent a total gas loss in the event of a o-ring or burst disc loss. I know you were sort of saying that, but I want to be explicit. We use manifolded, isolated doubles to do this:

-Access to full gas supply needed with either regulator in normal use.
-Access to full gas supply needed with one regulator shut down.
-Access to half of the remaining gas supply in the event of a tank failure.

I think we probably both agree on that.

I do not plug burst discs. To do so is to invite liability, as I use conventional dive shops to fill my tanks. As a professional, I do not want to invite the liability that comes with violating reasonable man theory. Everything that I do in diving that impacts others I do from the perspective of reasonable man theory:

https://www.personaldefensenetwork.com/ ... -doctrine/

You can do whatever you'd like, but speaking from the perspective of advocating for the sport, I don't generally encourage people to expose themselves to extra risk and liability, especially since risk is my actual day job.

"We need doubles for gas volume, and the ability to have a redundant source of gas supply in the event of equipment failure. What the study is not going to dictate is how many incidents went unreported for whatever reason."

Your second sentence is anecdotal. The absence of evidence is not the evidence of absence.

https://en.wikipedia.org/wiki/Argument_from_ignorance

"Now. Let's go back to how we think about the double hose and how we approach technical diving and why, especially looking at the UTD sidemount, and BSAC training schemes. With UTD sidemount manifold, they are trying to force backmount doubles paradigms into sidemount instead of treating it as a different system. With BSAC, they don't allow primary donate on any of their courses because it is incompatible with CCR diving. Is this fair, or should it be treated as a different equipment setup with different paradigms?"

I don't reach BSAC, or UTD, and I don't care what they do. I do not have a dog in this fight. I don't teach sidemount. I'm not a person you need to sway in any of these regards.

"Downsides to using a double hose as an OC rebreather compared to an actual CCR for technical diving use. The main downfall is the limited accessibility to alternate gases for switching. So you set up the DH for your bottom gas, but then all of your deco is on a single hose. Only way to really fix that is if there was a hookah port and you could easily switch off of the backgas *read not shutting the tank valve off. I don't know how you could do that without IP trickery which is what I think Luis did for his mix mount. Not something I want to deal with."

I agree. I'm not going to do a bunch of janky stuff to my gear just to dive a doublehose. For me to use a doublehose for tech, it needs to be a simple, reliable, repeatable solution. We agree on this totally.

"Is there a way to relatively easily give the Kraken an alternate IP input line where you can switch the first stage off without turning off the valve to be able to pull from some "offboard" source?"

This, to me, is added complexity. I like to phrase things like this simply.

You conduct the driver's exam for you county. One day, a person shows up with a 1985 Dodge Aries K car. The person behind him in line shows up with 2 motorcycles welded together. The person with the motorcycles argues that it is a car, so he should be allowed to take the driver's test in it. Should he be able to?

Now, you are a technical diving instructor. Someone shows up with standard tec gear ala PADI Tec, Naui NTEC, GUE, etc. Someone else shows up with a doublehose, and 3 tanks all rigged together with various manifolds and high pressure hoses. How do those two guys learn to dive together? How do you teach them to? How do they standardize even if they don't learn to dive from an instructor? Do you see where I'm going with this?

When I took my deco class in 2010, I took it with a retired friend of mine from SOCOM. Great dude. He let me do half of it in DIR style backmounted doubles, and the other half in double 80s with a solid bar manifold, a horsecollar, a doublehose, etc just like the military used to do. He let me do that because that's how decompression diving was done in the military, which he knew about, and because it followed some sort of standard. If I went deco diving with another guy who used vintage gear with single outlet doubles, a horsecollar, and a doublehose, then we could build procedures for emergencies that were standard, and practice them. We did dives in a doublehose to 150 feet with 10-20 minute decos. It was a great time. We also did some of the old school safety stuff and hung a cylinder at 15 feet, and since we were diving gradient factors of 50/70 low/high, it brought us up shallow right away for our decos.

