One or Two first stages?

[Compressor]

Nice discussion everyone.

 

[Oitzu]

Reading the standards it doesn't seem to be directly forbidden by the standards to use 2 first stages on a single tank.
I guess single tank with dual outlet is rather rare in the GUE-World so they don't really address it.
Also single tank with dual outlet with two first stages only makes sense when you can close each outlet separately, which is even more rare.

On a side note: Interesting that gue don't fully utilise work sharing on the two first stages in their configuration.

 

[Angelo Farina]

Reading the standards it doesn't seem to be directly forbidden by the standards to use 2 first stages on a single tank.
I guess single tank with dual outlet is rather rare in the GUE-World so they don't really address it.
Also single tank with dual outlet with two first stages only makes sense when you can close each outlet separately, which is even more rare.

On a side note: Interesting that gue don't fully utilise work sharing on the two first stages in their configuration.

Of course there must be regional variations. Here in Italy the standard singles are 15 liters, 232 bars, and are equipped with two convertible DIN/INT posts, each with its own independent valve.
Something like this:

Which is also quite cheap, at 289 € VAT included:
BOMBOLA SUB MARES 15 LITRI BI-ATTACCO PRODUZIONE 2019

This means that here using two independent first stages is not only possible, but quite easy, and I always considered it safer.
So I was wondering how something which is safer is not recommended by GUE, and if this was due to their "minimalistic" approach.
I see this as a typical American approach, which I also see reflected in resorts all around the world. When the diving center is run by Italian teams, they usually provide 15 liters steel cylinders with DIN double-valves and rubber foot. American-run diving centers provide smaller cylinders (12 liters, aluminium) with a single valve, possibly INT only, no rubber cover, so the usage of an octopus is mandatory and you need to always carry a DIN-INT adaptor if your regs are DIN.

 

[jale]

The rubber foot is not needed for alu tanks as the bottom is flat unlike the steel tanks (exept the "concave" version).
The Y or H valves are just a by-product of some (European) countries which often impose two first stages for leadership level.
Beuchat even produce a "twin regulator", 2 first stages in one single block, for people who think they still need two first stages on a single valve.
V-TWIN - Beuchat
I personally don't like these monster 15L tanks and I really hate the smaller version at 12L which is so unbalanced.

 

[Oitzu]

Up here in germany we also use independent double valves with two first stages on various sized tanks for cold water diving.
But as you already mentioned that isn't the norm everywhere in the world.

The main reason for the two first stages is that you can shut down one in case it "iced up".
Things like a "outlet splitter" on the valve or the "twin regulator" jale mentioned doesn't make any sense for that.

 

[Zef]

I regularly dive a tall 12L cylinder with an H-valve. In warmer months I will typically dive with one 1st stage mounted with a long hose to my primary 2nd stage and a short hose to my octo on a bungee necklace.

When diving in colder water (10c or less water temp), I reconfigure my reg set as follows:
1. Main outlet of valve - 1st stage with primary 2nd stage on long hose, LP inflator hose to wing, short HP hose to AI transmitter.
2, secondary outlet of valve - 1st stage with backup 2nd stage (octo) on short hose, LP inflator hose to drysuit, HP hose to SPG.

I have upper back problems and find that 15L steel cylinders and double setups cause me lots of upper back compression type discomfort.

The 12L cylinder at @200-232 bar is plenty of air for the length of dives I enjoy doing, does not cause my upper back to flare up in pain, and has decent buoyancy characteristics.

The double 1st stage offers me some protection against adiabatic cooling/freez-up since I am typically breathing off one first stage and inflating my suit off the other....I don't advocate using a a drysuit as a primary means to control buoyancy but find that comfort (warmth) and buoyancy control are overlapping concerns down to about 20 meters deep....so until that depth the suit inadvertently does double duty.

In addition, Since Autumn of 2018 I have been diving with an additional 3L pony bottle slung under my left arm for the SHTF scenarios all year round.

I don't dive anywhere that requires the use of two regulators, or independent air sources, but when diving in cold water on cold winter days it just makes sense to me to configure this way, especially since I have the gear available. Is it perfect? I would never argue that it is, but it works and adds a degree of safety.

-Z

 

[Angelo Farina]

The Y or H valves are just a by-product of some (European) countries which often impose two first stages for leadership level.

