Isolation Manifold Question

[VooDooGasMan]

Fill your tanks, fill with ISO closed, fill one side, open ISO and hear the air. when you hear the air and understand what you open it might get close to home for you. I fill one side then switch to other, let cool then open ISO and fill for top off.

Do you put nitrox in your tanks.

Hey shortie are you divng SP 108 or 109 regs and what 1st stage.

 

[mahjong]

Thanks, Gas. All this has been educational for me.

Air only.

Both 108's (earliest model) and 109's (adjustable, but internally upgraded to balanced). With the shortie MP72's, I use two early MK10's. (By "shortie" you were referring to the MP72's, right? ;-)

Fill your tanks, fill with ISO closed, fill one side, open ISO and hear the air. when you hear the air and understand what you open it might get close to home for you. I fill one side then switch to other, let cool then open ISO and fill for top off.

Do you put nitrox in your tanks.

Hey shortie are you divng SP 108 or 109 regs and what 1st stage.

 

[Rick Murchison]

I don't recommend filling tanks with the isolation valve closed. There's nothing to be gained from it, and there are several bad things that can happen, especially when dealing with gasses other than air.
Rick

 

[halocline]

Thanks, Gas. All this has been educational for me.

Air only.

Both 108's (earliest model) and 109's (adjustable, but internally upgraded to balanced). With the shortie MP72's, I use two early MK10's. (By "shortie" you were referring to the MP72's, right? ;-)

I've used MK5s and 10s with a 3442 PSI tank many times. Just make sure that whoever services it uses a 90 duro o-ring for the HP piston. You really shouldn't have any problem. But, of course there's nothing wrong with LP tanks either; my favorites are LP72s. I have a set of doubles and a few singles.

I agree that in general you should not fill doubles with the isolation valve closed, although maybe voodoo gas guy was just suggesting it as a way of learning more about the valve. In fact, filling with the iso valve closed, then forgetting to open it is kind of a classic screw up that leaves the diver with only half a fill.

 

[PfcAJ]

That killed a guy in Florida a few years ago.

 

[DA Aquamaster]

I appreciate your point. In a private doubles training class, I have learned "when X happens, close the post valve," etc. Recently, in a conversation at a dive site, someone suggested something counter to what I learned, namely "when X happens, close the isolator valve." At that point, I found myself falling short on an understanding, not of the rule I learned, but of the mechanical underpinnings of the rule--ie, the precise mechanical/internal functioning of the post valve that 'effects' the "how" and "why" of the rule.

I would say that, after reading all these replies, most people understand the rules. However, it strikes me that most people understand them more in an intuitive sense, rather than a mechanically rigorous one, and this is fine. Some people understand them in terms of analogies--"think of it this way...." At least one of the diagrams offered was pretty but entirely impertinent. Suffice it to say that not everyone seems to understand thoroughly the mechanical properties of the post valve that explain the how and why--or at least most people haven't offered such an explanation (I'd have to go back and review, but Halocline's hit me as most helpful in this mechanical regard). This is what I was looking for. Maybe I played the devil's advocate a little bit in the hope that someone might hit the nail on the head, at least for me. And maybe in doing so this made me seem more ignorant than at least I hope I am. In any case, your point is still well taken. That said, I'm still dying to ask my technician to explain to me the mechanics of the post valve. Does this mean I should shelf my doubles rig?

I think you are correct to a large extent in that many divers, including technical wreck and cave divers learn things by rote and do it that way because it's the way it;s done/taught to them. For some of those individuals doing it a particular way is done because someone they highly respect says so, and that's good enough for them. That is however an "authoritarian" method of "knowing" something that will NOT be sufficient for a diver who prefers to arrive at (what is usually) the same conclusion after fully understanding the mechanics, science and physics involved, then wargaming the variosu scenarios and possibilites.

Neither one is "wrong" but there are pros and cons. When the **** hits the fan, the rote/authoritarian learner is going to ru8n the drill and muscle memory is probably all he needs - as long as the scenario fits the training. The thinking diver is not going to default to th xrill as fast, but instead may spend some time working the problem. That takes time and may cost gas, but it also may save gas if the solution is reached faster than runnning an drill on the manifold, and it may better address non standard failures and scenarios. Both approaches work but they approach problems from different perspectives.

----

I probably have a picture of a cut-away valve somewhere they may help explain the mechanics a bit more. I'll post it later if i can find it.

----

A failure in the isolator bar is no a big deal as it would be on one side of the isolator or the other and would only result in half the gas being lost. A failure of the isolator valve itself would however be a total gas loss event. There was lots of agonizing and teeth gnashing over this in the late 70s/early 80s regarding the pros and cons of independent doubles versus single outlet manifolds versus dual outlet non isolated manifolds versus cheater bars versus isolator manifolds. The short story is that only isolator manifolds and independent doubles that have remained as accepted options for technical diving (although I know one cave instructor who still dives a non isolator dual outlet manifold).

