Diving with redundancy.

[Nemrod]

Nemrod, I agree with you, but you are answering a question different from the one of the OP. He did not ask about using two regs on the same single cylinder, he just asked if getting a cylinder with an H valve is a good idea.
It is not the same question.
You assumed that the second post will be used for a second reg.
This happens very rarely in my experience.
Here in Italy most rental cylinders are 15 liters with double valve (H or Y). I would never rent a cylinder with just a single post, as this is less reliable.
Then I dive with a single first stage, with DIN attachment, which is perfectly fine for rec diving.
So my answer to the original post is: yes, a cylinder with an H valve is a valuable asset, as it allows you to go on if one of the valves has a problem, mounting your reg on the other post.
I am not the only one thinking this way. In fact, most cylinders here are with two valves, exactly as the users like them...

The OP indeed wanted to use twin regulators as there really is no other purpose for Y/H valves that I can see so therefore of course I made that assumption. Most recreational divers who rent tanks in the North American including the Caribbean and Mexico will be getting a single post tank and it will likely be with a yoke valve, not DIN. Certainly there are stores that rent DIN but I do not recall seeing many/any Y/H valve for rental. Most divers in North America who do local diving own their own equipment including cylinders. Curious, but probably off topic, how is a Y/H valve more robust than a single post valve if installing a single regulator? I recall that you have had several regulators occluded with FOD. If the cylinders are so filthy that they cannot be relied upon with a single post/dip tube valve I do not think the answer is a Y/H valve.

It is a true consideration that the ABC agencies do not teach adequate air management to open water divers. For most, with less than good SAC, the dive would be at end before they reached the objective if considering the need to supply sufficient air for two divers to return to the surface with safety stop. I just love seeing open water divers on the Spiegel with a single 80. It works, they usually make it back to the platform with 500 psi give or take, but if they had an issue and needed to actually bail to their buddy, well, it would be tight!

Regarding a pony or what I prefer to call an auxiliary bottle, if slung, 19 to 30 cf, I never really notice it in the water, but twins, oh yeah, I notice that, especially coming up the ladder. I am getting old, lol. I can unclip the pony and hand it up if I am tired. I only rig for a auxiliary bottle if I am solo diving. My wife and I do practice the buddy system.

James

 

[Angelo Farina]

Yeah, I know that on the other side of the ocean the typical tank is just 11 liters, single post, yoke only, while here it is 15 liters, dual post, DIN+yoke...
Different approaches, different diving profiles, different average depths.
And different equipment: all tanks here are dual use, they mount DIN, but, screwing in a nut adaptor, they can also be used with old yoke regs...
We think that our tanks are safer, with their larger size, dual post and DIN.
Americans think that EU tanks are not safe, as there is no burst disc.

 

[Jcp2]

What is the air source for a diver with a y valve problem while they are moving the first stage from one side to the other?

 

[Angelo Farina]

What is the air source for a diver with a y valve problem while they are moving the first stage from one side to the other?

Usually you break one of the valves on the boat or on the land, when the cylinder falls being mishandled. So you are breathing normally, not from a reg...
I never suggested to change post underwater!

 

[MichaelMc]

Usually you break one of the valves on the boat or on the land, when the cylinder falls being mishandled. So you are breathing normally, not from a reg...

So to be clear, with the more reliable reg to valve connection of a DIN, you are not talking about Y valve for underwater redundancy. You are talking about redundancy gearing up on land/boat, that that tank actually has a functioning valve/post that you can use. Because maintenance or handling may have been spotty.

 

[lermontov]

You know, my wife has told me for 38 years that if I did not have a job and take out the trash, I would be completely redundant. Or superfluous. So, every time I dive, I am diving with redundancy.

sounds like she has a lover too!

 

[Angelo Farina]

So to be clear, with the more reliable reg to valve connection of a DIN, you are not talking about Y valve for underwater redundancy. You are talking about redundancy gearing up on land/boat, that that tank actually has a functioning valve/post that you can use. Because maintenance or handling may have been spotty.

Exactly. Before switching to DIN, I was using two complete regs with yoke mount.
Initially on twins (which were the standard here until 1980), and then on singles.
DIN started to be the norm around year 2000, and nowadays if you still have a reg with yoke you look like a dinosaur. However, the cylinder can still use it, installing the nut adpator.
After switching to DIN, I am using just one first stage, mounted on one of the two available posts.
But I still always rent tanks with two posts! Why should I ask for one with just one post? Which indeed is quite rare here, at least on a 15-liters cylinder.
Instead they are common on smaller bailout/pony tanks, where of course only one reg can be mounted.

 

[MichaelMc]

Exactly. Before switching to DIN, I was using two complete regs with yoke mount.
Initially on twins (which were the standard here until 1980), and then on singles.
DIN started to be the norm around year 2000, and nowadays if you still have a reg with yoke you look like a dinosaur. However, the cylinder can still use it, installing the nut adpator.
After switching to DIN, I am using just one first stage, mounted on one of the two available posts.
But I still always rent tanks with two posts! Why should I ask for one with just one post? Which indeed is quite rare here, at least on a 15-liters cylinder.
Instead they are common on smaller bailout/pony tanks, where of course only one reg can be mounted.

Ok. Most people likely don't put that under 'diving with redundancy', more like 'having backup gear in the car/boat' in case something breaks while gearing up.

If it is pretty common for any one valve to not work when gearing up, sure, having two per tank gives you twice the shot of getting one to work. If maintenance doesn't just devolve to only having one working.... If the tanks are handled like bowling pins loading in the boat, leaving the shop with two valves/posts might make sure you still have one when you gear up on the boat. But it seems that way you are diving a tank that already took a disabling hit to one of its two posts/valves.

My expectation is that a tank's (sole) valve will be properly functioning, or it is fixed or swapped for a different tank. For yoke, spare o-rings seem easier to carry than equipping everything with two posts. Once tank to reg connection(s) seem secure, then comes the topic of redundancy in the water.

 

[Nemrod]

Again, if you are having such issues with reliability with your DIN valves that you need a Y/H valve to hopefully get one to thread in you might want to consider joining us dinosaurs and use a good, reliable yoke valve instead of these seemingly unreliable DIN things. BTW, Dinosauria were quite successful and they are still flapping around today messing on my freshly washed Jeep. N

 

[NAM001]

I Use a H valve , I can use the same regs that I use when diving doubles and works great for dry suit air also.