That's my point. If we end up doing something that gets sold, then it needs to be more than a bunch of hoses that you hook together. It needs a foundation upon which you can build procedures and train people effectively on them. I'm sure we agree on this too, because you have probably been tech diving longer than I have, because I've only been doing it for 10 years. I'm approaching this collaboratively, in that I'm sure we can all probably agree on a common set of stuff as far as gear maybe someday and then we could all test dive it. We could even possibly meet somewhere and do the trimix dives as a team even.

BTW, one late addition to this rant. I've used a larger single tank with a bail out slung before, just like you mentioned that. Maybe there is some common ground there. We could use a HP 120 with a doublehose and the VDH plate, then sling a bailout bottle conventionally like with regular tech diving. That's a pretty good idea on your part.

I cut a profile for 150 feet for 10 minutes on Ideco, with 50/70 gradient factors. It lists 60 cubic feet for back gas, so a 120 would be plenty of reserve gas. If you brought an al 40 slung, then you would easily have enough deco gas for both people to use on the way up. That's a pretty solid idea on your part. More technical profiles would get tougher to do that way, but we both already know that.

[tbone1004]

my argument against burst discs is that they aren't actually to protect anyone during filling as proven by their lack of use in Europe. The history of burst discs is to prevent cylinders from exploding in a fire. The other is that the burst discs for the HP tanks in particular, but even AL80's are set at pressures around the compressors max pressure of 4500-5000 psi. I don't know of any commercial shops with 6000psi compressors in this country. Based on those arguments combined with the safety factors for burst pressures of cylinders, I figure there is no real risk of leaving them plugged.

My second sentence was not anecdotal. Your citation was from cave diving fatalities, it does not include incidences of equipment failure in general, only those that resulted in a fatality where that fatality could be contributed to equipment error. I have personally had a first stage basically explode under water, in a cave. That obviously is not included in that study but is an incidence of completely losing access to the gas in that bottle unless I chose to bare tank breathe. Feathering was not an option. That is a known data point that would have resulted in a mandatory shutdown of one post on a set of doubles that did not result in a fatality. The study assuming it factors in all deaths over a period of time gives us a percentage of what caused those fatalities but isn't really useful for decision making. How do you factor in those types of incidents that didn't result in a fatality? Just because I didn't die doesn't mean I wouldn't have if I did not react appropriately or if I had an equipment configuration that did not allow me access to sufficient gas to get out.


I do see where you are going, but that is no different than one showing up in sidemount and one in backmount. One with standard Hogarthian rigging vs a secondary take setup a la BSAC. One in OC vs. one in CCR. One in CCR with a bov vs one in CCR without a BOV. Instructor has to adapt if they are going to allow different configurations but that is exactly my point. You shouldn't/arguably can't force this into the normal hogarthian paradigm or you are going to horribly compromise the system, a la UTD sidemonut manifold.

So, to bring back to your single manifold type setup on the double hose, the argument against that is you get the double hose for the bottom mix, but can't use it for your deco. Since deco will often exceed the bottom time, and you can't swap tanks on your back, then you have to come off of the loop for deco which defeats the purpose of having the DH in the first place, hence treating it like a CCR where you can plug in multiple gases.
Just got off the phone with Herman about this.

So. Here's how to do this. We're gonna use Piranha since Randy is Bryan's neighbor
Put a regulator hose on the Kraken.
Stick this on the end of the reg hose
http://www.piranhadivemfg.com/item/Adap ... -male-2947
then one of these guys on the end of that
http://www.piranhadivemfg.com/item/BOV- ... g-QD--2399
Stick the other side on the end of a regulator hose from an offboard bottle. He unfortunately doesn't have just the female side for multiple bottles which is annoying since I prefer the female side on the offboard bottles.

QD is important because you don't want O2 hooked up at 100ft, bad news bears.
Voi la, now you can hook up whatever offboard gas you want, the other 2 LP ports will function to give you inflation gas, life is good.

BUT, Herman raised a good point. Especially for those of you that dive lots of salty stuff. A VERY little bit of water gets shoved in every time you connect those QD's in the water which is really not great. If you use Swagelock QC4's it is the equivalent of a couple drops for every connect. For the salty stuff, that's a lot. In cave diving it's all nice clean fresh water and typically not going into anything important. For this, it's going directly into the first stage low pressure chamber, and that's a lot less than ideal.

