Breathing down twin tanks while cave diving?

[slackercruster]

I talked with a few divers about cave diving techniques. One said that cave divers have to change regulators every few hundred PSI to breath down the redundant tanks in unison, implying the manifold is shut off all the time. Another said that cave divers breath out of only one regulator unless it is an emergency and the 2 tanks are connected with the manifold, unless there is a need to shut off one tank. If an emergency comes up the diver will reach back to turn the manifold valve to isolate the tanks?

Are they both right or is there a generally accepted technique when cave diving to manage the air in the 2 tanks?

Thanks

 

[Kim]

I'm guessing but I think you are describing the different techniques for independant doubles(no manifold), or manifolded doubles.

 

[slackercruster]

I'm guessing but I think you are describing the different techniques for independant doubles(no manifold), or manifolded doubles.

Maybe independent? The one diver did not mention whether independent or not? I thought all cave divers used manifolds though?

 

[Kim]

Maybe independent? The one diver did not mention whether independent or not? I thought all cave divers used manifolds though?

Not if you are diving sidemount for sure. You wouldn't want to breath one tank all the way down, then switch over and find that you have a major problem with the tank that now has your only air.

 

[mart1]

I talked with a few divers about cave diving techniques. One said that cave divers have to change regulators every few hundred PSI to breath down the redundant tanks in unison, implying the manifold is shut off all the time. Another said that cave divers breath out of only one regulator unless it is an emergency and the 2 tanks are connected with the manifold, unless there is a need to shut off one tank. If an emergency comes up the diver will reach back to turn the manifold valve to isolate the tanks?

Are they both right or is there a generally accepted technique when cave diving to manage the air in the 2 tanks?

Thanks

Cave divers use different setups: doubles with manifolds, or independent doubles (most often in the form of side mount today)
With doubles you breathe from one regulator, and in case of air loss you try to isolate the problem by either shutting off the regulator with the problem or closing the isolator valve thereby saving half your air supply. Depends on the problem.
With independent doubles you change regulators every few hundred psi, so you won't be out of air if one tank is nearly empty and the other develops a problem.
Either way you reserve two thirds of your total air supply to get out of the cave.
And then there is stage diving, where you take extra tank(s) to get you further into the cave. These are always used first, most divers use them for one third and then leave them behind to be picked up on the way out. There are some divers who use a stage tank for one half, reasoning there will never be a major air loss on more than one tank.

maarten

 

[cerich]

99.9% of cave divers today are diving an isolation manifold and using one reg to breath from both tanks.

Side mounting where independant doubles are needed is actually not that common and very few (and they are very experienced and dedicated cave divers that do) cave divers do this.

 

[mart1]

99.9% of cave divers today are diving an isolation manifold and using one reg to breath from both tanks.

Side mounting where independant doubles are needed is actually not that common and very few (and they are very experienced and dedicated cave divers that do) cave divers do this.

I guess a lot depends on where you dive. My experience is different.

 

[MikeFerrara]

These days you'll see lots of sidemount divers at just about any popular Florida cave not to even mention all the caves that require sidemount.

 

[cerich]

Hey guys, you wouldn't say that the vast majority of cave divers you see are of the "follow the gold line" variety? It seems that way to me.

 

[MikeFerrara]

Hey guys, you wouldn't say that the vast majority of cave divers you see are of the "follow the gold line" variety? It seems that way to me.

I'd agree with that statement but I'd also point out that more and more of them are diving sidemount whether they need to or not. I'd even agree that backmounted doubles divers are in the majority but I don't know that I'd saya "vast" majority. Even if you could use that term, sidemount isn't at all rare. If you spend a few hours at P1 on a weekend I think you'll see quit a few.

Of my own freinds that cave dive about 1/4 dive sidemount almost exclusively and most of us have sidemount rigs even though we prefer manifolded doubles.