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...
Two 2nd stages, but only a single first stage?!?
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WeldonDowd
Contributor
I think mine is reliable; or I wouldn't dive with it. But if I was to venture somewhere where I couldn't cesa then I'd use two first stages on two tanks. You can go overboard with safety equipment for recreational diving. Look for the thread about the guy trying to route his pony bottle hoses. I'm on my phone so linking it is hard for me.
Tigerman
Contributor
First stage failures is not as common as 2nd stage failures and given that what we learn in "basic training" is that we should never dive alone and always stay close to our buddy, who also dive single 1st and dual 2nd the chance of not having an air supply are EXTREMELY low.
I HAVE seen issues where the first stage is rendered useless, but that was due to the o-ring on the divers tank blowing so it wouldnt have mattered if there was one or ten 1st stages connected..
Redundancy never hurts, but most dont solve it with more 1st stages than neccesary, they rather bring a pony or bailouts.. (Not the equine or bank types)
I HAVE seen issues where the first stage is rendered useless, but that was due to the o-ring on the divers tank blowing so it wouldnt have mattered if there was one or ten 1st stages connected..
Redundancy never hurts, but most dont solve it with more 1st stages than neccesary, they rather bring a pony or bailouts.. (Not the equine or bank types)
As we teach in open water . . . if you have a situation that lands you with no breathing gas underwater, the first choice is sharing gas with your buddy. If you have a reliable buddy, who is close enough to reach and who has maintained adequate reserves, it should be pretty much a non-event to get to the surface. This is the way I dive.
If you dive frequently with people who are unknown to you, inexperienced or of questionable training, you may well want to provide yourself with more redundancy. That's usually done via a pony bottle, and less often via an H-valve. With a pony, you have true redundancy, and with an H-valve, a tank o-ring failure can still leave you without anything to breathe. Given that rental tanks rarely come with H-valves, and that many people rent tanks or travel, I think the pony solution tends to be more common.
It is my heartfelt wish that everybody in the diving world were reliable enough that no one would feel the need to carry a redundant gas supply. It IS possible.
If you dive frequently with people who are unknown to you, inexperienced or of questionable training, you may well want to provide yourself with more redundancy. That's usually done via a pony bottle, and less often via an H-valve. With a pony, you have true redundancy, and with an H-valve, a tank o-ring failure can still leave you without anything to breathe. Given that rental tanks rarely come with H-valves, and that many people rent tanks or travel, I think the pony solution tends to be more common.
It is my heartfelt wish that everybody in the diving world were reliable enough that no one would feel the need to carry a redundant gas supply. It IS possible.
R
redacted
Guest
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.
Tigerman
Contributor
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...
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...
Glenn08
Contributor
I agreed with your reasoning and like twin 50's with a Selpac maifold, 2 first stages, but 3 second stages. For under-ice diving I want a back-up for me too. The octopus is on the back-up first stage, so ideally when sharing air each of us has our own first stage.
chrpai
Contributor
fire_diver
Contributor
Yes, but the MOST LIKELY situation is that the secondary second stage will be for an OOA or LOA diver, not you. If you lose the ability to breath from your primary, that situation is probably affecting the other.
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