Isolation Manifold Question

[mahjong]

If there is a failure anywhere at or past (hose, 2nd stage, gauge, etc.) either one of the first-stages, will closing that valve only, without closing the isolation valve, prevent air from the 'other' tank from escaping through that failure point? Or do you absolutely need to isolate the tank with the failure? Here I'm assuming all valves/knobs are in working order and that the failure is at some point in one of the regulators.

Thanks.

[T. Bix]

Think of it this way: the isolator keeps the two tanks joined or seperated when opened or closed. The posts control air to the regulators only. so the answer to your question is: the appropriate response to a free flowing reg or blown hose would be to shut down that post and breath from the reg on the operable post..... now if you blow a burst disk or the tank to valve o-ring (not the din or yoke o-ring) you would shut the isolator to preserve half of your breathing gas.

[MRTdiver]

Hi mahjong,

cavediving.com has a good diagram and explanation...
Manifold Operation (http://www.cavediving.com/how/manifold/index.htm)

[mahjong]

Thanks Bix and MRT.

According to the diagram and explanation at cavediving.com, if there is a free flow/leak in (say) the primary 2nd stage, you close the right post/valve--presumably air stops leaking from the primary. This would suggest that air from the other tank is not traveling through the closed right valve and out the leaking primary. However, the explanation states that: "When one of the regulator valves is turned off (such as would be necessary in the case of a free flow), gas continues to flow from both tanks to the remaining regulator." (I'm assuming "regulator valve" means tank valve?) Air continues to flow from BOTH tanks? If so, this would suggest that, with the valve to the right/primary tank closed, gas from the other/left tank cannot enter through that closed right valve, but gas from the right/primary tank CAN leave through that closed right valve. Is this the case?

[techintime]

closing that valve (with a freeflowing component in the first stage or second stage) will prevent the loss of gas from either tank

[mahjong]

Thanks. And now breathing from the backup regulator, would the air from the primary/right tank (the tank whose valve we just closed) still be available to the backup regulator?


closing that valve (with a freeflowing component in the first stage or second stage) will prevent the loss of gas from either tank

[T. Bix]

Thanks. And now breathing from the backup regulator, would the air from the primary/right tank (the tank whose valve we just closed) still be available to the backup regulator?

Yes.... Don't overthink it! The isolator only "Isolates" the tanks from each other. The posts control only the first stages attached to them. If you don't close the isolator and switch regulators for a failure or "S" drill you will have access to all of your breathing gas. There are only a few reasons to touch the isolator one is during valve drills and the other that comes to mind is a blown/leaking burst disk in which case you'd need to isolate your tanks to preserve half of your breathing gas. You'd only have access to breathing gas from the tank and regulator that is obviously on the tank without the blown disk.

[mahjong]

Thanks Bix.

Good to have it clear. I still don't understand how a closed tank valve/post can allow air to flow out through the manifold, while not allowing air to flow in from the manifold? But I'll take your word for it.



Yes.... Don't overthink it! The isolator only "Isolates" the tanks from each other. The posts control only the first stages attached to them. If you don't close the isolator and switch regulators for a failure or "S" drill you will have access to all of your breathing gas. There are only a few reasons to touch the isolator one is during valve drills and the other that comes to mind is a blown/leaking burst disk in which case you'd need to isolate your tanks to preserve half of your breathing gas. You'd only have access to breathing gas from the tank and regulator that is obviously on the tank without the blown disk.

[Akimbo]

Attached is a schematic diagram for those who are more inclined to understand them. The objective is you can save about half or more of your remaining gas for any single failure. For example:

Leak anywhere past the post/regulator valve seat including the regulator and valve stem itself: Close post valve for offending regulator/valve, isolation can be open.
Cylinder O-ring, burst disk, or isolation valve O-ring(s) connecting post/regulator valves; leak or catastrophic failure: Close isolation valve and use regulator on the good side of the isolation valve. Closing a post/regulator valve serves no purpose.

[Thalassamania]

There are three valves, each with a separate and independent function. If we keep the isolator valve closed, then each "tank" valve (or "regulator" valve, or "post" if you will) controls just the flow to the regulator that is mounted on that valve (post). If you shut a post, gas stops flowing to that regulator. The isolator valve just interconnects the two cylinder. If the isolator valve is open you have one big gas supply, that can be accessed by either regulator assuming that the regulator's post is open. If it is closed you have two separate gas supplies, each only accessible by one or the other regulator, again, assuming that the regulator's post is open.

