Independent Doubles vs. Isolated Doubles

[Spimon]

I believe this is the video you're referring to:
YouTube - Cutting a Scuba Divers Regulator Hoses

 

[Nemrod]

The question on the BC. On independent doubles you do NOT have twin power inflators. If you were to loose a tank (it's gas) and it were the one with the power inflator hose then you just adjust your bouyancy using the oral inflator. You don't run two LP inflator hoses. If you had a twin bladder wing you could set it up for twin inflators but that is a lot of complexity to avoid having the possibility of using the oral inflator.

N

 

[TSandM]

To answer the question of how long it takes to close a valve, GUE requires that a Tech 1 student be able to close a valve in less than 15 seconds.

Saying manifolded doubles offer no advantage because the people diving them can't reach the valves is condemning a perfectly good piece of equipment for the user's lack of skill.

You're never going to find a study of comparative failure rates, because failures are luckily uncommon, and there is no central reporting. But I'm happy with my analysis, which says that things that move or are moved (i.e. regulator pistons, DIN o-rings, regulator hoses, etc.) are more likely to fail than things that don't move (i.e. manifold o-rings). And I like the idea of maintaining access to all of my gas, and will like it even more if I have to shut a post 1000 feet back in a cave

 

[peterbj7]

Any real reason to use independent over Isolated, not looking at the cost for either.?

I haven't read this thread but the title intrigued me. Isolated doubles ARE independent doubles, so IMO the question is meaningless. Does the OP mean Manifolded Doubles vs. Independent tanks? In which case there certainly are good reasons for going the manifolded route.

 

[peterbj7]

On independent doubles you do NOT have twin power inflators ..... You don't run two LP inflator hoses. If you had a twin bladder wing you could set it up for twin inflators but that is a lot of complexity to avoid having the possibility of using the oral inflator.

That is an unwarranted generalisation. You most certainly CAN have two power inflators with independent, or manifolded, tanks and I've often done it, and I've seen others doing it. I see very little added complexity. Yes, that was with a twin bladder wing, which is what you should be using for tech diving in warm water to give you usable redundancy.

 

[peterbj7]

I am now reading back through this thread, and I find aspects fascinating:-

talking with a buddy last month, if you dive your tank down to 500 psiand finish our dive then...with independant doubles you come back with 1000psi of safty air;
with manifolded dubs, both tanks come down to 500 psi and you get to be in the water that extra 500psi.

How can anyone have at least 100 dives and spout rubbish like this? Actually, how can anyone have any physics education, even the miniscule amount in a basic diving course, and say it? It's not a question of getting the maths wrong, but of fundamentally not understanding what's physically happening.

 

[peterbj7]

OK, my last contribution here, for the time being. Has anyone ever had a tank neck O-ring fail during a dive? I don't mean leak a little as I had that once, I mean really blow. I've never even heard of it.

 

[Nemrod]

That is an unwarranted generalisation. You most certainly CAN have two power inflators with independent, or manifolded, tanks and I've often done it, and I've seen others doing it. I see very little added complexity. Yes, that was with a twin bladder wing, which is what you should be using for tech diving in warm water to give you usable redundancy.

I will stick with what I said. If you want multiple LP inflator hoses and two wings, go for it, it is not needed, especially in warm water diving which you mentioned. You can orally inflatea BC/wing without a power inflator enough to control bouyancy, I can anyway, even if you cannot. N

 

[ianr33]

OK, my last contribution here, for the time being. Has anyone ever had a tank neck O-ring fail during a dive? I don't mean leak a little as I had that once, I mean really blow. I've never even heard of it.

Never happened to me but seems that it can happen
The Deco Stop

The full thread is The Deco Stop

Lots of interesting advice in that thread. DO NOT lubricate the tank neck O ring and be certain to use 90 durometer.

 

[peterbj7]

I will stick with what I said. If you want multiple LP inflator hoses and two wings, go for it, it is not needed, especially in warm water diving which you mentioned. You can orally inflatea BC/wing without a power inflator enough to control bouyancy, I can anyway, even if you cannot. N

Oh dear, more attempted point scoring. Why would you assume that I don't know how to inflate a bladder orally, just because I prefer to do it with tank air?

And why do you say that two wings (not that that is what I said - I said one wing with two inflatable bladders) are unnecessary especially in warm water? In those circumstances you typically have no other usable redundant buoyancy - what do you do if your sole bladder ruptures or otherwise won't hold air? I know of deaths specifically because the people concerned did not have redundant buoyancy readily available to them. I had to recover the body of one of them, from 125mtr.