isolator open or closed?

[dennisgrimm]

nyresq:
Like i have just mentioned, I am leaning towards diving with my isolator open. In fact, I just removed my second SPG and will be doing my next dives with the iso opened a bit. However, I will again play the devil's advocate and argue the other side.

First, we both know that a neck o-ring failure can happen but is very unlikely. Second, diving independants you would only use 1/3 of your first tank before switching to your second tank. Then you would use 2/3 of your second tank and switch back to your first. You would then complete your dive on your first tank with 1/3 remaining in both. This is the method of diving independants that was taught to me. So, in your scenario if a failure occured at the first switch you would still have 1/3 of your total gas remaining and you would would only be 1/4 into your dive. Not a problem. Following the above outlined procedure, the worst case scenario would be to have a failure like you described at your turn around point. You would have used 1/3 of your first tank and 1/3 of your second tank and would have 1/3 of your total gas supply still remaining after losing a tank (either). Again, no problem and you are not too worried at this point because you didn't have to close your isolator (already done) and you know you have 1/3 to get out. Make sense?

Think that is bad? The above mentioned worst case scenario is even worse with an isolator open. Follow me here... you are at your turn around point and have consumed 1/3 of your total gas. You lose a neck o-ring and quickly shut down your isolator. One tank is toast and you now have less than 1/3 of your gas supply remaining because you have lost a bit of gas in the process of shutting down the isolator. How much you lose will depend on how quick you can shut your isolator down and that will depend on what you are doing at the time of failure. On top of that your SAC rate will be up (mine would be anyway) because you just had to close your isolator and your leaking post to discover that it is still leaking.

The point is, don't lose a neck o-ring at the turn around point. ut:

The downside of using independant is the associated task loading and extra equipment all of the time and the benefit is the possible reduced task loading durning an emergency. Proper gas managment should allow you to have enough gas in either situation.

 

[RichLockyer]

OTOH, in a cave penetration, it may be no issue at all since you may be diving stages.

IIRC, the director of the WKPP once indicated that anyone who surfaced with less than 2/3 backgas was immediately dumped from the project. The dives are done on stages (1/2 plus 200psi), and backgas only used in emergencies, or perhaps during a stage drop/pickup.

 

[Exorcist]

This has got to be a troll. Diving an isolation manifold with the isolator off. Having your buddy restuff your long hose. Considering the long hose wrapped around your neck as too much clutter. Swimming away from a panicky buddy to prevent him from taking your primary, etc. Think this newsgroup deserves its reputation as home to the terminally clueless.

 

[gilou28]

The Skull, or others that dive with that approach

One question on this interesting approach....


Once, in my first dives, I was in single and did not open completely the valve on my tank.

RESULT: at abound 50 feet, I had trouble breathing and after 4 up and down from 50 feet to 30 feet, I realised that my valve was not completely opened.

QUESTION: wouldn't the same thing be happening to the isolator preventing equalisation between the two tanks ???

hummm. interesting

 

[cattrax]

With 5 months and 55 dives to your credit you have accelerated to doubles and the task loading that goes with them. Maybe too quickly. I would find a steel 120 and put an H valve on it. Put both of your regs on it with a long hose on the primary and the backup (octo) hanging around your neck with a piece of silicone tubing and go out and dive, get experience. You're trying to go too fast. Learn to manage your air supply through proper breathing. You don't need doubles till you learn to stage dive. Or are you already doing that too?

 

[DeepScuba]

Gilou28:

Not really. You wouldn't notice any breathing difference since (assuming your tank valve was full open) you don't have a restriction into your first stage, so the full tank pressure with ample flow capability would be present to your regs.

The only thing that would, theoretically happen would be a VERY MINOR "lag" in tank equalization. As in, non existant, unless the one tank o-ring was blown, the reg on that side is free flowing, and the isolator is 99% shut!! You're not "flowing" (Volume) a whole lot through the isolator under normal breathing conditions.

 

[dennisgrimm]

Exorcist:
I assure you I am not a troll. And by troll I mean that I would start a thread simply to cause argument. I think that just about every thread on this board has a "troll" accusation on it somewhere. Thank you for being the one to do it here, it contributes a great deal to the conversation.

I started this thread because I have been lurking here for a while and from what I read no one dives with the same procedures or setup as what I was taught. I wondered why and posted about it.

Since starting this thread I now better understand why people dive with the iso open and are going to try it myslef.

I am still going to donate my octo. Therefore, the octo is the only sensible place to have the long hose. What else do you do with a 7ft hose if you are not going to breathe off of it? I like the fact that my buddy can get to my alternate from in front and behind all without having to get my attention right away. I don't like the idea of my buddy going for the reg in my mouth. The last thing I need underwater is a panicky diver on my like a fat kid on an m&m. I don't know about you, but in my rescue course I was taught not to get within reach of a panicky diver on surface, so why would it be different underwater? When I said I would swim away from a panicky diver, I meant swimming away while facing them and offering my octo. I did not mean turning tail and leaving them. I have heard some people say that they don't dive with a buddy that will panick. I don't think you can accuratley predict how others will react when they are OOG.

I have attached a pic straight out of the ANDI Advanced Diving Activities book that is standard reading for the TSD course.

cattrax:
You are right, i have advanced quickly. Part of the fun of diving for me is the challenge to do something new (along with all the cool stuff to see underwater). Maybe my inexperience shows in what I am doing. That is why I am soliciting the opinion of more experienced divers, like yourslef (and learning a great deal). I did not start diving with doubles because I am an air hog. Quite the opposite actually. Of the people I dive with I use almost the least gas. Why doubles then? for the challenge and to get practice because my first tech course (ANDI TSD) starts in a week, the same reason I have practiced using my lift bag. I am not doing stage diving yet.

 

[chrpai]

dennisgrimm once bubbled...
Boogie:

Isn't it concievable that I might lose a significant amount of gas such that I don't even have 1/3 of my gas left? Know what I mean? I have contained the gas loss but may not have enough gas left to do my deco.

Thats what you have a buddy for. The final 3rd isn't for you, its for him. And his final 3rd is for you.

 

[dennisgrimm]

weird... the pic I uploaded isn't showing

 

[IndigoBlue]

dennisgrimm once bubbled...

Since starting this thread I now better understand why people dive with the iso open and are going to try it myslef.

Good. I believe that is the right answer. I keep my manifold opened 5 turns of my wrist. that way I can shut it down faster if I need to. However some agencies recommend keeping it opened all the way.

dennisgrimm once bubbled...
I like the fact that my buddy can get to my alternate from in front and behind all without having to get my attention right away. I don't like the idea of my buddy going for the reg in my mouth.

There are pros and cons either way you look at it. For example, I am not comfortable with a reg out on my shoulder somewhere that it can get knocked around, although I have a friend who dives configured exactly like this.

I prefer to breathe off the long-hose octo myself, and donate that when needed by a buddy, with my backup on a necklace about my neck, close to my face and under my constant observation.