Independent Twins

[wedivebc]

I know it's not a necessity to be able to shut down a tank with independant doubles'
but how many use tanks with right and left valves?
How easy would it be to get at the valve handle centered if you were using 2 rights?
I favor a manifold.
If it comes down to the few dives where I needed the extra air (vacation) I will just sling it.

Actually the handle is located quite close to where the isolator on a manifold usually resides. I can shut mine down and I use a drysuit with dry gloves and cuffs (read restricted movement) but like you say 'it's not a necessity'. That means my life does not depend on me being able to reach my isolator in a restricted area ,say of a wreck.

 

[WarmWaterDiver]

The regs are more protected from bumping, etc., if both first stages are between the tank valve and the diver.

Bumping? Against the diver's head? Or against the diver's environment?

If one is using say an Atomic or Scubapro first stage (two popular brands that come to mind), that incorporate a swivel turret, and have these mounted turret up, is this statement true?

I can't imagine sufficient force to dislodge a first stage from a tank valve, when pressurized, that could result from diver swimming and then colliding with something - especially if using DIN valves. Surely however there are cases of folks who have done this though - but there was probably more to the story, much like a previous post on this thread. Maybe taking a scooter at full speed and ramming themselves through a low clearance opening? Or using a yoke style first stage that the yoke design is less than 'robust'? Something else as part of the story that wasn't illustrative of intelligent risk management to begin with?

Again, I don't dive hard overhead environments. But, if that's the real concern, and safety is the real driver in such a situation, why wouldn't sidemount be preferred to begin with? Then reaching the tank valves and 'bumping' risk could be controlled more maybe?

When I dive with slung deco gas, that's not something I look for - keeping the sling bottle valve and first stage on the sling bottle oriented a certain direction (one and only one) relative to my body at all times during the dive. Maybe some folks have such a concern???

Could this be mitigated by 'cobra guards' or similar? Is this unsurmountable enough to say 'no one should ever do this'? Or is this truly creating additional hazard?

Or is this another 'sacred cow' of 'one and only one way'? I see these days even advertisers don't use the phrase 'one size fits all' any more - at best it's 'one size fits most'.

Much like wedivebc, reaching the tank valves haven't been a problem for me - but if it were, I haven't chosen put my gray matter on the shelf. I might think about things and ask "why not . . . "

Oh, the other way I earn my bread and butter is for 'thinking outside the box' and 're-examining paradigms'. It's not for everyone, of course, or there wouldn't be a demand for such.

Back to different 'strokes' for different folks . . .

 

[MikeFerrara]

For team diving situations I'd never part with my manifold. Having access to all your gas through either reg can be a VALUABLE advantage. There are a few failures that can cause total gas loss with a manifold but they aren't likely and I've never actually heard of them happening. Being able to quickly maipulate your valves shouldn't be an issue. If you're doing overhead dives (real or virtual) you should have already mastered this and it shouldn't take any where near 30 seconds to shut down one valve...provided you know which valve needs to be shut down.

For solo diving or applications like sidemount independants may be the way to go because the possibility of a total gas loss, though remote, would certainly kill you. With side mount the a key advantage of course is the mounting itself and if I were to dive independants I don't see a reason to bother putting them on my back...ever. With the valves in your armpits you can not only reach them easily but you can also inspect things visually which makes it nice if you have to pull a reg off or something. As a sidemount cave diver frined of mine says...valves belong in your armpits. LOL

Sidemount divers don't plan on having to share gas but I do know of a case where it happened. A lone sidemount diver was returing from a survey dive through a HIGH flow restriction. The flow jammed him into a tight spot and he was temorarily stuck. It was also time for him to be switching tanks but knowing he had plenty of gas in the other one he decided to wait til he got unstuck. He eventually got himself unstuck minus his reels, missing a fin and very low on gas in the tank he was breathing. I have some video taken by a diver that was on the other side of the restriction BTW. When he emerged from the restriction and switched tanks he found the other non-functional. Luckily another diver from the survey team was there so he got gas. Things got even more complicated in that one of the other divers regs was also nonfunctional so the two sidemount divers actually had to buddy breath off a single reg for a time wile they got another reg working. crawling through tight sandy places can be murder on equipment and had they not been able to get another reg working they might not have both made it to the next stash of stage bottles.

