Why recreational backmount doubles

[Wibble]

Could you convert that into American for me please? (Is that 2 bottles X 7 liters each at 300 BAR?) They do look nice!

Easy. That's two 246 fluid ounce tanks filled to 300 atmospheres.

However, the gas volume is simply the wet volume (7 litres) multiplied by the pressure (300) equals the atmospheric pressure gas: 7 x 300 = 2100 litres = 76 cubic feet. What that is in the insane US system is anyone's guess.

Oh, and no smarty pants comments about that being an approximation due to gas compression rules. Your SAC isn't constant either.

Although... it's hard to get a full 300bar/4351.132psi fill. Seem to mainly get about 270bar/3916.019psi which then reduces the volume from 7x300 to 7x270=1890 litres/66cuft. Which is why 12 litre 232 bar tins are easier for volume and filling.

 

[Gone for diving]

Seems better than lp50s unless you really overfill them.... some guys have told me they fill them to 3600psi...

 

[Couv]

What that is in the insane US system is anyone's guess.

...basically a cubic foot less than an AL80 divided into two tanks-but still very cute.

 

[broncobowsher]

...basically a cubic foot less than an AL80 divided into two tanks-but still very cute.

and about 50% more pressure

 

[OrcasC205]

...basically a cubic foot less than an AL80 divided into two tanks-but still very cute.

I think that was 76 cuft per cylinder, so like double AL80s.

 

[Couv]

Oh, so twice the amount of air-and about 3 times as seductive.

 

[plaamook]

Well as no one's mentioned it/them...
Anyone dive or have dived independent twins?
Indis mean you obvs have to change your reg and manage your air in a different way but I've found it makes for a very flexible set up. At least for most of the fun diving I do.
Its easier to get two single tanks in and out of or up and down things. On a dive trip dive boat you don't need special twins you just twin up the rental tanks or what have you. No concerns about damaging manifolds.
I love it.
I'm partial to my old commando BC (still...) which is v easy to change from single to twin config so I can switch between single/pony for shallow stuff or twins.

But in answer to the op's question...I only really dive solo for fun and I've found that after you get used to being really self contained...I just can't really deal with some other diver having my spare air thanks very much. Even if I'm diving with another human.
So that is why I dive twins.

 

[rx7diver]

Well as no one's mentioned it/them...
Anyone dive or have dived independent twins?

My preferred way of diving doubles solo.

rx7diver

 

[PfcAJ]

Independent doubles - the worst parts of backmount mixed with the worst parts of sidemount.

 

[broncobowsher]

Independent doubles - the worst parts of backmount mixed with the worst parts of sidemount.

That's how I think of it as well. A solution to a problem that was created specifically for that solution. Can we add a Z-manifold as well, to fix the problems created by the solution?