Isolation valves or full independent Doubles

[TSandM]

Somebody ran a thread, a number of years back, on the Deco Stop, asking about who had had significant manifold failures. As I recall, nobody had.

The concept of manifolding the two tanks makes sense, since you can shut down a post to a regulator and retain access to all of the rest of the gas. Whether the isolator is useful or not is arguable; Jeff Bozanic has an oft-linked article about it, arguing that the isolator serves very little purpose. I have never heard of anyone having a failure which required isolation, and as I see it, the primary purpose of the isolator is to avoid gas loss from the "uninjured" side, if you misdiagnose the post you need to close. I've been impressed with the possibility of identifying the side of the leak, myself, and I have spent time with a number of people who have an order of magnitude more dives than I have, who have reported to me that they have never had a sudden, massive leak from behind their heads.

However, I will buy the argument that independent doubles mean you can never lose more than half your gas. But of course, any leak on one side then means you ONLY have access to at best half your gas. What I don't really understand is why someone who wants to dive independent doubles wouldn't sidemount, since in sidemount, you have effortless access to your valves, both visually and manually. The ONLY advantage I can see to back-mounted independent doubles is that you avoid the finicky idiosyncratic character of sidemount setups, which vary according to required lift and types of tanks, and each setup has to be independently balanced. It still seems the better strategy to me, compared with putting two tanks on your back and requiring the reach back for valve closure, without the advantage of a manifold.

The UTD system has some significant downsides, and in my opinion, the advantages aren't worth what you lose.

 

[Nemrod]

Because there is no reason on independents to close a valve. I would continue to breath the "injured" side until it is no more meanwhile heading to the surface. Since I am solo in such a rig that is where I want to be. If I ever do penetration diving again I would use my isolation manifolds. As to side mount I would as soon avoid that cluster.

N

 

[ajduplessis]

I was thinking on back doubles and side mount stages for a total of 4 bottles.

This is how I dive dive; and when going deeper, I sidemount 4 stages.

 

[Remy B.]

This is how I dive dive; and when going deeper, I sidemount 4 stages.

You mean 6 bottles total, right ?

 

[wedivebc]

Somebody ran a thread, a number of years back, on the Deco Stop, asking about who had had significant manifold failures. As I recall, nobody had.

I think that might have been me and it was prompted by a thread very similar to this. Only in those days there were people convinced I was going to die because I was diving independents.
Although I have not dived open circuit in about 10 years I still find these threads interesting.

 

[DaleC]

I think that the idea of just going sidemount if you want to dive ID's sounds easier in theory

I started diving single tank and then single/pony, but at times I wanted more gas than that so I started diving ID's. I kept my same wing and backplate and a band system that allowed for quickly swapping out the right tank for multiple dives. A good system for what I was doing ATT.

I also bought an isolation manifold and did that for a while. Still ok but I found I could only do one dive with them without dipping into reserve gas on the second (I own all 72's) so I really needed two sets of doubles or I had to swap from double to single on one trip (pita). I know someone will say I should dive bigger doubles to do two dives but that would be an outlay of at least 700-1000 for two large steel tanks and bands - all to do what I could do with my ID's already. Sometimes I get in the mood for them, and then I find myself breaking down those tanks again (like when I do a road trip and want to dive it all single vintage).

I took a foray into sidemount to see what that was like and generally enjoyed it but I used a DIY rig I cobbled together. It worked but if I were to default sm whenever I wanted twins I would probably invest in a proper rig, another big cash layout when you consider reg sets as well as the harness. And of course, some would advocate taking training which adds to the expense. It would also mean I dive BM single and SM double which is ok but it does mean flip flopping from system to system.

So, for me, ID's represent a simple way to get into doubles without making a large cash outlay for separate rigs. I use the same tanks, BP/W and reg sets, just swapping a couple of hoses. All the systems work, sm allows more specialized diving as do isolation manifolds. The more specialized you get, the more one particular set up wins through, but you also lose variability. Most doubles divers I know have two rigs, one single and one double, as well as multiple tanks to accommodate each. Cool, but I find I can dive single and ID doubles using a small stable of tanks, the same rig, and just a bit of reg swapping.

 

[ajduplessis]

You mean 6 bottles total, right ?

Correct.

 

[kwinter]

The ONLY advantage I can see to back-mounted independent doubles is that you avoid the finicky idiosyncratic character of sidemount setups, which vary according to required lift and types of tanks, and each setup has to be independently balanced. It still seems the better strategy to me, compared with putting two tanks on your back and requiring the reach back for valve closure, without the advantage of a manifold.

Backmounted tanks are more stable for lengthy walks or rocking boats. There are some very distinct advantages of sidemounted vs. backmounted independent twins. But there are also situations where backmounting is better. Different tools for different applications. If I were travelling to a remote location and doing boat dives or difficult entries, I would probably bring my backmount twinning rig instead of sidemount or rebreather.

 

[Remy B.]

I guess side mounts were borne in the cave diving, as for now I never had put doubles or side mounts on me, but it seems to me that it is less cucumbersome to have back doubles and sling stages, tha 4 side mount/sling bottles, I'm not to attracted to caves, look to me as liveless chambers with a nice architecture but without a purpose, I'm more in to wrecks, full of live, served a purpose, had a history.

Is because of wrecks that I'm pursuing tec training, God willing I will get there.

 

[wedivebc]

A jack of all trades is a master of none.

Not all styles of diving are suitable for all environments. If you want to limit the scope of diving experience based on your gear choices, fine but to suggest that someone who has a well rounded background in diving using various configurations is less a diver than you is completely ludicrous.