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.If you are diving solo doubles, then you always take a bailout bottle as a truly independent source of gas.
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.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?
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.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.
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 this instance you still have to come off of the loop for decompression.
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.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.
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
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.
- 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.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.
A HUGE issue with doing this is if the free flow is due to a defective first stage and you do not have another second stage or an OPV on the first stage, you have just created a bomb that will go off in a few seconds after you shut the valve. Then you are forced to turn the valve off with a hose lashing around your head spewing air in an uncontrollable manner......hopefully not beating the crap out of you in the mean time. At least with a second stage free flowing, it's easy to control and if necessary breath from, not so with a blown hose. Never, ever put a hard isolation on a first stage, otherwise something will give violently.SurfLung wrote:What About Shut-Off Valves?
- Rich just brought to my attention that we can buy shut-off valves to turn off a free flow right at the 2nd stage mouthpiece of a single hose regulator. It strikes me that not being able to reach the valve knobs on the tanks behind your head makes the isolation a useless pre-caution. Having a shutoff right at your mouthpiece would serve you better.
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