So for me it's back to the drawing board on how to get this to go and if it can realistically go forward. At this point, I'd be OK diving with a DH for all bottom work with an independent bailout bottle or Sherwood style manifold and just accept that I have to go off the loop for deco.

[luis]

So. Here's how to do this. We're gonna use Piranha since Randy is Bryan's neighbor
Put a regulator hose on the Kraken.
Stick this on the end of the reg hose
http://www.piranhadivemfg.com/item/Adap ... -male-2947
then one of these guys on the end of that
http://www.piranhadivemfg.com/item/BOV- ... g-QD--2399
Stick the other side on the end of a regulator hose from an offboard bottle. He unfortunately doesn't have just the female side for multiple bottles which is annoying since I prefer the female side on the offboard bottles.

QD is important because you don't want O2 hooked up at 100ft, bad news bears.
Voi la, now you can hook up whatever offboard gas you want, the other 2 LP ports will function to give you inflation gas, life is good.

BUT, Herman raised a good point. Especially for those of you that dive lots of salty stuff. A VERY little bit of water gets shoved in every time you connect those QD's in the water which is really not great. If you use Swagelock QC4's it is the equivalent of a couple drops for every connect. For the salty stuff, that's a lot. In cave diving it's all nice clean fresh water and typically not going into anything important. For this, it's going directly into the first stage low pressure chamber, and that's a lot less than ideal.

You basically described my hookups in my mix-mount setup, which are simple LP connections to the DH second stage.
BTW, I have also address the salt water intrusion by partially opening an inline valve to dry flush the connection during the connecting process.

I also have full control of which cylinder is supplying the gas. The valve cylinders are all normally open. I have inline shot off in my two side cylinders and a full pneumatic lock on the back gas first stage. The control system is not uncommon in pneumatic control systems. The first stage in the DH is closed so it cannot be back-fed.



Ron,
There are many alternatives.

I would like to quote Akimbo from ScubaBoard:

Life (and safety) is all about choosing the compromises that suck the least.

In this thread:
https://www.scubaboard.com/community/th ... nt.545511/

[Ron]

Ron,
There are many alternatives.

I would like to quote Akimbo from ScubaBoard:
Life (and safety) is all about choosing the compromises that suck the least.

Luis,

I agree. If we could put our heads together, and wave a magic wand, then our theoretical end product would meet all our functional requirements. Then again, most engineering endeavors are not that way because of the limitations of the thing itself. An AK-47 can be cleaned with dirty motor oil, but it isn't a terribly accurate rifle at 500 meters. An M4 needs fancy first world graphite lubricants to run without jamming, but it shoots to 550 meters. I think you, Tbone, and I all agree that we are working with what we have.

So for me it's back to the drawing board on how to get this to go and if it can realistically go forward. At this point, I'd be OK diving with a DH for all bottom work with an independent bailout bottle or Sherwood style manifold and just accept that I have to go off the loop for deco.

Tbone,

I'm in your boat. For now, I'm doing the doublehose as my backgas, with my redundancy being a slung cylinder with a single hose. I do welcome trying other stuff if we come up with it. I would also welcome a fancy new manifold that let us run a center outlet regulator like a doublehose, with a side post single hose for redundancy and some sort of isolation mechanism. To my knowledge, such a thing does not currently exist, but if we came across something that would work, I would put my name in the hat to give it a shot.

Really, the only things you lose with the old Sherwood manifold with the center outlet are the ability to isolate gas in the event of a catastrophic gas loss. The one I had still had two valves in order to shut off the center post or the side post. That's a tough risk to accept knowing if a burst disc or a tank valve o-ring go that I have under 3 minutes to sort it before I would either get horribly bent or drown while I was sitting at 200 feet. To your original point, you are almost better off running 1 large single tank at that point, because either way you have to bring a bail out to not break some pretty key tenets of modern technical diving.

I'm going to marinate on this for a while. We are smart. I'm sure we can come up with something.