In reality we used to teach this also to students at first level, telling them that two independent valves and two first stages is safer. It was way before the Hogarthian or DIR approaches were established, so I was wondering why these approaches, which are declared to be for better safety, do not explicit mandate, or at least strongly recommend, the usage of this on single cylinders.
With an Octopus many things can happen, causing trouble to the single first stage. And you cannot simply "close the valve and use the other", as we were trained to do.
Regarding the size and form factor of various single and twin cylinders, I used almost any of them: in the seventies maximum pressure was 200 bar, so it was standard to use twin bottles of 10+10 liters, at 200 bar (that is 4000 liters total), with two independent valves and a semi-automatic mechanical separation system called the "reserve". There was no BCD, nor a back plate, the twin cylinders did have their own harness, making them to stay very close to you back, in a very stable and streamlined configuration.
Years later, after a few years with the first gen of BCDs (which were collar-shaped), American-style "jacket" BCDs arrived. They were not easily fitted on our 10+10 liters twin cylinders, so we switched to single cylinders, being just 15 liters at 200 bars, so 3000 liters instead of 4000. This required to reduce depth and bottom time, or to use an additional pony cylinder on the side for deco. We still continued using dual-valves, indeed.
The drag was increased enormously, the trim was much worst, and from the USA we also got the Jet Fins, which were much less efficient than the free-diving long fins we were used to employ (and that I continue to use also today, after a couple of years of bad adventures with the Jet Fins).
Fast forward to now: twin cylinders are still in use, but they call it "tech diving". They stay more far away from your back, as in between there is a plate and a wing BCD, so they are not as streamlined as our original ones. They are also often much larger than 10+10 liters, making them bulky and heavy to transport.
Now both me and my wife are grown old, we do not want anymore to dive down to 50m with deco.
So a single 15-liters cylinder is enough, also considering that now the pressure is 232 or 250 bars, so they give you 3500-3750 liters. They are still two valves: so why not using them with two independent regs? Is there anything making it a problem, instead of a benefit?
From all I did read in this thread, I see no real drawbacks in using two regs. So why isn't this recommended everywhere? Just for cost? Aren't shops always attempting to convince us to spend more money?
There is something I do not understand, why the hell an octopus is still considered the standard for rec diving?

 

[Zef]

From all I did read in this thread, I see no real drawbacks in using two regs. So why isn't this recommended everywhere? Just for cost? Aren't shops always attempting to convince us to spend more money?
There is something I do not understand, why the hell an octopus is still considered the standard for rec diving?

There is the prevailing mentality of "good enough"...are 2 1st stages an extra layer of safety? if you ask me my answer is yes. Is it necessary in recreational diving? if you look at the number of dives conducted with a single tank/single 1st stage configuration each day/week/month/year there is strong evidence that this configuration is "good enough" for recreational diving. If diving solo then you have other equipment needs, and if you are diving in cold water there are concerns that may have you choose differently as well, but for recreational diving in waters above 10c the "standard recreational setup" has proven reliable enough.

There is also the cost of maintenance. The overhaul cost of a reg set runs between 85 and 125 euros where I am and from reading through various discussions that price range is fairly common in the US/Canada as well. Using a 2 1st stages adds to that maintenance expense for the shop renting the gear or the owner.

For shops that rent gear, the addition of an second 1st stage to the configuration also means more hoses...these combined increases their investment. For divers purchasing gear, it inflates the already relatively high cost of entry to owning a complete set of gear.

One can always argue "but its safer", and one can always counter with "how safe is safe enough?"...

..."Safe enough" is a personal decision.

-Z

 

[Angelo Farina]

For shops that rent gear, the addition of an second 1st stage to the configuration also means more hoses...these combined increases their investment. For divers purchasing gear, it inflates the already relatively high cost of entry to owning a complete set of gear.

One can always argue "but its safer", and one can always counter with "how safe is safe enough?"...

..."Safe enough" is a personal decision.

-Z

Thanks, this clarifies the point. But still the number of hoses do not change...
The costs are higher (but not so much for me, I service them myself, I will never leave my regs in the hands of a technician of unknown skillness), and probably the benefit is not worth the additional costs. There are no drawbacks, indeed, it is just a matter of evaluating the ratio between costs and benefits.
At the end, thanks to all the contributions received, my decision is the following: I will service and set up just two first stages (one for me and one for my wife), each with the main second stage plus a secondary one (octopus). And I will mount the DIN kit on both, for reducing the risk of an O-ring failure (with with joke I have seen this happen several times).
Then I will prepare a third complete setup, identical to the first two, to be used as a backup if one of the two main systems fails.
So I will make good use of all my six 109-156, and I will employ the three first stages equipped with SPEC and 5-ports swivel.
I will leave the two other older first stages, unserviced, with yoke mount, in my collection of vintage equipment...

 

[Zef]

Thanks, this clarifies the point. But still the number of hoses do not change...

Just thought that through again and realized you are correct the number of hoses does not change.

You can think of it in the context of cost/benefit...or you can think of it in the context of what you and your wife would be most comfortable diving. There would be nothing wrong with selecting the configuration with two 1st stages, just as there is nothing inherently wrong with selecting to configure your gear with only one 1st stage.

Play around with it and settle with the configuration that is best suited for the type of diving you will be doing on any given day...

...not really any bad choices here.

-Z