Isolation valves or full independent Doubles

[Nemrod]

My solo doubles rig is independent. N

 

[rjack321]

Re-breathers use this configuration, does not seem a big issue, why it is not so popular now days beside hose length issue. I don't see any real drawback of configuring my setup like this, only minor stuff but, I may missing something, this weekend it just will be practicing so I will not meet with my instructor, but I like your opinions as well, before I go more in deep detail about the kind of configuration I want with my instructor.

Because its actually quite complicated and not really necessary. And leaks are so far away from your ears that you won't be able to hear them and diagnose the problem. Most leaks on a manifold are regulator leaks and you can fairly easily tell which side its coming from and the magnitude even without a buddy. Although buddy's are good for confirming problems, they are also good for fixing entanglements and you can still get entangled with valve protectors etc down by your butt.

Not all CCR divers invert their tanks. Those that do, don't do it that way to reduce entanglements.

 

[Remy B.]

Not sure if you are asking me specifically or what the question is. Valve-down doubles is my preferred configuration and I am working a second generation protector similar to the one in the photo.



These are the only ones I could find on the market: VALVE PROTECTORS

I chose to make mine because I wanted more protection, reduced entanglement risk, and a more comfortable fit.

The question was in general, but for sure I appreciate your opinion, Akimbo about the protector on that picture, is that a independent doubles ?

---------- Post added November 13th, 2015 at 01:24 AM ----------

Because its actually quite complicated and not really necessary. And leaks are so far away from your ears that you won't be able to hear them and diagnose the problem. Most leaks on a manifold are regulator leaks and you can fairly easily tell which side its coming from and the magnitude even without a buddy. Although buddy's are good for confirming problems, they are also good for fixing entanglements and you can still get entangled with valve protectors etc down by your butt.

Not all CCR divers invert their tanks. Those that do, don't do it that way to reduce entanglements.

I guess one can do a crazy Ivan and see with your own eyes if you have a leak.

 

[decompression]

The picture with the protector is manifolded doubles.......gotta find a video of the valve drill for that.


Sent from my iPhone using Tapatalk

 

[Akimbo]

... Akimbo about the protector on that picture, is that a independent doubles ?...

My primary objective for building these rigs is for progressive equalization, which is explained in this post. The "equalization" part requires an isolation valve.

Progressive Equalization

The picture with the protector is manifolded doubles.......gotta find a video of the valve drill for that....

I don't have a video but it is really simple... which was my reason for building these rigs. Opening and closing the isolation valve is part of my dive plan and often occurs 3-4 times/dive, not a drill. There are lots of photos in the link above.

I designate the post valve on my right as I wear them (valve-down or up) to be my primary cylinder. The dive starts with both post valves open and the isolation closed. When the primary cylinder is breathed-down enough to notice breathing resistance, or some point before if I remember and can see an SPG, I reach back and open the isolation valve until I hear that the two cylinders have equalized. I then close the isolation valve again -- repeat as necessary.

The isolation valve is rotated on the manifold so it points directly at my butt. It is easy to reach by arcing my spine forward a little so the bottom of the rig pulls away from my butt a few inches. Anyone can do progressive equalization on a valve-up rig, but not nearly as comfortably or quickly, especially in a heavy drysuit.

As explained to me, progressive equalization was originally developed by the Royal Navy to provide a hard reserve before SPGs existed. They didn't have modern isolation manifolds but their doubles had individual cylinder valves that manifolded into a single regulator.

The technique continued to be used for working in black water when you can't see an SPG. It was later realized that these equalization events can be incorporated into your dive plan. For example, the first equalization can signal "leave bottom" on a deep dive or "time to turn back towards the boat" on a shallower dive.

 

[kwinter]

Keep in mind that trim will be enormously different if you invert your tanks. Rebreather divers struggle with being butt heavy because of this.


iPhone. iTypo. iApologize.

 

[PfcAJ]

Akimbo are you actually using that technique on technical dives with staged deco?

 

[Akimbo]

Keep in mind that trim will be enormously different if you invert your tanks. Rebreather divers struggle with being butt heavy because of this...

