isolator open or closed?

[J1M1]

i only cose the isolator if i can not determine which side the failure is on, otherwise it never closes. If you have a freeze up or 1st stage problem on the reg that you are breathing, just switch to your backup and begin shutting down the TANK with the problem not the isolator. If i cannot determine which tank it is coming from , that is the only time i will close the isolator, followed by the problem tank. Since i dive in the thirds rule, thge only way i may o9se precious gas is if the problem happened while i was at the end of my dive r on a deep stop on back mix. I also agree with Dennis, who i believe has a very good understanding of valve shutdowns.

 

[scubafanatic]

Hi dennisgrimm,

.....I certainly have no problem with you playing 'devil's advocate' , so in the spirit of the original point of the thread, I do have to take issue with 'fleeing' from an OOA diver, and then, if forced, donating your octo and not your primary 2nd stage.

Most of the time you're gonna get 'mugged' for your primary, not politely asked for it...you'll never see it coming, (so you won't get the chance to 'back away') it will be gone before you're even aware there's an emergency. 'Tech' divers 'admit' this reality, thus configuring their gear/training for this most probable of outcomes......might as well accept this scenario as inevitable, and be ready with a donatable primary on a 7' hose...so when it happens it will be second nature to you.

Imagine you're confronted with poor vis (siltout/night dive/light failure in cave) and need to share air.....your OOA buddy isn't gonna waste time in total darkness figuring out where you happened to stash your octo......he's gonna find your body, figure out where your head is, then find your mouth area and grab the reg...'cause human anatomy is predictable...gear 'stowage' is variable, people stuff/stash octos all over the place, they're not gonna drown wasting time sorting that out.

Once your buddy has the long hose, you switch to your necklaced octo...which is REAL close by you, and you're good to go.....remember, you'll be out of air a few seconds at most while making the switch.......your buddy has been OOA for god knows how long, a few more seconds could make-or-break him, make it as easy/obvious as possible for him.

As for the manifold question....for the most part I doubt you'll be allowed by a technical instructor to dive the manifold 'closed'...not if you want the certifications...however, I suppose on your own you can do whatever you wish. I've been taught to either leave it all the way open or to leave it a little bit open so it only takes a turn or two to close...personally I prefer to dive with it all the way open, that way in an emergency I won't get confused which way is off......if the manifold knob is left in an 'intermediate' half-on-half-off position it's possible to get confused which way is 'off'...I like it all the way 'on', that way I know the only direction it's possible for it to move is 'off'.

Karl

 

[DA Aquamaster]

i only cose the isolator if i can not determine which side the failure is on, otherwise it never closes. If you have a freeze up or 1st stage problem on the reg that you are breathing, just switch to your backup and begin shutting down the TANK with the problem not the isolator.[/ QUOTE]

I think you mean REG rather than TANK. The valve shuts off flow to the free flowing reg, but tthe air in the tank is still available through the manifold as long as the isolator valve is open.

That is the advantage of an isolator manifold over independent doubles, where if you shut off the the reg, you are in fact shutting off the tank and losing access to that air. No big deal if the reg froze up as it will thaw in a few minutes and you can turn it back on. But is a more permanent issue with a mechanical failure and the reason that you breathe a third out of each independent double during the dive to ensure either tank has enough air to get you safely back to the surface from any point in the dive.

 

[J1M1]

Correct, which is why i believe the isolator should never be closed. Also if you have a tendancy to switch the isolator on and off between dives, you may forget at depth that it is off, run out of gas in the primary tank and forget about the other tank. I know people have died in this situation...

 

[Walter]

Seems like a moot point to me. Wouldn't it make more sense to be shutting down the valve with the problem than screwing with the isolator. If you shut down the valve, but leave the isolator open, you save more air and you still have access to all that wasn't lost. If you shut down the isolator first, you continue to lose air even after it's closed. The isolator is only useful if you lose the o-ring at the tank/valve interface or a burst disk. I've never heard of either of those happening on a dive. It'll much more likely be a free flowing regulator or an o-ring at the valve/regulator interface that causes you problems. The isolator is useless in that situation and causes more of a problem if you reach for the isolator instead of turning off the valve.

 

[Michael Schlink]

I am fairly new to this board, but you guys are a hoot. I'm thinking about buying everybody a ticket somwhere we can all go diving together. Now her's my version. It's already been said but I'll add a little real world. Isolator is open all the way so I can only turn it one way and I have practiced so I can shut it quickly, no problem and I am going to continue to practice so that I remain profecient(sic) Now for dennisgrimm 's choice for reg config. Back when I did my cave training (about 16 years ago) It was not uncommon to see the long hose bungeed on the tanks and some of you may remember seeing books with it bungeed across the manifolds right behind your head. I actually did this a few times. I would agree with the notion of not handing off your perfectly working reg and just handing the OOD your alt but like scubafanatic said you probably aren't going to know when your buddy 's coming for it, it sure would be nice to get a heads up so to speak but the OOD might be a little preoccupied with not dying and skip the signal. Now for a real happening and not a scenario. I had completed a dive and was hanging in the cavern opening resting, this was about 14 years ago, A cave instructor I know had a student that need to do his OOA drills I was asked to be a donor. I dropped inside the cavern and waited for the student to approach. Without warning my primary got ripped outof my mouth. I watched as the student frantically shoved my reg into his piehole and started draining my tanks. I picked up my alt and between laughing and crying because my teeth hurt I signaled to the diver OK and go up. We surfaced, I passed the student back to the instructor whome I'm quite sure spent the afternoon working on OOA drills with his student. Point is this The OOD is going for your primary like it or not and he's going to get it if he gets his hands on it. LET HIM have it, he damn sure needs it more than you do. Then go for your alt. and everybody's happy. I personally think that the long hose wraps around and you breathe it until sombody needs it. Alt goes on a necklace and I now have that shortened so that I can pick it up no handed. chin down bite mouth piece breathe air. Also probably 15 years ago this was being kicked around alot I think because Scubapro was pushing their air 2 any way somebody did a study of some sort and determined that handing off the primary was way faster than any other way of deploying/sharing a reg. So dennisgrimm. If we are diving togther someday and I need to share are with you please don't swim away and if I can I'll try to let you know that i'm drowning and would appreciate a little air donation. P.S. I used to use the old style mouthpiece with the little moldeable bite tabs but when someone ripss the reg out of your mouth it hurts- dive safe- You guys talk nice play nice, O.K.