isolator open or closed?

[DeepScuba]

To me it's too easy.

Since accidents almost NEVER happen, lets keep it simple. Breathe from one reg, all the time.

END OF STORY.

Why dink with, on every dive, checking 2 SPG's, switching regs appropriately, blah blah blah, when odds are 99.999999% all I will ever do, my whole life, is simply breathe off of one reg, check one SPG (If I even have to check it at all (Yes I do, but I don't have to, to know what the pressure will read)), and never have to worry about swapping regs, worry about anohter dangling SPG and hose, for no reason?

It's simply a smart way to dive since the odds of doing it any other way (IE having a problem) are very remote?

As for the amount of gas you have........you have what you have, and worrying about it won't save you one bit. You already should know if you have enough anyways. The dive plan was planned for a reason.

As Lane mentioned, the odds of having to KEEP your isolator closed (If infact you didn't know WHAT was leaking, so you isolate to conserve first), if then, you find out it's, say, your left post (1st stage), you can then shut it and re-open the isolator.

Do you have enough gas then???

Without a doubt, SPG or no SPG. You're just worried because now you can't read one.

P.S. A buddy to help see what's leaking also helps too. That's a drill my wife and I do every dive. (Bubble check).

You think you're one step ahead, when in fact you're adding, on EVERY DIVE, more steps (Reg switching and/or isolator opening/closing) depending on the style you're using. I will only touch my stuff IF I have a problem, which is basically never.

The odds always favor the "typical" dive. (Typical being a normal one with no problems).

 

[Boogie711]

Why?

This can't make it easy to deploy, or more importantly, restow, can it????

Which means you're not practising OOA emergencies near as often as you should be. Furthermore, it's out of reach, and could easily be an entanglement hazard.

I'm curious which agency taught you to bungee a long hose backup to a tank?

 

[Diver0001]

DeepScuba once bubbled...
Rotuner:

Can you imagine being in 1/2 a tank, and then as you're busy screwing needlessly around with valves, the one than was full just blew!!!!

Now you're down right to the wire immediately. No gas reserve anymore at all, for you, never mind your buddy. Sure, open that valve to let in some high pressure until the leaking tank matches the one you need and then shut it quick!!! cause now it's in reverse!!

Seems like a complete waste of time screwing with valves when you should be diving. All you need is a minor mental lapse to create confusion where none should have been in the first place.

I can't defend it. I'm only saying that I've heard this. Personally I'm in the leave it open camp.

Maybe this technique comes from the days before SPG's. That would be the only compelling reason I can think of..... Without an SPG it would give you a good idea of how much gas you still have.

And although I appreciate the point you're making, I also think the chances of a tank "just blowing" at the very moment you're screwing with the valve are about the same as your chances of getting beamed up by aliens who want to have sex with you. YMMV

R..

 

[dennisgrimm]

Boogie:
My octo is bungeed to my left tank. By that I mean that I have a bungee cord around the tank and the majority of the 7ft hose is tucked under it. The second stage comes over my left shoulder and is held in place. It is very easy to reach. I just reach with my left hand a little past my inflator and it is right there. I donate it holding the hose. As I donate it it pulls free of the bungee and is clear. It is easy to stuff back into the bungee. Everytime I have practiced an OOA situation my buddy always restuffs it for me. I can not restuff it myself underwater and if my buddy won't put it back I can always wrap it around my neck DIR style, but I avoid this because I find that it clutters everything (IMHO). I like it because it is accessable from in front of me and behind and my buddy can grab it without getting my attention first. You can actually find a pic of this type of octo setup in one of the DIR books (I can't remember which) as an example of what not to do. I can not recall the exact wording, but the explanation of why it is the wrong thing to do didn't exactly convince me. I humbly disagree with the DIR donating the primary thing. Personally, if someone needs air and reaches for the reg in my mouth I am going to swim backwards away from them and hand them my octo. If they are panicked, the last thing I need is to have no reg in my mouth (even if it is for a second). I have read the DIR-F book and understand why the DIR guys do what they do it. That is what ANDI and my LDS teach.

All of that said... I am rethinking my gear setup and may start diving with an open isolator, one SPG, breathing from the long hose and donating it in an emergency :wacko:. That is the whole reason I started this thread, I need some convincing. I will be giving it a try to see what I think. I will have to rethink the way I do things and the above explaination of why I have a bungeed octo would no longer be relevant. The good news is that I wouldn't need to buy any more gear.