 

[DA Aquamaster]

I have never yet used independant doubles with a 'right' and 'left' hand tank valve - in fact, I don't think I've ever seen any 'left' tank valves mounted on rental tanks anywhere we've traveled, unless they were already connected to a manifold with center isolator.

But, if one had an extreme concern with this, why not mount the left tank 'backwards' from the right tank? Is it some special 'rule' that both first stages must reside between the tank valve and the diver?

I have mounted the left tank backwards in situations where the rental tanks involved had valve/handle designs that were hard to reach or operate. The reg does stick out the back a bit more but if you are using a DIN connection, it would take a lot of abuse to cause a problem.

 

[jerryn]

How could you tell all of this if you just happen to come up on the situation? Sounds fishy to me.
As was already stated, they screwed up long before you came upon them with poor gas management.

Jason

I know the thread has moved on, but since Jason thinks this sounds fishy, let me answer his question.

When I came upon them I asked if they were okay. The donating diver's okay seemed tentative, so I checked the spg on the donating side. It was tucked back and not so easy for him to see. When I saw it was at about 200 psi -- I offerred my 2nd stage to OOA. The donator waived bye and headed for the surface. After the completion of deco I surfaced with the OOA diver. And then I asked questions in a debrief. Not so hard to know all of this... and we did not see any fishy's.

But too the point, with independent twins, if you are in an air sharing situation, you have a compounded gas management problem. This is because it is going to be rare when you have the same amount of air in both tanks. Early in the dive this will be no problem. Late in the dive, as in the incident I related, it could be. Just something to think through for those who like to dive with independent doubles. (of course you could add an octopus to each of the regulators).

Jerry

 

[wedivebc]

I know the thread has moved on, but since Jason thinks this sounds fishy, let me answer his question.

When I came upon them I asked if they were okay. The donating diver's okay seemed tentative, so I checked the spg on the donating side. It was tucked back and not so easy for him to see. When I saw it was at about 200 psi -- I offerred my 2nd stage to OOA. The donator waived bye and headed for the surface. After the completion of deco I surfaced with the OOA diver. And then I asked questions in a debrief. Not so hard to know all of this... and we did not see any fishy's.

But too the point, with independent twins, if you are in an air sharing situation, you have a compounded gas management problem. This is because it is going to be rare when you have the same amount of air in both tanks. Early in the dive this will be no problem. Late in the dive, as in the incident I related, it could be. Just something to think through for those who like to dive with independent doubles. (of course you could add an octopus to each of the regulators).

Jerry

If you read mine and others description of gas mangement (which mostly seem to agree on protocol) this is never a problem since the only time your tanks will have the same amount is at the turn point and at the end of the dive. Any other time you have more than enough gas to get you and your buddy home. Even at the turn point you have just enough.

 

[Hoosier]

Jerry,
NO! You totally misunderstood the gas management. You only calculate the total capacity of air from both tanks. Like other members have already posted, each tank will hold 1000 psi at the end of the dive based on the gas management. In my case, I wrapped up the dive at 500 psi each tank because I only use the independent double up to 60 ft (the max. bottom) at the local quarry.

I am not sure how deep diving situation you are talking about. But, 1000 psi each tank is more than enough (800 psi) for the emergency exit from 130 ft including the safety stop. In addition, if you plan to do a deco diving from the beginning, where do you use the deco tank in your scenario? Please nobody said that the independent double is totally able to replace the manifold double. The point is that the independent double has its own benefits (flexibility, convenience, and safe) and it is more than enough for the recreational deep diving.

 

[jerryn]

Hoosier,

I agree with you. For recreational profiles, leaving the bottom at 1,000 psi in each tank -- say double 65's or larger -- would provide sufficient air for the diver and the dive buddy to get to the surface with five minutes of safety stops from 30' up. This should not be a problem.

The incident I brought up was one in which the OOA diver had a deco obligation, and the two divers were not dive buddies. I don't know what the pressure was on the ID diver's tanks when he left the bottom.

My only point, is that this is something to think about -- if you are considering ID as the original poster was -- you need to know what the limitations are. Same is true with manifolded doubles -- if you can't reach your valves and shut the posts or manifold down then this may not be a good way to carry your dive gas. Without knowing the potential problems you cannot take do the dive planning to avoid them.

Jerry