Isolation manifolds & modern DH extended range diving

Questions about using a BCD, Backplate or other modern gear with your double hose? This is the place for answers.

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tbone1004
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Re: Isolation manifolds & modern DH extended range diving

Tue Jul 11, 2017 2:40 pm

the lola valves are certainly an option, just a bloody expensive one.
the question becomes whether you need isolation and why. If you are diving solo doubles, then you always take a bailout bottle as a truly independent source of gas. The argument becomes whether you really need to have the doubles for anything other than volume. Is the isolation manifold something that you really and truly need and does it justify the complexity and hassle to incorporate something that we do just fine without in sidemount?
The lola valves are fairly popular in a small segment of the rebreather market, but their cost makes it quite annoying. Valves are $120 each, crossover is $80, and unsure what the WMD bit is, but likely at least $100. Makes it prohibitive. Functional, but prohibitive. Again though, what does it gain vs. a large single unless you really need that backgas capacity? What it doesn't address is how to use the double hose for different gases. In this instance you still have to come off of the loop for decompression.

In terms of how we go about this. It is a point of contention between the DIR community, and those of us that try to think for ourselves. The DIR configuration is phenomenal for what it was designed for. LONG cave penetrations in Florida. It doesn't work as well in different cave environments, open water, or where configuration adaptations are required. The actual WKPP guys will adapt when they have to, but will default back to the DIR config and a lot of the people who talk about it, don't really understand it. I.e. those that refuse to put tank boots on doubles when diving off of a boat because of a realistically nonexistent entanglement hazard vs. damaging the boat itself.

I think Luis has the adaptability portion ironed out with mix mount. Strap on a single AL80 to mount the double hose and secure it, then be able to plumb in offboard cylinders. The concerns here are the acceptance of the pneumatic lock for decompression gases without shutting the valve off to the main tank. That to me is the real key to make this work.

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Ron
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Re: Isolation manifolds & modern DH extended range diving

Tue Jul 11, 2017 4:18 pm

If you are diving solo doubles, then you always take a bailout bottle as a truly independent source of gas.


I do not carry a bailout ever when solo diving on isolated manifolded doubles. I don't see any point in doing so. There is virtually no risk from my perspective with diving 2 first stages, 2 second stages, and an isolator manifold. That's 2 tanks, and 2 regs. That meets every agency I train with. Every instructor I've ever had has also done that. GUE also does that. Are you from outside of the states maybe? I've never seen a guy here do that actually.

Is the isolation manifold something that you really and truly need and does it justify the complexity and hassle to incorporate something that we do just fine without in sidemount?


Sidemount is equally annoying in different ways. I've seen people get their butts handed to them trying to dive sidemount from a boat. I've seen people fall like old people trying to beach dive sidemount. Sidemount is awesome for caves and lakes. I don't dive sidemount, because I live in Puget Sound and all my diving is done in the sound. I have to do long walks, sketchy entries, etc. I would pay you money to try to do some of the entries I do here in side mount. Again, just my opinion.

Again though, what does it gain vs. a large single unless you really need that backgas capacity? What it doesn't address is how to use the double hose for different gases. In this instance you still have to come off of the loop for decompression.


A single tank is a single point of failure. A single dip tube means that a single clog negates all your gas. I personally know of at least 2 people who have rented crappy scuba tanks and had corrosion or rust clog the dip tube or foul the first stage regulator. I don't want those kind of problems at 200 feet. That is just me. For me, it's 2 tanks, 2 first stages, and 2 second stages with very deep dives and long decos.

In this instance you still have to come off of the loop for decompression.


You always come off your primary regulator for deco, unless you deco on backgas. Every single diver already does that. For me, that's a non-issue.

In terms of how we go about this. It is a point of contention between the DIR community, and those of us that try to think for ourselves.


I don't have a dog in that fight. I'm a PADI instructor with training from PADI, NAUI, and TDI. I have boots on all my doubles, because not being able to stand your doubles up is stupid, and also because I don't dive caves. I do run my regulators the DIR way, but that's because to me it makes the most sense. The parts of any agency that I use are the ones that make the most sense. I run my deco bottles only on the left, because I think running a long hose on the same side as a deco bottle (if you run them on the right) is stupid and makes no sense. I just want you to know where I'm at on that. I don't even have any certs from GUE, and I don't ultimately care, even a little bit, about what they do. There's only one shop who does mix up here anyway, so the idea that I'm going to recreationally dive 30/30 is insane. I'd rather buy another Rolex than dive mix for a year. So I'm not a Kool-Aid drinker, just in case you were curious. Every thing that I do in my diving I do because I feel like it is simple, reliable, and repeatable. I don't do over-engineered, and I don't do things just because other people are doing them. That's just me.

