necklace not annoying?

[divad]

With all the talk here about wanting identical 2nds for primary and alternate, and the desire for redundancy, what I was wondering was why that setup instead of identical 2nds, both on 40" (or whatever) hoses, both under the right arm, one into a necklace and one into the diver's mouth? Then the 2nds could be used interchangeably and if a panicked OOA diver just grabbed one of your regs, it wouldn't matter which one they grabbed.

Because you want to be sure that they can't get away with what you know to be your backup regulator.

 

[halocline]

With all the talk here about wanting identical 2nds for primary and alternate....
and if a panicked OOA diver just grabbed one of your regs, it wouldn't matter which one they grabbed.

The talk about 'identical 2nds' is something different. In the old days, most divers used a lower quality 2nd stage for the alternate, mostly to save money. Lots of people still do. Some people think that in an emergency, you want to be breathing on a 2nd stage that's as good as your primary 2nd, so why get a low-quality alternate? There is some sense to this, but it doesn't mean you need 'identical' it just means you need 'as good as' or even 'good enough' for an alternate 2nd stage. It has nothing to do with hose routing.

Regarding the panicked diver grabbing a 2nd stage, there is a theoretical point that since an OOA diver's behavior could be unpredictable, it might be best to have enough hose length on all 2nd stages to accommodate the panicking diver. But in reality, a panicking OOA diver is most likely to go for the reg in your mouth. It's happened to me twice, both times when I was in my DM internship years ago. One of the panicked divers was another DM. Pretty sad....but that's another story.

Anyhow, as mentioned, in addition to air-sharing convenience, you want a hose routing that is streamlined, less likely to present an entanglement hazard, and comfortable. It turns out that for many people this is a 5ft primary hose routed hogarthian-style and a 22" (maybe 24" if you're a big brute) alternate hose. Two long hoses would be tough to stow and deploy in a convenient and streamlined manner.

The cave diving community has really figured this stuff out, because by necessity they must dive in a very streamlined manner and have the ability to share air single file in restricted areas. Hence the 7ft hose. In open water you don't need to go single file so you don't need a 7 ft hose, but the other nice things about the routing, especially the real streamlining and comfort, can be had with a 5ft hose routed under the right arm, across the chest, over left shoulder, behind the head, and around. Make sure you try this type of set up before you decide what to buy.

The 40" hose on an elbow is not as streamlined or as comfortable in my opinion. And you have the elbow, which can be a little awkward for air sharing.

 

[PfcAJ]

The unbalanced 2nd thing was (is) due to reliability and lack of freeflow when scootering. I've got a bajillion regs and always used an unbalanced 2nd for my backup. Breathes fine (even at depth). Maybe not as good as a g250, but that's ok. The things never leak or give me an ounce of trouble which is exactly what I want in a backup.

Stuartv, the idea with the necklace is that the reg is fixed in place. If it can pop out of the necklace when someone pulls on it, it can pop out at times when you don't want it to (that's bad). Rig it like evad showed and it won't pop off the bungee no matter what.

 

[halocline]

The unbalanced 2nd thing was (is) due to reliability and lack of freeflow when scootering. I've got a bajillion regs and always used an unbalanced 2nd for my backup. Breathes fine (even at depth). Maybe not as good as a g250, but that's ok. The things never leak or give me an ounce of trouble which is exactly what I want in a backup.

I have some unbalanced 2nd stages as well; they work just fine. I have always heard that the old-school idea of balanced primary/unbalanced alternate was so in the event of an IP spike, the alternate would start to flow before the primary. They are more IP-sensitive. This would then give the diver some 'warning' that a HP seat failure was imminent and it's time to end the dive.

The simplicity and free-flow resistance is only of benefit if the simple design is actually more reliable than the slightly-less-simple balanced 2nd stage, and if the unbalanced 2nd stage is tuned with a little higher cracking effort to withstand the pressure of current against the diaphragm. In reality, adjustable 2nd stages (or at least adjustable venturi assist) are likely a better choice for free-flow resistance, and the best of the classic barrel poppet balanced 2nds (like the G250) are every bit as reliable as the simple downstream 2nds.

I love the old SP 109 metal case regs for alternate 2nds, but I usually put the balanced poppet in them. I find they hold a tune better. I have a few that I haven't rebuilt in probably 4-5 years, I lose track. But they still work beautifully.

 

[PfcAJ]

I have some unbalanced 2nd stages as well; they work just fine. I have always heard that the old-school idea of balanced primary/unbalanced alternate was so in the event of an IP spike, the alternate would start to flow before the primary. They are more IP-sensitive. This would then give the diver some 'warning' that a HP seat failure was imminent and it's time to end the dive.