[techintime]

The valve only stops flow to that first stage. It does not stop the flow into the crossbar. If you think of the crossbar as always pressurized, it will help understand it. Otherwise there would be no way to get all of your gas from either regulator.

[mahjong]

Got it Mania et al, and thanks much!

I now am much more in awe of the technology in those post valves. There must be only one way for gas to enter--through the regulator/1st stage, and this channel can be shut down by closing the valve. But there must be two ways for gas to exit--through the regulator/1st stage and also some other channel that feeds the center crossbar and that is always open. The only way to stop this flow is the close the isolation valve.


There are three valves, each with a separate and independent function. If we keep the isolator valve closed, then each "tank" valve (or "regulator" valve, or "post" if you will) controls just the flow to the regulator that is mounted on that valve (post). If you shut a post, gas stops flowing to that regulator. The isolator valve just interconnects the two cylinder. If the isolator valve is open you have one big gas supply, that can be accessed by either regulator assuming that the regulator's post is open. If it is closed you have two separate gas supplies, each only accessible by one or the other regulator, again, assuming that the regulator's post is open.

[Thalassamania]

I think the best way to think about it is diving separates with a way to cheat and connect them (or unconnect them) on command.

[knowone]

http://www.xsscuba.com/graphics/valves/manifold_lg.jpg

[eelnoraa]

this also means that if there is a failure anywhere in the cross bar, all gas will be lost??!!! all of sudden, it doesn't seem to be so secured. A single failure point to lose all gas.

[Thalassamania]

No, worst possible case is losing half.

[T. Bix]

This is really not that complex....

[halocline]

Got it Mania et al, and thanks much!

I now am much more in awe of the technology in those post valves. There must be only one way for gas to enter--through the regulator/1st stage, and this channel can be shut down by closing the valve. But there must be two ways for gas to exit--through the regulator/1st stage and also some other channel that feeds the center crossbar and that is always open. The only way to stop this flow is the close the isolation valve.

I'm not sure you are quite getting it. The isolator manifold is "upstream" of the post valves. Gas flows through it in either direction regardless of the post valves being open or shut. There's no "one-way" or check valves; the only thing that would prevent gas from flowing into a tank from the crossbar, if the isolator valve is open, is pressure. For example, if you close the isolator, then breathe off of one tank for a while, then open the isolator, gas will flow into that tank. It doesn't matter if the post valves are open or shut for this to happen. The post valves are just regular tank valves. It's just that the junction to the crossbar is before the post valve in terms of air flowing from the tank. And you're right, that channel is always open; that's why you have the isolator valve; to shut down air moving from tank to tank in the event of an emergency leak that involves one tank itself, not the regulator.

You might think of it this way: pretend you have two tanks, each with a valve just like normal. Now pretend you could drill a hole in the side of each tank and attach them with a piece of pipe. That's basically what you have with an isolation manifold, except in the pipe there is a valve so if air were leaking out of one tank, not through the valve but the tank itself, you could stop the flow from the other tank.

[T. Bix]

Got it Mania et al, and thanks much!

I now am much more in awe of the technology in those post valves. There must be only one way for gas to enter--through the regulator/1st stage, and this channel can be shut down by closing the valve. But there must be two ways for gas to exit--through the regulator/1st stage and also some other channel that feeds the center crossbar and that is always open. The only way to stop this flow is the close the isolation valve.

Looking at your profile I have come to one of two conclusions and I'm not sure at this point which one it is: Either 1) You're bored and want to see how many of us you can trick into over explaining such a simple thing or 2) you really have no business owning and diving doubles (which you perport to own in your profile). If it's option number 1, good for you you occupied our minds and hopefully made some folks think about something that many of us take for granted. If it's option number 2 I hope two things for you first that at some point someone actually communicated with you on a level that you understand and second you seek and obtain the training you need to effectively manage your life support system in an emergency. Good Luck

[mahjong]

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?

And just for the profile, since there you went a looking, I am not a tech/cave/wreck diver. I dive short doubles because they give me more air in a manner that trims out for me better than almost any single tank (I am short), keeping in mind as well that I am partial to LP or, at most, MP tanks. I dive old SP regs and prefer not to hit them with 3500+ psi.