 

[dennisgrimm]

re-reading that last post it looks like a contradiction. I was just trying to explain what I currently do and why. Also, I am considering changing my setup.

 

[Don Burke]

dennisgrimm once bubbled... Don:
1. I don't see how shutting the isolator fixes the leaking gas. Just for the sake of discussion, if you and I were to have the exact same problem at the exact same time. First, you would be closing your isolator and I would be looking at my SPG's (if it weren't obvoius which tank were leaking in which case I would be shutting down the leaking tank). Next, you would be looking at your SPG to figure out which tank was leaking (if it weren't obvious) and I would be closing the offending tank. Lastly, I have begun my ascent and you are closing the offending tank. See how I am one step ahead the whole time? This was a theoretical situation. Maybe you are faster than me, maybe lots of things. The point is, there is one less thing to do in that emergency situation. I would gladly trade having to constantly monitor 2 SPG's in exchange for having to do one more thing in an emergency.

Shutting the isolator protects a portion of your gas. Getting the rig back to the shop is going to fix it. By the time you have looked at your SPGs, I'll have the isolator shut and will be looking for the source of the bubbles to tell me which valve to shut next. By the time you have figured out what those two SPGs are telling you, I've already isolated the offending post and I am ascending.

I probably won't look at my SPG until I'm at a deco stop. It won't help me, but then I have time to kill and need something to do.

dennisgrimm once bubbled... 2. Obviously, the dive would be thumbed. The amount of gas you have woud be a big factor in deciding what to do... wouldn't it? If you have just a couple hundred PSI left wouldn't you make for the surface instead of your first deco stop?.

If I shut my isolator first, I'm going to have quite a bit of gas left, so I'll at least get my first stop done. I wouldn't make for the surface until every option had been exhausted. My buddy has backgas, we both have deco gas. There are other divers around with gas. _Something_ ought to get me out of this without a chamber ride. If I flatten the backgas with no other options, I'll change the plan, but not until then.

dennisgrimm once bubbled...
3. I know... ya lost me on this one. ???

If for some reason, a tank has failed, I've lost the use of the first stage on that side anyway, so shutting the isolator doesn't cost me anything.

 

[theskull]

1. Yes, the transmitter on the right post IS a second SPG. It is also more a matter of convenience than a redundant system. The Vytec transmitter fails every time a gas shutdown is practiced (or needed!) anyway, and occasionally fails for no apparent reason. I like the convenience of my air pressure on my wrist with my depth, time, and deco info.

2. Yes again, to Dennis, who correctly surmised why I dive with a partially closed isolator valve--can be totally closed with 2 quick twists yet still equalizes the tanks.

3. As many have said, after a failure your actual pressure is inconsequential since the dive is over, you are exiting with more than 1/3 gas unless your failure happened at max penetration, and you are with your buddy/team--who KNOW that you have had a problem and may need some of their ample supply of reserve gas.

4. The military technique that was referenced is for diving in zero viz when you CANNOT see your SPG. If for example you begin with 200 cu ft of gas and breathe 1 tank to empty (empty! how would you know 1/2 empty with no gauge or no viz?), then you open the isolator and know that you now have 100 cu ft. Repeat once more, and now you know you have 50 cu ft. for your ascent.

5. Dennis, the fact that all answers so far favor an open isolator and breathing from the long hose do not mean that your method is wrong. Your instructor and dive buddies need to be consulted before you make a change while diving with them. But the standard practices are usually standard for a reason--give this some thought. Also, if your "safe second" is bungied around your neck and you have often practiced sharing air, then giving up your reg to an OOG diver is not at all a problem--certainly it is less complicated than the isolator equalizing manipulations and diving with unequally weighted tanks you are currently practicing.

Congratulations on questioning what you are doing and inquiring as to whether there is a better, easier, or more logical way; we should all be doing this very often!

theskull

 

[RichLockyer]

In the case of a 2nd stage freeflow, you will always know which side to shut down IF you always have the isolator open.
If the reg in your mouth is freeflowing, shut down the right post and go to your backup reg.
Likewise, if the reg under your chin (or on your shoulder) is freeflowing, shut down the left post.