As I've stated earlier, for smaller decos, a set of single outlet doubles, like old double 72s, and a single double hose are fine. You can bail out on your deco gas presumably, and then do the ascent and deco on deco gas. For a more complicated dive, you cannot bring enough bailout gas or you would have to sling 1 80 and 2 40s with the 80 for bail out and the 2 40s for deco. Either way, it becomes complicated. Luis' setup is also complicated. I feel like the setup I mentioned with the Lola valves is the most elegant solution, and the most in line with conventional diving. I get that none of us are going to agree with that. I would like to see a video of Luis diving that setup on a rolling dive boat. Again, maybe I'm wrong and it is super easy to do in a drysuit in seven footers. I'm wrong a lot, just ask my wife.

I'm probably not going to take all my doubles apart and go to all this trouble myself, so I'm probably going to continue to do longer decos on backmounted doubles and not use a doublehose for long deco dives at all. I would gather that we are probably not going to build consensus on this, which is fine.
The impossible missions are the only ones which succeed. -JYC

tbone1004
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Re: Isolation manifolds & modern DH extended range diving

Tue Jul 11, 2017 4:50 pm

Ron, the big thing here is you have to stop thinking about this from a single hose DIR style mindset and start thinking about this more like a CCR type system.

Yes, on single hose regs *except the UTD system* we come off of our primary regs for deco, however that largely negates the point of diving a double hose in the first place since deco is quite often longer than the bottom portion of the dive. In a single large tank, you have an independent bottle for "bailout" no different than you would in a CCR system. The key is really to not think about this as an alternate setup for a twin tank OC setup, but to think of it as a CCR style setup where the goal is to stay on the loop for the entire dive and have offboard bailout since a single catastrophic failure removes that entire component of the system.

There are VERY few dives are a single AL40 would be insufficient bailout with an AL40 for O2 as proven by the CCR guys. In a cave it would be cumbersome and probably not practical, but for open water other than entry purposes, there really is no advantage to doubles vs a big single with a bailout/pony bottle as it is no different than what is done with a CCR. You are still trying to cram the double hose peg into the single hose hole. They are different shapes, treat them as such and think outside of the box instead of trying to cram this into it when it will never fit

kworkman
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Re: Isolation manifolds & modern DH extended range diving

Wed Jul 12, 2017 4:55 am

Most of this stuff is over my head but it is a good read at 4:48am instead of doing my job. I have no intentions of doing cave or open water technical diving but interesting stuff. I wanted to get into vintage style diving because of the simplicity and tried the whole DIR style set up with a single tank and hated it. I always ask about the old time divers who did long deep dives with doubles and single outlet manifolds and never had any issues. Isn't this what the Navy does? I thought I had more to say but my eyes are starting to roll to the back of my head and I still have 2 hours to go before quitting time.

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Ron
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Re: Isolation manifolds & modern DH extended range diving

Wed Jul 12, 2017 12:38 pm

tbone1004 wrote:Ron, the big thing here is you have to stop thinking about this from a single hose DIR style mindset and start thinking about this more like a CCR type system.

Yes, on single hose regs *except the UTD system* we come off of our primary regs for deco, however that largely negates the point of diving a double hose in the first place since deco is quite often longer than the bottom portion of the dive. In a single large tank, you have an independent bottle for "bailout" no different than you would in a CCR system. The key is really to not think about this as an alternate setup for a twin tank OC setup, but to think of it as a CCR style setup where the goal is to stay on the loop for the entire dive and have offboard bailout since a single catastrophic failure removes that entire component of the system.

There are VERY few dives are a single AL40 would be insufficient bailout with an AL40 for O2 as proven by the CCR guys. In a cave it would be cumbersome and probably not practical, but for open water other than entry purposes, there really is no advantage to doubles vs a big single with a bailout/pony bottle as it is no different than what is done with a CCR. You are still trying to cram the double hose peg into the single hose hole. They are different shapes, treat them as such and think outside of the box instead of trying to cram this into it when it will never fit



I don't care about using the doublehose exclusively. I just don't. I never learned to dive with only using one regulator for bottom gas and deco, and I don't dive a CCR nor want to learn how to use a CCR. I have zero desire to stay "on the loop" for the whole dive. There is absolutely zero functional engineering benefit to doing so.