 

[TSandM]

You know, in the OP's defense, when I got my first set of doubles, I was confused about exactly how the manifold worked. I learned from a friend. I actually don't remember any of my classes actually going through and talking about HOW a manifold worked -- we just learned what to do when different things happened. Of course, the rationale behind those interventions relied upon an understanding of the equipment, but you could just learn them by rote.

Mahjong, there is a school of thought that any significant gas loss from behind your head should immediately prompt you to close the isolator. There is another school that teaches that it's okay to try to localize the gas loss, or try closing the right post first. There are very good arguments in favor of of each approach, and each has its weaknesses. Some of it may have to do with how quickly you can close posts -- if you are desperately struggling to get anything closed, the isolator might be the better first choice (and I have seen technically trained people who are slow and laborious to get any post closed).

Closing the isolator does nothing to solve the leak, but protects the tank on the other side of the isolator from the problem from any further gas loss. Closing a post CAN solve the leak, thus preserving gas in both tanks; but if you choose the wrong one, or if the failure is one of the rare ones that cannot be addressed by closing a post (tank o-ring or manifold failure) then you continue to lose gas from BOTH tanks until you can isolate.

This may at least explain why you have gotten two different kinds of advice with respect to how to manage leaks behind your head. (Obviously, if the leak is in front of you, you know exactly which post to close!)

 

[Akimbo]

You know, in the OP's defense, when I got my first set of doubles, I was confused about exactly how the manifold worked...

Exactly correct. "Human factors" was not a design consideration when the manifold was produced. If it were, a flow diagram would be forged/embossed into the manifold body. I spent most of my career working with complex piping systems and there is no way I would "assume" where the flow paths are in an isolation manifold without playing with it to confirm.

I think you are correct to a large extent in that many divers, including technical wreck and cave divers learn things by rote and do it that way because it's the way it;s done/taught to them. For some of those individuals doing it a particular way is done because someone they highly respect says so, and that's good enough for them. That is however an "authoritarian" method of "knowing" something that will NOT be sufficient for a diver who prefers to arrive at (what is usually) the same conclusion after fully understanding the mechanics, science and physics involved, then wargaming the variosu scenarios and possibilites.

Neither one is "wrong" but there are pros and cons. When the **** hits the fan, the rote/authoritarian learner is going to ru8n the drill and muscle memory is probably all he needs - as long as the scenario fits the training. The thinking diver is not going to default to th xrill as fast, but instead may spend some time working the problem. That takes time and may cost gas, but it also may save gas if the solution is reached faster than runnning an drill on the manifold, and it may better address non standard failures and scenarios. Both approaches work but they approach problems from different perspectives....

Well stated. People learn differently and bring different life experiences to the process. I will say that some individuals evolve from rote learner to thinking diver as their experiences allow, but rarely the other way around.

Just to throw an additional variable into the discussion, I keep my isolation valve normally shut. The practice is more common in the UK and is sometimes called progressive equalization.

Following up on Sat Diver and Bob/Grateful Diver's comments: Aside from protection, the second reason for valve-down is the way I use the isolation valve on doubles, which seems to be different than just about everyone in the US.

For me, isolation valve access must be quick, comfortable, and covenant because I open and close it 3-6 times per dive. An ex-British Navy diver first turned me on to progressive equalization. To me it makes perfect sense. You start the dive with the isolation valve shut. Once you breathe down the primary cylinder you reach back, equalize the two cylinders, and close the isolation valve again. The reserve aspect is a hallmark of most triple and quad cylinder rigs used by Cousteau and is far more effective than the early J/Reserve valves.

Each equalization can correspond with a pre-determined event based on the dive plan. For example:

1. Start meandering back toward the boat
2. Look more aggressively for the anchor
3. Stop fooling around and find the anchor
4. Forget the anchor and leave bottom right now

IMHO, the entire failure mode analysis behind the isolation manifold would be better served by leaving the isolation valve shut. If an O-ring, hose, or burst disk fails, gas is only lost from the one cylinder. You can still shut the regulator stop valve if the failure is upstream and potentially safe more gas -- especially when you can't react immediately or misdiagnose the problem on the first try.

 

[VooDooGasMan]

Akimbo do you have one pressure gauge for each post or one total.

 

[mahjong]

Thanks to everyone for the first-rate education. You guys are an invaluable resource.

TSandM: It strikes me as defensible to make the distinction between a significant leak behind your head vs one in front of you. In practice I suspect it might be quite difficult to diagnose a leak behind your head. If you can even detect the leak then perhaps it's more likely than not going to be significant, in which case it's more likely than not going to be one that requires isolation (eg, blown burst disk, tank O-ring).

DA: Those are some insightful observations on the different reactions of the rote learner versus thinking diver--when it hits the fan.

And now we have progressive equalization in the mix.

Maybe Bix was right--best not to think too much about all this ;-). Easier said than done for me, though. I've now much to think about and appreciate it very much.

Thanks again to all!