In both cases, you have have access to 100% of your gas and didn't have to touch the isolator. Whether the SPG is on the functioning post is irrelevant, as the dive is over. I'll touch on the deco issue later.

In the case of a 1st stage freeflow, it will most likely manifest itself in the form of a 2nd stage freeflow, provided you are diving a downstream reg. Follow above procedure.

If diving an upstream reg, then you probably have an OPV on the 1st stage, which means that the bubbles will be coming from behind your head.
You will be able to tell which side by listening. If you are deaf in one ear as I am, a quick roll onto your back will probably tell you, but the best move is to go to your backup and shut down the right post. Bubbles still there? NOW shut down the isolator... you still don't know if it's a neck o-ring, manifold, or a reg failure.
Reopen the right post, shut down the left. If the bubbles are still going, then you have lost a neck o-ring, manifold, or burst disk. Your buddy can tell you which side... you can then either go to the OTHER 2nd stage and ascend.

Why isolate nearly last? The neck o-ring is the least likely item to fail. It can and DOES happen, so you need to be able to handle it, but it is the least likely of all failure modes. You are more likely to lose a reg or a hose, and a blown o-ring, manifold, or burst disc are the only failures that require isolation.

Why the right post first? If it's a reg freeflow/freezeup, it is more likely that the reg you are breathing on will go. Your primary and your wing are both on that left post. All your backup reg is doing is feeding the SPG, and maybe the suit if you're on air/nitrox.

One situation where I may isolate first would be if I have just contacted the overhead HARD and I'm worried that I may have damaged my manifold. After a hit, the most likely failure mode is no longer a reg or hose (assuming that regs and hoses are routed so as to protect them).

On the deco issue... if you are encountering serious decompression time, it could be argued that you should be doing it on nitrox, even adding O2, thus, you would still have all of the gas that you need for the required shallow stops. EAN50 is good at 70ft. If you have stops deeper than 70ft, then you most certainly will not be doing 100% of your deco on your backgas, so, following the rule of 3rds, having to isolate out on exit at the 1/3rd point, leaving you with 1/6, will give you enough to ascend to safety.

 

[dennisgrimm]

Rich:
WOW, that is a lot of info and I need to digest it, but it all makes sense. That is going to take time to master.

TheSkull:
I like the way you have your isolator open but mostly closed. That is a good idea. Thank you for the info about diving with no vis, it makes sense as well.

Don:
The more I read the more I feel that diving with the isolator open is the best way to be. However, I will play the devil's advocate and continue to argue my previous philosophy to play it out.

Setting aside you and me (becuase you are almost certainly a better diver) and holding everything constant except for the divers configuration... In the scenario where I proposed two divers having the same problem the diver that dove with his isolator closed would already be isolated and the diver with the open isolator would first have to close his. This means that the diver that dove with his isolator closed would go straight to "looking for the source of the bubbles to tell" him which valve to shut while the diver with the open isolator is closing his. One less step. That was my only point. The downside is the greater task loading for every single dive (as pointed out by others), the need for extra equpment, and possible confusion in an emergency about which tank you are breathing off of when diving independants. In retrospect it doesn't look like such a great trade, but initially it looked good (to me).

Thank you everyone for humoring me, I have learned a lot and have a lot to think about.

 

[nyresq]

WHAT IF: you're diving with your manifold iso closed, you're at depth just about to switch to the backup reg on your second tank, when "pop", the neck ring on your second "full" tank goes and you loose your full tank?

assuming you sucked your fist tank down to 1/2, you now have only 1/4 of your total supply to get back up, or if you sucked down the first tank to 1/3, then your remaining supply is down to 1/6... 1/6 will probably not get you up "un-bent" unless you're slinging your deco gas.

by keeping the iso closed, you're defeating the whole purpose of a manifold. you might as well just dive independants and take out the failure point of having the manifold.

I myself dive like Skull, but with my isolator open only about a turn and a half. It is just enough that at depth, gas will flow btw tanks to equalize them, but in a freeflow situation the gas is much slower then a fully open (or even open 3 turns) iso valve. And in an emergency, I can close the iso with two quick turns of my wrist in less then two seconds.

As far as a confined space, if its cramped enough that you can't touch your valves, then you shouldn't be there IMHO....