independent doubles

[jeangadbois]

If this is not in the right place please fell free to move it.

I have recently started diving independant doubles . I am doing so while i save and slowley buy a bigger set of manafolded doubles. I am using a 45lb wing with 2 al 80's at the moment.

My question is are there any risks or added concerns i should be made aware of that were not present diving a single tank.

Thanks in advance for the help.

 

[tbone1004]

well spelling everything properly would be a start. I am assuming by your name that you are from the French section of the great white north, but using proper spelling helps with the search function for new divers as well as the forums software for matching "similar threads"

independent
manifold

other than that, not really. You can buy a manifold pretty inexpensively if you want to go that route, but making sure you are balancing the air pressure in the tanks is important, having an SPG on each tank obviously, and understanding that you can't always donate the hose in your mouth all the time so your long hose has to be on a quick breakaway *quite often an o-ring*, for donation

 

[Kevrumbo]

Gas consumption monitoring and balancing out the trim of your bottom mix tanks by alternating breathing off each cylinder (either by switching regulators in classic backmount/sidemount independent doubles technique; or by alternately turning on one tank valve & shutting down the other as in UTD Z-system Sidemount configuration) will take some practice getting used to the methodology. For example, when I dive Z-system Sidemount with AL80's (11L/bar) cylinders at full 200 bar initial pressure for a dive to 45m:

I typically start on descent with the Right Tank On/Left Tank Off for a delta of 40bar down on the Right Tank (160bar total remaining pressure Right Tank) over an approx 4 to 7min time period depending on depth & workload. Switch to Left Tank On/Right Tank off and delta down 70bar on the Left Tank (130bar total remaining Left Tank) over a 5 to 8min period again depending on working depth & workload; switch back to Right Tank On/Left Tank Off and delta 70bar (90bar total remaining now in Right Tank) for another 5-8min period; and finally conclude bottom time switching back to Left Tank On/Right Tank Off & delta 70bar (60bar total remaining now in Left Tank) as I start ascent on my deco profile. On deeper/longer bottom depths & times, I may switch back to the Right Tank one last time before switching to my 50% deco bottle gas at 21m. . .

 

[tbone1004]

why in the hell would anyone depressurize the regulator in independent doubles? Only reason UTD does it because the manifold system can't balance the cylinders out and because the block is on your back you can't have a valve that you move to either side to switch which tank you are breathing off of.

To the OP, anyone who chooses to turn the tank valve off when not breathing on that bottle in a standard sidemount or ID situation is a bloody idiot. Anyone who recommends it clearly hasn't thought of the ramifications of those actions *if diving a drysuit you lose either the ability to inflate your suit, or your BCD depending on which bottle you are on.

gas logic, just read the milliondy thousand threads on here about sidemount gas management and you'll figure it out. For OW diving there is no "right" way to do it. With AL's it is probably easiest to breathe down to 150bar from wherever your fill pressure is then switch every 50 bar from then on out. 80's are small enough that 50bar is only 1.5lbs so shouldn't be an issue. If you don't like that, then switch every 20bar but that is a bit excessive imho

 

[jeangadbois]

Forgot to mention i have bin switching about every 500 psi and i do have an spg on each tank

 

[Kevrumbo]

why in the hell would anyone depressurize the regulator in independent doubles? Only reason UTD does it because the manifold system can't balance the cylinders out and because the block is on your back you can't have a valve that you move to either side to switch which tank you are breathing off of.

To the OP, anyone who chooses to turn the tank valve off when not breathing on that bottle in a standard sidemount or ID situation is a bloody idiot. Anyone who recommends it clearly hasn't thought of the ramifications of those actions *if diving a drysuit you lose either the ability to inflate your suit, or your BCD depending on which bottle you are on.

gas logic, just read the milliondy thousand threads on here about sidemount gas management and you'll figure it out. For OW diving there is no "right" way to do it. With AL's it is probably easiest to breathe down to 150bar from wherever your fill pressure is then switch every 50 bar from then on out. 80's are small enough that 50bar is only 1.5lbs so shouldn't be an issue. If you don't like that, then switch every 20bar but that is a bit excessive imho

Clarification for you sir . . .one does NOT lose the ability to inflate a drysuit & wing using a properly configured UTD Z-System Sidemount with D-block or Z-isofold and as trained in normal operation.

 

[tbone1004]

you didn't clarify anything, I'm aware how the z-block works, I've used it, but this is independent doubles, not sidemount. Z-block is not pertinent to this discussion as it can't be rigged properly with bottles on your back or with a proper backplate. Read the original post or hell even the title of the post and you wouldn't have even mentioned the z-block

 

[rhwestfall]

its $100 for an isolation manifold from DGX....................

 

[jeangadbois]

Yep knew that just wondwring about independent doubles at the moment if theres something ive over looked

 

[Nemrod]

Yes, plan your dives and alternate tanks per the plan such that you always have enough air/gas in either tank to abort the dive to a point of safety also planned in the dive.

Do not shut the valves off when alternating source.

N