Isolator Manifold, Fully open versus Partially open

[elmagnoon]

Hi UTDers,


I'm curios as to the thinking behind partially opening the isolator on a twins versus fully opening them. One argument is that having it fully open eliminates confusion in an emergency as to which way to turn it closed. In that case the diver must locate the failure and then decides to isolate.

The other argument follows the logic that the diver should first isolate (to at least save the gas in one tank) , locate the failure and shut down the post, then open the isolator. In that case it is recommended to keep the isolator only partially open as to make it faster to close.

At this time I'm leaning toward the second argument but interested in hearing what people think.

[JamesMottUTD]

Open your valves. A partially open valve will lead to confusion, turning it the wrong way and in the end is not going to save any time. Even backing your valves off a Ž½ or Ž¼ turn will play tricks on your mind underwater, while trying to solve an issue.
Shutting down and breathing down the right post still finding bubbles and then isolating is not going to take any more time than starting to close, and then starting to open and then closing all the way, opening back up all the way, then closing all the way again and thinking to yourself, ťid I just open or close that?
The only thing that is going to save you time underwater while dealing with a valve failure is proper training and practice. You must be able to manipulate your valves in a calm and calculated manner while still keeping awareness of your location in the water and the rest of your team. That will be the real time and gas saver.

[BDub]

What James said.

I'll add that isolating does nothing to solve the problem. Isolating is simply trying to "fix" a problem, when you don't even know what the problem is. Figure out the problem, then solve it. That may or may not mean isolating.

[elmagnoon]

Thanks for your replies. I greatly appreciate the input.

[stmichael]

I see another problem with partially open. If you are close to closed, you risk "roll off" in overhead env. Not a good thing.

[SeaCobra]

Would you ever dive with the isolator in the closed position? I ask this because there is a popular instructor in my region that is teaching his tech students tot dive with the isolator closed and to dive the rig as a set of independent doubles switching regs every 300-500 psi.

His thought is that in the event there is a need to close the isolator, it is already closed and you have minimized any gas loss. My feeling is that while that is true, many other problems have been created; gas planning, task loading, air sharing and risk of snd stage freeflow spring to mind. I am sure there are others.

Input, especially with any hard data, would be appreciated.

Jeff

[it_mike]

Would you ever dive with the isolator in the closed position? I ask this because there is a popular instructor in my region that is teaching his tech students tot dive with the isolator closed and to dive the rig as a set of independent doubles switching regs every 300-500 psi.

Only as practice for independents...if he's teaching doubles, and wanted to have his students prepared for both styles, isolator and independents, I could understand his direction.

[dbulmer]

SeaCobra,

I'd never dive with the isolator closed for 2 main reasons:-

1) Someone filling the cylinders may not have checked the isolator and assumed it was open.
Result: A lot less gas in your cylinders. If you spot the mistake then you might not have time to rectify the problem before your dive starts.


2) I want to ensure that the gas I'm breathing is correct ie one tank might contain an extremely high 02 percentage whereas the other might contain a low percentage of gas. If the diver has not been rigorous in analysing their gas before entering the water you might end up breathing 02 at depth. Avoid the problems in the first place by keeping the isolator open.

[AndyNZ]

Would you ever dive with the isolator in the closed position? I ask this because there is a popular instructor in my region that is teaching his tech students tot dive with the isolator closed and to dive the rig as a set of independent doubles switching regs every 300-500 psi.

There are some navies that dive "a bit" like this as an operational practice. I *think* the logic is based on not having/looking at the SPG - but don't quote me on it.

The practice is breath down the right post until the tank is empty, open the isolator to equalise pressure and then close. Breathe down the right post again until empty. You've now hit your gas reserve, open the isolator and end the dive.

Posted for people's curiousity only - not a recommendation for team diving practices!

[DaleC]

Would you ever dive with the isolator in the closed position? I ask this because there is a popular instructor in my region that is teaching his tech students tot dive with the isolator closed and to dive the rig as a set of independent doubles switching regs every 300-500 psi.

His thought is that in the event there is a need to close the isolator, it is already closed and you have minimized any gas loss. My feeling is that while that is true, many other problems have been created; gas planning, task loading, air sharing and risk of snd stage freeflow spring to mind. I am sure there are others.

Input, especially with any hard data, would be appreciated.

Jeff

This is an interesting question as I dive independant twins (solo) and when asked why I don't have a manifold I say (in that situation) I would dive with it closed anyways. However, respecting this as a UTD forum I assume the discussion should probably follow UTD SOP's based on team diving rationale.