Two 2nd stages, but only a single first stage?!?

[eelnoraa]

TSandM its possible, but not probably
For that to happen wed have to screen divers the way we screen specops and thats not very inviting to me - although I WOULD have a lot more faith in any random insta-buddy hmmm...

I am in TSandM here, it is not only possible, but very probable in my case I call it "no stress" diving, it is just so much more enjoyable.

I think the original intention of the octo is NOT because any part of the regulator will fail (1st or 2nd stage). If anything, the octo is even more likely to fail considered how much it got dragged around. The octo is there so if you buddy is out of air, he/she can use it. In OP's case, if your 1st stage fail, you go to your buddy's octo and end the dive.

Having H-valve isn't necessary helping unless you also pratice the procedure to shut down the problematic valve. A true redundancy is a manifold double or a pony bottle.

 

[Tigerman]

eelnoraa TSandM said EVERYBODY IN THE DIVING WORLD.
Good for you that you can rely on the people you dive with, but they are NOT everybody in the diving world and scubaboard for that matter is not even representative of everybody in the diving world. The people hanging here are generally WAY above average interested in diving...

 

[Paulmal]

I dive an H-valve recreationally, on my personal tanks. The problem very few shops rent H-valves. I do it because it make switching between rec gear and my doubles alot easier and I don't see the point buying a desperate reg set for occasional Rec dives, when I go on vacation I have to reconfigure to use a single 1st stage. The other option is rent two tanks on vacation and dive side mount, but I prefer 2 5' hoses for side mount rather than a 36" and 7' that I use for back mount. The added redundancy of an H-valve is nice but not as good as doubles. If you are doing dives where you need total redundancy then I would use doubles or side mount not a single and a pony. It all comes down to how you want to spend your money. If you dive doubles/ H-valve learn how to use them properly is essential to realizing the added safety factor. If you can't shut down a valve/ isolate then you are no better off than having a single 1st stage. You have to do what gives you the warm and fuzzy.

Safe diving
Paulmal

 

[TSandM]

the alternate 2nd stage is not there for you, it is so you can provide redundant gas for your buddy. sometimes, when your buddy is not using it, you can; but that is not its primary purpose.

I think I'll start a poll on this. In my personal experience, I have FAR more often utilized my backup reg for myself, than I have needed to provide air to anyone else.

 

[Tigerman]

Ive used my alternate a couple of times and unfortunately my buddy has used it once - so far Im in the lead and I kinda hope it stays that way
That being said the times Ive used my alternate its been because
a) I use it from time to time to make sure it functions as it should - especially after having my regs serviced or
b) Ive made my primary freeflow due to so cold water I wouldnt be in it if it wasnt for the fact I got paid to - and then because Ive breathed it on the surface.

 

[fire_diver]

I think I'll start a poll on this. In my personal experience, I have FAR more often utilized my backup reg for myself, than I have needed to provide air to anyone else.

Can please give some of the reasons? So far in my diving I have only come to one situation that disabled only one second stage so I am curious what I'm overlooking.

 

[DA Aquamaster]

I think I'll start a poll on this. In my personal experience, I have FAR more often utilized my backup reg for myself, than I have needed to provide air to anyone else.

Same here. I've donated gas three times in 28 years in non training related OOA events (and none of them were ever my team mate/buddy, which is interesting...) but I've went to my back up a lot more often than that due to a wet breathing or otherwise less than optimally performing primary second stage.

 

[Scared Silly]

IIRC the history of the octo predates the SPG. Which BITD divers would check the pressure of their cylinders while dry to assure they where full. If they ran low once in the water they turned the J valve to use the reserve and ascend. If things went belly up divers would share air. That was SOP because there was no way to monitor air usage while submerged.

Then some one got the bright idea, instead of sharing air just use another second stage. In the mean time the SPG came into being. OF course all of the above relates to single regs and not double hose regs.

 

[DA Aquamaster]

SPGs were around back when the double hose was the major player in scuba. You could add a banjo fitting to most double hose regs (the yoke just needed to be big enough to make room for it) and attach an SPG, or you could attach the SPG to a number of valves that were made with a high pressure port in them. Technically speaking, adding an octo was not even possible on most regs. The DA Aquamaster could accommodate one by attaching it to an adapter on the hookah port, but that's a comparatively modern practice.

The first SPG appeared in the US Divers catalog in 1957, about the time that the first single hose regulators began appearing - but those single hose regulators only had a single low pressure port, so no octo capability.

In comparison, the octopus did not show up in the US Divers Catalog until 1973, 16 years after the SPG.

 

[halocline]

Why do most divers dive with a single first stage and dual 2nd stages? Are first stages so reliable that we don't need a back up? Why not dive with an H-Valve and run dual first stages? I'm putting together my first diving rig and am really considering an H-valve and two first stages or maybe going further and get a pony for a fully backed up system? What level of safety is enough? Maybe it depends on our confidence in our buddy too...

A few thoughts:
1. By far the safest way to dive, especially as a new diver, is with a reliable buddy. Please do not make the mistake of thinking that a redundant air source is a fitting substitute for a buddy. A redundant air source can't help you with a cramp, get untangled, check for problems in your gear, show you the way back to the boat, help you stay afloat on the surface, help you if you get sick, etc.....all of which are more likely problems than suddenly running out of air, assuming you're monitoring your air supply.

2. Certainly more regulators and more tanks or valves would provide more redundancy, but they also mean more complexity and require more task loading to safely operate. They also mean more chances for malfunction. Since the vast majority of regulator problems in water result in air flowing out, not in sudden loss of air, having an extra regulator means that you are, in fact, more likely to have a free-flow while diving. It's a matter of diminishing returns. First stage failures that result in immediate loss of gas are extremely rare. Probably (I have no statistics to back this, hence 'probably') the most likely form of air blockage in the first stage would be blockage in the filter. This is one reason I am opposed to the gimmicky "auto-close" features on some regulators that place a spring-loaded ball directly in front of the filter.

3. An alternate 2nd stage is there for two reasons; one is to share air, the other is in case there's a problem with your primary 2nd stage. There are relatively common problems, probably the most common is that the 2nd stage simply falls out or gets kicked out of your mouth. Another is leakage at the mouthpiece or exhaust valve that causes flooding of the 2nd stage and a mouthful of water. So it makes sense on several counts for each diver to have an alternate 2nd stage.