Diving with redundancy.

[Wathdoc]

Redundancy in any aspect of dive gear is nice in principle, but in practice a question one might ask is whether the risk outweighs the hassle. Risk is sometimes defined as the combination of the probability of harm and the severity of the harm if it occurs.

The hassle here is having to own, transport, and maintain yet another first stage. Not a major hassle, but still, part of the beauty of recreational diving is its simplicity. The goal is to maximize fun while staying safe enough. "Self-reliance," as you mention, is good, but improving buddy procedures is the more standard way--that is, the way the major dive agencies teach--of dealing with problems. Before resorting to more gear, consider whether the kind of diving you do is amenable to improved buddy procedures. If what you are doing is more like solo diving than what the dive agencies classically consider "recreational" diving, then maybe take a course in solo diving and gear up like a solo diver.

How often do first stages (that have been properly maintained) fail in a way that suddenly cuts off your gas supply? I would say extremely rarely, unless you're diving in near-freezing conditions, in which case I would argue that much like the solo diving I mentioned above, you're no longer doing classic "recreational" diving; now you need to think more like a technical diver, and yes, that means redundant gear of some sort. You probably should NOT rely on a buddy for dealing with first stage freezes, because two divers breathing off the donor's first stage is likely to result in the donor's first stage freezing up as well. For redundancy, H-valves seem more popular in Europe, whereas ponies are more popular in the US.

Not in the UK, it's pony or doubles all the way.

 

[The Chairman]

nd all of a sudden I have a first stage failure

It's been my experience that 99% of first stage failures happen on the initial pressurization or the first breath. That might be a conservative number. No, I haven't witnessed 100 first stage failures, but then I've never seen one fail at depth, either. I've seen some IP creeps, but breathing off of the reg will usually keep that under control. Most failures at depth seem to involve the HP hose or fittings.

There's really no need to overthink this. Your training taught you several methods to deal with OOA, all of which are still available to you. Since the most common failure is a ruptured hose, you really have a lot of time to deal with such a failure. You probably have enough time to make an ascent with such a failure if you act decisively. No, you won't be able to do a safety stop, just make your way on up.

Realistically, you can't prepare for each and every possible failure on a dive. Once you've covered that 99%, you'll have to rely on your training and creativity. That's really not such a big deal, is it?

 

[Angelo Farina]

No, I haven't witnessed 100 first stage failures, but then I've never seen one fail at depth, either.

I have seen several times (a dozen, perhaps) the yoke O-ring being extruded, causing a massive air loss, at depth.
Often caused by an impact on the reg, or it being not mounted properly, or simply a worn O-ring.
It is not a true first stage failure, indeed. If acting properly and quickly, it can be solved underwater, even in the case you have only one reg: close the valve, dismount the reg from the first post, mount on the second post and open the second valve.
Water will come inside it, causing the need of servicing it thereafter, but this way you save the dive.
I agree that most of the times the O-ring explodes when opening the valve, on the boat, or perhaps just after entering the water. But, as said, in at least 10-12 cases I have seen it exploding at depth, and once it happened to me.

 

[MichaelMc]

However the point for me is another: when I RENT a cylinder, do I ask for one with double posts? the answer is ALWAYS.
The cost for the rental is the same. The added redundancy is a benefit, even if using a single first stage (of course with DIN mounting - with Yoke mounting it would be unsafe using only one first stage). The additional weight of the valve saves one lead in the belt. I really do no see the advantage of renting a cylinder with just one post...
Why the hell people rents (or buy) them?

I agree H/Y is more redundant than single post, and in the same general package, one cylinder.

Yet training here does not emphasis reaching and closing valves, except at the solo or tech level. So most would be unlikely to solve the problem by closing a valve. Vanishingly few by swapping valves.

I’ve not seen H/Y valves here. Perhaps a few are in the back room. The rentable options you know you can get tanks for are: independent doubles with a strap kit, sidemount, or ones own pony.

 

[Angelo Farina]

I agree H/Y is more redundant than single, and in the same general package, one cylinder. Yet training here does not emphasis reaching and closing valves, except at the solo or tech level. So most would be unlikely to solve the problem by closing a valve.

