Independent Doubles vs. Isolated Doubles

[sunkarm]

Some cave divers prefer independent citing issues like reduced snag hazard etc. In theory as theyre 2 totally separate systems something like a manifold failiure cannot possibly lose all your gas (that said a failiure on independent means you will lose half your gas).

Cost is the main issue i use them - can use 2 normal tanks without the expense of dedicating tanks to twins, buying manifolds, backplates etc. Very easy config to swap between single and twin tank use (just the case of changing a cam strap and takes 2 mins).

which BC did u use?

thx

 

[GrandpaScuba]

You might ask this question in the Tech forum.

 

[String]

Rather old thread but i used at the time a Buddy Tekwing with independents and singles.

 

[plclark196]

If cost is your main issue then you might want to re-evaluate your priorities.

Independent Doubles:
two normal tanks put together in a band system.
You will have extra task loading of breathing down the tanks evenly.
If you a regulator goes bad or lose an o-ring on your tank then you lose half your gas supply.

Manifolded Doubles:
If you lose a regulator then you turn that post off, but still have access to the gas supply in both tanks.
You don't have the task loading of breathing down the tanks evenly.
Aren't as readily available at dive resorts (for now anyways)

How much gas is lost while shutting down a post valve with manifolded doubles???-assuming a HP failure??? .....just wondering...........

 

[Nemrod]

which BC did u use?

thx

I still have my independent doubles I used for caving from the early 70s until I met she who rules my life who said NO to any further cave diving. I had LP 72s I still have and LP 108s. A central mounted third smaller bottle or canister for my cave light which was a 50watt aircraft landing light and powered by NiCds from a turbine starting battery. The BC I came to prefer is this dual bladder Dacor SeaChute. The lower bladder in black was the primary bouyancy bladder, the upper bladder with a full size dump could be orally inflated in an emergency for secondary bouyancy control should the lower bladder fail--it never did. The power inflator you might notice is located at the lower bag. This BC provided excellent horizontal trim and had a large and useful pocket.

She who rules my life is shown here modeling the BC while diving an interior lake sometime around 1980 give or take--no doubles though. She decided it was HERS because it matched her mask and her shortie that was blue with an orange stripe. So, I did without.

N

 

[Soggy]

How much gas is lost while shutting down a post valve with manifolded doubles???-assuming a HP failure??? .....just wondering...........

It depends on how deep you are, what the failure is, and how quickly you react. Joel Silverstein did an experiment on this and published it in ADM, I believe. LP failures are actually much more devastating than HP failures.

 

[ArcticDiver]

How much gas is lost while shutting down a post valve with manifolded doubles???-assuming a HP failure??? .....just wondering...........

Depends on the factors mentioned plus the how the diver is doing that day. On a day when I'm cold, tired, am doing the first of my dives after not being in the water for 4 months and with minumum air in my dry suit; quite a bit. On the other hand if I'm "on my game" negligible.

 

[plclark196]

It depends on how deep you are, what the failure is, and how quickly you react. Joel Silverstein did an experiment on this and published it in ADM, I believe. LP failures are actually much more devastating than HP failures.

Why is a LP failure more devastating than a HP failure...? Also, seems to me that the worst failure would be a neck O ring or a burst disk (both of course are HP)...neither of which I can shut down with a post valve - so back to one of the benefits of independant doubles.

 

[ianr33]

Why is a LP failure more devastating than a HP failure...? Also, seems to me that the worst failure would be a neck O ring or a burst disk (both of course are HP)...neither of which I can shut down with a post valve - so back to one of the benefits of independant doubles.

A HP HOSE failure will only result in a slow leak as the gas will be coming out of a pinhole restriction in the reg. Would take around 20 minutes to empty an 80 from full.

A neck O ring or burst disc failure can empty a tank in 90 seconds or so,roughly the same as a LP hose failure.

 

[Nemrod]

When we really counted on the air in our tanks we realy removed the burst discs from the valves. Neck O rings do extrude but if you are cave diving you are not depending on a 30 yo O ring.

As to LP hoses vs HP hoses scubatoys has or at least had an excellent and funny little video clip demonstrating the difference. N