Looking at your profile I have come to one of two conclusions and I'm not sure at this point which one it is: Either 1) You're bored and want to see how many of us you can trick into over explaining such a simple thing or 2) you really have no business owning and diving doubles (which you perport to own in your profile). If it's option number 1, good for you you occupied our minds and hopefully made some folks think about something that many of us take for granted. If it's option number 2 I hope two things for you first that at some point someone actually communicated with you on a level that you understand and second you seek and obtain the training you need to effectively manage your life support system in an emergency. Good Luck

[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!

[TSandM]

Actually, even behind you, you're more likely to have a leak from something involving a first stage, than a blown tank o-ring or manifold failure. Hoses come loose, o-rings fail, and if you are in an overhead environment, you can hit and dislodge the first stage (one of the reasons DIN regulators are preferred in those settings). If you aren't wearing a thick hood and thick gloves, it's surprising how often you can localize a leak, either by sound or touch. Of course, we have yet to have a massive one. I really think they are rare.

[mahjong]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!)

I've indeed seen more than a few rather leaky first-stages on divers underwater. There were very steady streams of bubbles--far more than could be mistaken for a bleeding Sherwood first-stage--but these still were not catastrophic leaks. In all but a couple cases the diver him/herself was unaware.





Actually, even behind you, you're more likely to have a leak from something involving a first stage, than a blown tank o-ring or manifold failure. Hoses come loose, o-rings fail, and if you are in an overhead environment, you can hit and dislodge the first stage (one of the reasons DIN regulators are preferred in those settings). If you aren't wearing a thick hood and thick gloves, it's surprising how often you can localize a leak, either by sound or touch. Of course, we have yet to have a massive one. I really think they are rare.

[DA Aquamaster]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!).In general a diver, and in particular a technical diver, should be able to reach their valves.

Where it can get dicey is in a dry suit. If a dry suit diver is hot dropping in a current or dropping into a curerent and pulling their way up a current line, and in either case needs to be substantially negative on entry to begin an immediate descent, then if the valves are turned off, there is a potential for the suit to quickly squeeze and make it impossible for the diver to reach his or her valves. That results in the diver going all the way to the bottom with no gas to the suit, the wing or the regs. That generally ends really badly for the diver.

Obviously in that situation you want to be doubly sure the valves are open and the hoses properly attached before stepping off the boat. I had one incident where a very new and especially "helpful" mate on the boat checked my valves for me while standing behind me before I jumped off the boat. I felt a lot more going on than just the expected stabilizing hand in rough seas and decided to recheck to ensure both regs were delivering gas. Sure enough, the mate had gotten confused with the doubles manifold and had turned both posts off.

I turned around and communicated intensely with him. Something helpful yet educational to the effect of: "If you ever touch my ******* valves again I'll ******* kill you."

The captain then reiterated to him in a slightly more polite manner that you never touch a technical diver's valves as it tends to make them really cranky.

[Akimbo]

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

No, but I check the pressure before and after equalizing before re-closing the isolation valve. I keep the gauge on the primary regulator/cylinder. I suppose if I were worried enough to have a gauge on both regulators I would wear a third independent pony… or switch to surface supplied.

[VooDooGasMan]

No worries just wondering, thanks for the input.

[Akimbo]

Agree. Nice to know the massive failure is rare. Knock on wood, I've never seen one (I have seen a couple divers take the plunge without opening their valves on singles, and one solo diver doing so on doubles--he barely made it back to the surface!)

I've indeed seen more than a few rather leaky first-stages on divers underwater. There were very steady streams of bubbles--far more than could be mistaken for a bleeding Sherwood first-stage--but these still were not catastrophic leaks. In all but a couple cases the diver him/herself was unaware.

I doubt reliable failure rate stats exist but this article in Advanced Diver Magazine provides a useful indication of flow rates for various failures: Life Ending Seconds, 3000 to Zero in 72 Seconds (http://www.advanceddivermagazine.com/articles/lifeendingseconds/lifeendingseconds.html). A table based on this article is reprinted in the SDI Solo Diving Manual, Table 1, Page 38.

In the end it probably doesn’t matter what the stats are. People are satisfied to make some of their daily safety decisions based on probability, driving on a freeway for example. Yet other decisions necessitate, in their view, a backup or a backup to a backup. How different individuals respond to the self-preservation instinct is interesting.