Of course this is true, also here teaching agencies stopped teaching how to manage quickly your valves more than 30 years ago, when DIN regs became common.
However, the most common failure I have seen is damaging the KNOB of the valve, when the cylinders falls.
If the cylinder has just one knob, and there is no replacement aboard, your cylinder becomes useless.
If it has two knobs (two valves), you simply use the second.
Same for the Yoke O-ring. It usually explodes on the boat, when opening the valve. If you have a replacement at hand, you change it and there you go. But it happened to me at least three times that there was no spare O-ring available on our Zodiac (or that they had already been used).
Again, you just move the reg on the second post and you are ready for diving....
I really do not see why a cylinder should be equipped with a single-post valve. They should be simply forbidden, in my opinion, for cylinders of more than 8 liters...

 

[markmud]

Open water redundancy? Use an AL40. Solo, it should be enough to get to the surface unless you screwed up and went into big deco. With a buddy? know how to deploy it so that it's clipped to your buddy's kit after they are comfortable breathing off of it for a minute or two. Don't use a crap regulator

Hi OP,

The Big Kahuna has it right. But...for me I use different size ponies for different occasions. For rec buddy diving, which is a clearly defined standard that nobody follows to a "T", I use a 6cf pony. It travels easily on jet liners and I fill it with a transfill whip at my destination.

For true solo dives in benign conditions where my depth does not exceed 100 feet, and there are no known entrapment issues, I use a 13cf pony. It also travels well on jetliners.

If your destination has 40cf bottles, use those. They sling just as easy as a 13cf or 19cf.

If you want true redundancy, either doubles or a pony.

You’re diving locally? If so, pretty similar water temps to what I dive. I don’t know if anyone who uses a H-valve locally. Doubles or pony (usually AL40) here.

And, yes, I see a number of locals here who dive doubles for recreational profiles.

An H valve gives you a second regulator but not redundant air. So it’s not a bad thing to use, but doubles, sidemount, or pony are better options Imho.

All of the advice above is spot-on. Ponies are super easy. Train with one though. Remember, your power inflator won't work if your primary fails and you are performing an emergency ascent directly to the surface. Orally inflate if you need more buoyancy.

Cheers,
markm

 

[MichaelMc]

I really do not see why a cylinder should be equipped with a single-post valve. They should be simply forbidden, in my opinion, for cylinders of more than 8 liters...

Requiring two posts per cylinder would be a royal pain and cluster in sidemount . DIN is cleanest to manage, yoke works ok. Stage/deco bottles seem similar. Independent doubles might be ok.

 

[Lorenzoid]

Not in the UK, it's pony or doubles all the way.

Evidence that this is a better way to do recreational diving than proper utilization of the buddy system? Do BSAC teach doubles and a pony from the get-go? A new diver trained that way isn’t going to be able to bring doubles to his Red Sea liveaboard. In my opinion, teach new OW divers what is most universal, and then for those who want to dive under specific local conditions, teach those variants, including pony or doubles where appropriate.

 

[Edward3c]

Evidence that this is a better way to do recreational diving than proper utilization of the buddy system? Do BSAC teach doubles and a pony from the get-go? A new diver trained that way isn’t going to be able to bring doubles to his Red Sea liveaboard. In my opinion, teach new OW divers what is most universal, and then for those who want to dive under specific local conditions, teach those variants, including pony or drysuit where appropriate.

BSAC teach single cylinder (with or without dry-suit) for Ocean Diver and Sports Diver training. Once the Sports Diver qualification has been signed-off then the individual can attend:
* a twin-set course (a pony is only one of a number of configurations that qualify as twin-set (its only the commercial exploitation that separates side-mount as a separate course),
* accelerated decompression procedures (ADP) - a requirement to do trimix courses,
* instructor foundation course,
* begin rebreather training.

 

[W W Meixner]

I was just curious what others thought about diving with an H-valve while diving recreationally? Seems like a good idea to me for redundancy and self-reliance, but I’m not sure of the downside if any.

Thanks in advance for your insight.

Kevin

OW...

As has already been stated...with an H valve fitted single cylinder...you're getting double the first and second stages...but not redundancy...

Your redundancy has to be a complete separate/stand alone system with enough breathing gas to get you to the surface safely...fulfilling all stop/deco obligations...cylinder/valve/1st stage/second stage/SPG...plus any other necessary attachment hoses...

That redundancy may be doubles with an isolator valve...or any configuration of slung cylinder...if you're speaking strictly NDL recreational diving...any small cylinder from a 19 cu ft to a 40 cu ft should suffice...and again taking all your committed obligations into consideration...and if required factoring in dry-suit inflation...if your bailout cylinder is being used for that purpose as well...

Check out DGX for small cylinders/bailout reg sets/sling harness hardware...

W.M...