Sorry for the hijack, but I like being able to turn my air on and off on a single tank. I might consider switching to an upside-down tank configuration if a convenient and well-designed system were readily available (but it would have to be portable and able to be fitted to rental tanks).
And that's the show-stopper. Convenience, design, portability, compatibility and cost are the limiting factors.
It is possible to manipulate the valves on a single tank, providing you don't have injury/mobility issues with your shoulder/s or neck. I learnt to do shut-downs in doubles then quickly discovered that the same principles apply to a single tank. If you can get to the isolator on a set of doubles, then you can get to the valve on singles.
I still don't see that the benefits are worth the cost or money however. There's plenty of
skill-based solutions that provide the same end results.
I admit that the primary reason I like being able to reach my valve is to turn ON my air as part of my final pre-entry routine. It is the last thing I do before entering the water, and I do it after getting completely geared up. On boat dives, I usually do it while seated and equipment checks were all done earlier during tank setup. I know that my air is always off during the boat ride and while gearing up upon arrival at the dive site. When the boat crew offers to turn on my air, I just smile and do it myself.
I turn the gas on before kitting, but I do also complete a last-minute check once geared up (
never let it be said that human error can't occur - especially when responsible for/supervising trainees). I don't need an inverted tank to accomplish this - I doubt the average diver would either, if correct body mechanics are employed.
But to specifically address your “not needed” comments, there has been one occasion when I deliberately shut OFF my air underwater and turned it back on. I had descended to approximately 23 meters when my wing inflator hose “popped” off when I started to add some air...
I'd still say that inverted tank/s aren't needed.
1) You have a buddy, who can provide assistance.
2) Disconnected LPI isn't a critical failure - you can oral inflate.
3) You can practise and master 'reach back' manipulation of your valve/s.
4) In the worst case, you could remove and replace kit to achieve the same result.
All of which are
skill-based alternatives, that don't cost time, money or convenience.
Inverting a single-cylinder is an
equipment-based solution that addresses problems that are either (1) rare and/or (2) easily rectifiable through more simple methods.
Granted, this happened because the connection wasn’t fully seated in the first place, but at that point I had a choice to make: either return to the surface or fix it where I was. After establishing neutral buoyancy manually, I tried several times to reconnect the hose, but with the line pressurized, it just wouldn’t lock
LPI disconnect/connect is an open-water course skill (when pressurised). If you couldn't reconnect the LPI then there's a bigger issue to be addressed; either a training deficiency and/or an equipment problem. I assume you rectified that problem following the incident and it hasn't repeated?
It's certainly not a problem that
should repeat. Therefore, not a problem that needs addressing through expensive and inefficient modifications to the scuba configuration.
I got my dive buddy’s attention and he tried; still wouldn’t work. So, with his octopus standing by in case I needed it, I took a full inhale, reached back and shut off my air, reconnected the hose, and turned my air back on; all while drifting along in a mild current.
Off-topic, but I don't understand the reticence to utilise your buddies AAS as a first resort. I see a lot of divers exhibit this tendency. Is there some sort of stigma attached to using an AAS, even if temporarily? There shouldn't be....
In scuba training, we have students perform various drills without resort to using their buddies AAS (reg recovery etc). This is to ensure that they do have he 'bottom-line' capability of tolerating air depletion for a small timescale. It also provides further reinforcement for them to not hold their breath (blowing little bubbles). It's 'worst case scenario' training/preparation - but it doesn't mean that they should immediately resort to that worst case contingency in the future.
Twenty-five seconds without air, then the dive continued as planned.
I can think of more efficient and safe resolutions to that problem, but the end result was satisfactory. That said, I still cannot fathom why you would be unable to reconnect an LPI just because it was pressurised. I've seen a few LPI that were badly maintained...and had become sticky. However, that's a mechanical issue that isn't really effected by the pressurisation - they're a bitch to manipulate even on dry-land and without the air on.
If shutting off the air is the only thing that allowed you to reconnect, then the issue is beyond a 'sticky' connector.
No doubt, those of you who only dive with buddies will say that this would be a risky maneuver to try solo, and I agree. Still, for me it was a confidence-building experiment; I now know that if I have to do something like that myself, I can.
With respect to solo diving, then the diver concerned should have a redundant air source and the capability to problem solve and effect solution/s for any foreseeable contingencies. Shutting down gas is an option, because a redundant gas supply is accessible. In that respect, it is identical to buddy diving - where a redundant gas supply is accessible (buddies' AAS). A difference just exists in the fact that the solo diver would have to manipulate the valves themselves (reach back or kit removal) whereas a buddy team brings that immediate support - the buddy can do that for you.
Maybe it’s not a common occurrence, but I personally know of two other people who have lost their inflator hose connection while under water, and both returned to the surface.
Forgive my bluntness, but those individuals shouldn't have graduated from Open Water training. LPI disconnect/connect is a core skill that they should have 'mastered' in order to achieve their qualification.