Trim for a rebreather diver is much more impacted by their breathing bags than if their baby cylinders are valve up or down. Often their CO2 canister is high on their rig, which is also very buoyant.

I haven't found trim to be much of a problem on these rigs, but I expect having to fool with weight and trim whenever I change almost anything. In my case, just wearing my weight belt a little higher did the trick. My next gen protector will be 60% lighter than these crude prototypes. One of the volunteers I work with at the Monterey Bay Veterans has a spectacular fabrication shop and will be building some for about six of us... if I can ever settle on a "final" design.

---------- Post added November 14th, 2015 at 10:06 AM ----------

Akimbo are you actually using that technique on technical dives with staged deco?

Of course, why wouldn't I? Normally I leave the isolation valve open once I reach a decompression stop out of laziness (especially on valve-up rigs), but it would be safer to continue equalizing.

Failure mode analysis favors leaving the isolation valve shut because you will not lose as much gas in the event of a sudden rapid leak, regardless of which side of the isolation valve the failure is on. Leaving it open means you will lose the gas on the "good side" of the isolation valve during the time it takes to analyze the failure and close the isolation valve. IDs (Independent Doubles) have the same advantage. Progressive Equalization provides the option to access gas that would not be available with a catastrophic failure with IDs though... depending on the failure of course.

Valve up or down is a separate consideration, except for faster and more comfortable valve access. Surprisingly, you can still hear the sound of a high pitched slow leak with valves down. Sound travels pretty well in the water. An extra few feet isn't significant, even with the added obstruction of the cylinders and protector.

The real show-stopper with valve-down is it is pretty high risk and inconvenient without a protector that also functions as a stand. The Cousteau team got by fine for decades without them but can you imagine losing your balance on deck and falling on your butt? A jet pack sounds fun, but not this kind! You also need one protector for every set of doubles so the cost is a consideration. No system is perfect.

BTW, I don't do "technical dives" but I have been doing staged and linear decompression dives for decades before anyone came up with that silly moniker.

There are no-decompression dives and decompression dives of progressively greater complexity culminating in saturation diving, which is the most technically complex I have seen. You can also perform very technically complex work underwater without being committed to decompression. Using an eCCR at 40' is technically very complex compared to most open-circuit decompression dives. "Technical" is a very poor choice and the definition is so fuzzy it is almost meaningless.

 

[PfcAJ]

Are you not concerned with the need to donate gas and shortly thereafter end up with your buddy (or you?) out of gas?

 

[Akimbo]

Are you not concerned with the need to donate gas and shortly thereafter end up with your buddy (or you?) out of gas?

I don't understand why anyone would be. Sharing gas is a "head for sunshine" event. I have the option to leave the isolation valve open at any point in the dive, which I can open in less than one second. I don't donate the regulator on my right/online cylinder so I would be the first to suck a vacuum. That's a pretty solid reminder to reach back and open the valve.

If the ONLY problem is your buddy running out of gas you still "should" have plenty onboard if your gas planning is sound. Of course, your buddy would not run completely out of gas using progressive equalization even if they screw up and forget to monitor their SPG. They might have a sudden major leak, but half their remaining gas would be automatically isolated for them -- no quick thinking or reflexive action accompanied by constant drills required. You are already used to operating the isolation valve several times per dive.

There is an argument for equalizing and shutting the isolation valve at the start of an air sharing event -- but it really is a last-ditch multiple failure consideration. If everything really goes sideways, both divers running completely out of gas at the same time means you will probably both go hyoxic and float away. At least you stand a chance of being revived IF your buddy can get your unconscious butt to the surface.

You are also not "required" to wait until your online cylinder is sucking hard before equalizing; assuming you can see your pressure readout and it is accurate. You have the option to breathe it down to any pre-determined pressure before equalizing. For example, if you want to play the "rule of thirds".

Progressive equalization does not use more or less gas than any other configuration. The exception is that you end up with more gas isolated for use in the event of a major gas leak on one side. It's all a game of options and probabilities that have to be considered when developing your dive plan. In my analysis, progressive equalization has a lot more options and is a far more forgiving of human and hardware failures. It also requires more than just memorizing procedures to take full advantage of the technique.