I cannot possibly think of a reason to do this that has any merit with respect to functional requirements or data. I would argue that Luis' setup is for tech travel, which is a solid idea because finding backmounted doubles when you travel is a problem. I don't agree with his approach, but I don't have to because he's the one doing it. He has pretty solid ideas on why that work for him, and I support that. Now, having said that, if you want to stay "on the loop" because you think it's pretty, or neat, then do whatever you want. I don't do things in my diving without solidly backed up reasons though. I don't do things in mountaineering, firearms, or even watches without solidly backed up reasons.

If you can give me a solid reason, backed up with data, for why I should jury rig a bunch of extra tanks to my double hose, then I will gladly hear them. If your reason is "because I like it" or "because it is cool", or "because I dive a CCR", then I totally accept that for you...but not for me. For me a doublehose is a regulator...just like any other regulator. I have a Mistral, an Overpressure, a Kraken, a Stream Air, a NONMAG, a RAM, a Navy Type DA, and a Royal Mistral that I've rebuilt myself, so I feel relatively familiar with doublehose regulators. They are awesome, but they are no different for me from any other piece of dive gear I own. I'm not going to go to extraordinary lengths to force a doublehose to do something that I view as having no functional benefits from just using backmounted doubles with two single hoses. I don't like using a screwdriver as a hammer. Again, maybe I'm wrong.

I cannot possibly make this any clearer from my perspective, so just suffice it to say that I agree with your right to do whatever you choose, and my right to think that what you are doing doesn't make a lot of sense from my perspective. I take it on faith that you are an intelligent person, and that you have reasons for what you do. You should return the favor.
The impossible missions are the only ones which succeed. -JYC

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Ron
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Re: Isolation manifolds & modern DH extended range diving

Wed Jul 12, 2017 12:55 pm

kworkman wrote:Most of this stuff is over my head but it is a good read at 4:48am instead of doing my job. I have no intentions of doing cave or open water technical diving but interesting stuff. I wanted to get into vintage style diving because of the simplicity and tried the whole DIR style set up with a single tank and hated it. I always ask about the old time divers who did long deep dives with doubles and single outlet manifolds and never had any issues. Isn't this what the Navy does? I thought I had more to say but my eyes are starting to roll to the back of my head and I still have 2 hours to go before quitting time.



One thing I have learned from being mentored by a lot of divers with crazy amounts of experience, like Captain Tom here, Bryan, Rob, Greg, Roger, Bill, and others is that deep deco dives were done back in the day without a lot of redundancy. Typically, you and I would each strap on a set of doubles with a J-valve and a single regulator, dive deep, do deco on back gas, and then be done diving. The redundancy was in your buddy and maybe a hang bottle at 15 feet.

I have done deco dives this way. One thing to keep in mind is that unless you had access to fancy mixed gases and special tanks like the Cousteau team did, then your deco time was limited by the gas you could carry.

As an example, let's say we used double 72s and a Mistral to dive to a wreck at 150 feet of seawater for 20 minutes, using Buhlmann tables with gradient factors of 50/70 low/high which is a common set of factors supported by modern decompression research. I cut these tables using iDeco:

-150 feet for 20 minutes is 83.2 cubic feet of air.
-ascent to 120 feet is 3.5 ft3
-ascent to 90 feet is 2.8 ft3
-ascent to 60 feet is 2.1 ft3
-stop at 50 feet for 1 minute is 1.5 ft3
-stop at 40 feet for 3 minutes is 4.0 ft3
-stop at 30 feet for 4 minutes is is 4.6 ft3
-stop at 20 feet for 37 minutes is 35.7 ft3

This profile, if you and I dive it Keith, is 137.4 cubic feet of gas from splash to surface with a SAC rate of .75 CFM for dive and .6 CFM for deco. In this profile, neither one of us have any redundancy in our regulators other than buddy breathing, and no redundancy to prevent a total loss of gas from a tank valve o-ring extrusion, a burst disc failure underwater, and no positive way to manage our gas other than estimation if we chose a j-valve over an SPG. We have no gas in reserve, we are violating the rule of 1/3rds, and many of the tenets of " A Good Diver's Main Objective is to Live", which looks like this:

A Good Diver’s Main Objective Is To Live

□ Required volumes for all gases determined.
□ Required reserves for all gases determined.
□ Actual volume in all cylinders calculated and compared to required volumes.
□ All gases personally analyzed by diver immediately before dive.
□ All cylinders properly marked.
□ Gases compatible among team mates.
□ All valves and regulators tested.
□ Turn pressure(s) and gas matching (if required) determined.
□ Gas loss or failure contingency plans

Now, that's an extreme example. Many people, based upon books that I've read and people I've spoken to over the years, didn't do crazy deco dives with a double hose and double 72s. They did 150 feet for 10 minutes, with 9 minutes of deco at 15 feet. If they had a problem with their gear, then they buddy breathed for their 1 deco stop at 15 feet and then stopped diving. If they had a gear problem, then they buddy breathed to get to a hang bottle or their deco stop and buddy breathed at the deco stop.