[Ron]

Humor me please:

What about this:

https://www.golemgear.com/p-323-lola-un ... valve.aspx

With something like this?

http://www.wmd.com.tw/products/item/266

Again humor me. You can isolate either tank from the other, and run a doublehose. Obviously we would have to make sure that we got the spacing right and that the center to center spacing of whatever doubles you used would work. This is actually more redundant that a conventional isolator manifold, albeit mechanically more complex. This is a start though. You guys have been doing this a lot longer than me...let's spitball about this. You can even shut the tanks off, disconnect the middle part of the manifold, and make them singles with no loss of gas. Also, you can then reconnect them with this crossover cable and dive them as backmounted doubles for two single hose regulators:

http://www.lola.cz/en/eshop/speleo-tech ... hpi-l--300

If we could make this work you could literally use the same 2 tanks for single tank diving, double hose single tank diving, single hose isolated doubles, and double hose isolated doubles. Say that three times fast. This would be a system. One set of doubles that did it all. We'd probably have to make a doublehose backplate for doubles because the DIN fitting would make the regulator stick out further which we could mitigate by adding bends to the plate like a conventional backplate for diving doubles...but with a doublehose cut out or something. Luis, to your original point, this would mean that valves would be easier to reach, because the shutdown valves are not behind your head.

They even make plugs for when the other ports are not in use, which have pressure releases built into them:

https://www.youtube.com/watch?v=qG9jVOv ... e=youtu.be

Also, Lola is a Czech company and they also have a vintage equipment museum on their page:

http://www.lola.cz/cs/muzeum/scuba-vintage-museum

If this isn't providential I don't know what is...either that or I'm drunk. Either are possible. Personally, I would need to see the schematics or drawings to make sure that this all works how I think it does.

[luis]

That would work just fine for what you are trying to accomplish. I would be curious about the cost of the components, but functionally it would do what you are trying to do.

I have a couple of sets of vintage European double (Poseidon and Dragger) that are assembled in the same way, two independent cylinders with DIN outlets (previously known as the European threaded connection) and a few DIN manifolds the take the two cylinders and provides one center outlet.

This vintage kits do not have a second outlet once they were joined, but they use the same approach for connecting the cylinders.


But, my requirements are very different. I am not going to travel with my own cylinders. I want to rent a couple of AL 80 (or three) with whatever gas I need to use and set them up on the spot. That is why my mix-mount solution is (IMO) the best solution for my purpose. My new setup also provides independent triples if needed.



On the subject of “a burst disc or a tank valve o-ring let go”, I personally fill the this concerns are somewhat overrated. When I do what I consider a realistic evaluation on the probability of failure, I personally feel that this kind of failures fall in a similar category as being hit by a meteorite. Again, that is my assessment based on "mode of failure" analysis and I am very willing to accept that level of risk. That is my personal assessment and I don't expect anyone else to follow it. Note: I don’t carry meteorite insurance either.

In my assessment, I am assuming a well maintained and properly installed neck O-ring. If the tank neck/ valve joint has no flaws (confirmed by good inspection), there is a metal to metal contact with zero gap to extrude the O-ring.

A burst disc failure underwater can also be mitigated with good maintenance and proper installation. It can also be taken further, but I totally respect using an appropriate burst disc. It does protect in the case of a house fire and we build our houses out of wood around here.

I can expand on this subject, but I don't think it is necessary. I understand it is hard to assess the probability of a failure, but I am comfortable with my own personal assessment.

I realize that when using a risk assessment table, if the consequences are high, some will not accept anything less than a zero percent probability of failure.
Again, each individual needs to make their own decision as to what level of risk you are willing to take, based on the information you have and trust.

[Ron]

Yeah, I agree. It's not like we have to dive the same way. Really, as long as shops will rent you tanks or let you use a dive boat knowing the kind of setup that you plan on using, I suppose it doesn't matter.

I'm thinking more along the lines of how VDH could market and sell something that the average technical diver would use. From my perspective, this setup looks professional, would work on a dive boat, and would probably pass cursory scrutiny from a dive boat operator. That's all anecdotal.

Also, If this doubles setup works, then you could have divers use the same standard for gear as basically every other tech diver with the exception of side mount, which is nice as well.