The simplicity and free-flow resistance is only of benefit if the simple design is actually more reliable than the slightly-less-simple balanced 2nd stage, and if the unbalanced 2nd stage is tuned with a little higher cracking effort to withstand the pressure of current against the diaphragm. In reality, adjustable 2nd stages (or at least adjustable venturi assist) are likely a better choice for free-flow resistance, and the best of the classic barrel poppet balanced 2nds (like the G250) are every bit as reliable as the simple downstream 2nds.

I love the old SP 109 metal case regs for alternate 2nds, but I usually put the balanced poppet in them. I find they hold a tune better. I have a few that I haven't rebuilt in probably 4-5 years, I lose track. But they still work beautifully.

The early proponents of the bungeed backup/longhose had 2 first stages anyways. An IP spike on the left reg (backup) wouldn't do a darn thing to the primary/ balanced adjustable reg.

My issue with detuning the balanced adjustable regs with the adjustment knob is the pressure and engraving on the seat. Then you back it off for easy breathing, but you're also probably induced a slight leak in the process.

 

[DeepSeaExplorer]

"mask on the forehead is a sign of distress" is right up there as one of the top scuba myths, along with "back the valve off 1/4 turn so the valve doesn't get stuck" and "ascend with your bubbles" and "face your SPG away from you in case it explodes" and "you can't get bent on an AL80 because it does not hold enough gas to keep you down long enough."

There is (or was, a long time ago) a gain of truth in these myths, but not with modern equipment and modern diving.

(I can hardly wait for all the negative responses.....)

Ok, I'll bite...

The valve 1/4 turn thing wasn't invented by divers. It's a standard industry practice that was inherited by divers. It's to prevent someone from using a pipe wrench to open a "frozen" valve that's already open. Imagine you work in a big plant and the control room sends you down into the depths of the plant to open a valve that hasn't been used in years. You try to turn the valve, but it's frozen so you get out your big pipe wrench and go to cranking on it. It won't budge, so you really lay into it. Then you think, I'll rock it back and forth and try to free it. That's when you realize it wasn't frozen at all - it was already fully open. But, now you've wasted an hour of everyone's time screwing around going to the tool locker to checkout a pipe wrench, etc. and damn near bent the valve.

So, it's a legitimate thing. And, despite the stories on SB no one has ever died by using the 1/4 turn method. Now, there may be some folks that can't tell the difference between a 1/4 turn and 3 turns, but that's different. It also works well if you're checking a bunch of tanks to make sure they're on. If you try to open a tank that's jammed all the way open, it takes a second to figure out if it's stuck closed or jammed open. The 1/4 you feel quickly tells you it's open. Who knows more about valves, Pipefitters or Scuba Instructors?

 

[halocline]

The early proponents of the bungeed backup/longhose had 2 first stages anyways. An IP spike on the left reg (backup) wouldn't do a darn thing to the primary/ balanced adjustable reg.

My issue with detuning the balanced adjustable regs with the adjustment knob is the pressure and engraving on the seat. Then you back it off for easy breathing, but you're also probably induced a slight leak in the process.

I was not talking about doubles use nor was I arguing that there's much validity in the use of unbalanced alternates for that reason.

I have to disagree about the adjustment knob causing leaks, in fact IME it helps prolong the LP seat life. I leave the adjustment knobs all the way out to save the seats except when I need more resistance. Non-adjustable regs, especially unbalanced ones, have a constant pressure on the seat that causes more wear.

 

[BUDMANOK]

None - Not Certified

Am I missing something? the OP has this as his status. I mean should he even be worrying about this? It seems like there are a lot of other more important things to worry about. Like getting certified?

 

[Lorenzoid]

Am I missing something? the OP has this as his status. I mean should he even be worrying about this? It seems like there are a lot of other more important things to worry about. Like getting certified?

Judging from his previous posts, "should" is not in his vocabulary.

I think it's the engineering mindset. My father-in-law, a former engineer, resisted using the Internet until he had first researched packet switching, understood the inner workings of the thing, decided what browser and e-mail client would be optimal, etc.

 

[stuartv]

Am I missing something? the OP has this as his status. I mean should he even be worrying about this? It seems like there are a lot of other more important things to worry about. Like getting certified?

I am doing my OW dives this weekend to complete my OW certification. This question partly came from seeing what some of the instructors were using doing my confined water exercises last weekend.

I think it's the engineering mindset. My father-in-law, a former engineer, resisted using the Internet until he had first researched packet switching, understood the inner workings of the thing, decided what browser and e-mail client would be optimal, etc.

LOL! That's hilarious! I'm not quite that bad, though. I wouldn't resist scuba diving until I understood every detail of how it's done. I'll do it the way I'm taught, in the meantime.