Again, I think Luis was 100% correct when he said that ultimately the person is the arbiter of what his or her own appetite for risk is. In warm water, with a wetsuit on, I have done 10 minute decos with a single stop at 15 feet with just a doublehose and double 72s with a good buddy. I've actually done that with a few of the other VDH members here. What I personally would not do is a 150 deco dive with a single doublehose and double 72s in Puget Sound in a dry suit in 49 degree water where you cannot hang a bottle in a current. That I would do in backmounted isolated manifolded doubles with 2 first stages, 2 second stages, etc.

At the end of the day it's all about risk. You and I have been diving in just our shorts at Portage with a doublehose, a tank, no BC, and full foot fins. Super fun in Portage, but that would be super risky here. At the end of the day, it's all about stacking the deck in your favor to not drown or get bent, so you can drink beer and lie about how awesome your dives are over a steak.

Also, never be leery of participating in conversations like these. It's one of the ways you learn things.
The impossible missions are the only ones which succeed. -JYC

kworkman
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Re: Isolation manifolds & modern DH extended range diving

Wed Jul 12, 2017 9:25 pm

OK so let me try to get back on track to what this discussion is about. We are talking about using a double hose for extending range diving but also having the ability to have a completely redundant system through use of the modern isolation manifold should some mishap occur. I love the Sherwood valves that Luis uses and have 2 myself for my mini doubles which will give you 2 independent regulators should one fail but not isolate 1 of the tanks should one of them fail. In that case you are forced to carry a bail out bottle. I did this briefly when I dove a single tank. I was taking my deep diver course and I had both my first stages start free flowing at about 100 ft. Emptied my tank real quick. My instructor was on a rebreather and had a bailout bottle luckily so I had to use that until we got to the surface. After that, I slung a 40 to be safe.

Now independent doubles or the isolation manifold will give you 2 complete systems for redundancy. I used to think independent doubles was stupid but I really like the idea now because you can rent tanks from anywhere and have back mounted doubles and they are pretty much the same as manifolded doubles. The downside is you would have to switch regulators when one bottle is low where as the manifolded doubles you can stay on the same reg the whole dive so that's nice.

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Ron
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Re: Isolation manifolds & modern DH extended range diving

Mon Jul 17, 2017 11:58 am

Indy doubles become problematic with a doublehose. First, the doublehose is not in an ideal position. Second, switching from a doublehose to a singlehose that is co located in the neck area becomes clunky. Having a bailout is nice because it places the singlehose far away from the doublehose, and minimizes the chance that it all gets caught up.

Bailout bottles and a single tank are a fine solution, but there are many dive profiles that are out of the question in the setup. I feel like it sort of goes like this:

Single tank
Single tank with pony or bailout or stage
isolated manifolded doubles

At least that is how I do it.
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Re: Isolation manifolds & modern DH extended range diving

Thu Jul 20, 2017 2:39 pm

luis wrote: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.


- Thank you Luis. I am WAY under qualified to enter this discussion but I learned quite a bit from reading it. Your opening article sums up the topic and arguments for different systems a lot more clearly than I understood before. Everybody has to start somewhere and I my start was pretty amateurish: My buddy Rich was having trouble letting go of his modern BCD based diving methods to embrace vintage style double hose diving. We found a semi-vintage ScubaPro manifold that works like your Sherwood and I encouraged Rich to buy it. My argument was that he could use an original vintage double hose regulator off the center valve and just mount his entire modern single hose system on the side valve. He'd have everything he's used to diving with along with him.
- But once he got it all mounted on his tanks, I realized he looked a lot like a "Tech-Diver" and started calling his system an "Isolation" manifold. It didn't take long before the local PADI instructor told him "That's not an isolation manifold"... It seemed sort of like an insult. Its a heck of a nice piece of equipment he might be able to grow with and certainly nothing to deserve an insult.
- Your article and arguments for this type of manifold make good sense. I'm going to print it off and give it to Rich.
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