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Scotttyd
05-14-2008, 21:40
Which is better? Advantages and disadvantages of both? All I have ever seen around my local is manifold?

CompuDude
05-15-2008, 00:42
Independents have their proponents (not many, but they're out there), and there are places where it's a reasonable option due to lack of other options, but tracking the gas levels in two tanks individually, switching back and forth at specific points to maintain dive-appropriate levels in each tank, it all gets a LOT more complicated, and is considerably more task-loading than a manifold, which turns the two tanks into one big one and sucks them down equally (while maintaining the ability to split them again in an emergency).

The technical community has mostly settled on the isolation manifold as the preferred, safest option. (Mostly.)

navyhmc
05-15-2008, 03:34
Can't say it much better than Compudude. The isolator makes a manifold the way to go. The only positive to independant doubles is if you have a complex gas set up and don't need more than one tank of a specific gas.

IMO, isolator is the way to go.

LiteHedded
05-15-2008, 07:34
if you're diving independent doubles why not just sidemount?

mm_dm
05-15-2008, 07:40
Independents have their proponents (not many, but they're out there), and there are places where it's a reasonable option due to lack of other options, but tracking the gas levels in two tanks individually, switching back and forth at specific points to maintain dive-appropriate levels in each tank, it all gets a LOT more complicated, and is considerably more task-loading than a manifold, which turns the two tanks into one big one and sucks them down equally (while maintaining the ability to split them again in an emergency).

The technical community has mostly settled on the isolation manifold as the preferred, safest option. (Mostly.)

I agree. I know a couple of guys who are heavy cavers who use independent doubles. Each tank has and H or Y valve for redundant regs as well. :smiley29:That's their thing...seems like a bid PIA IMHO. I'll take my isolation manifold, thank you very much.:smiley20:

Scotttyd
05-15-2008, 07:49
When diving with a manifold, is there any way a single malfunction can cause a complete loss of air in both tanks? If that is the case, is not some sort of redundancy needed?

Geoff_T
05-15-2008, 08:54
When diving with a manifold, is there any way a single malfunction can cause a complete loss of air in both tanks? If that is the case, is not some sort of redundancy needed?


Somebody may have a more concise answer there but I think that unless the manifold or isolation valve actually fail and rupture or the isolation valve locks up for some reason it is impossible. Unlikely though it may be....

MSilvia
05-15-2008, 09:06
When diving with a manifold, is there any way a single malfunction can cause a complete loss of air in both tanks? If that is the case, is not some sort of redundancy needed?
I suppose a catastrophic explosion that sheared off both tank valves would do it, but anything that caused that to happen would likely also remove your head from your neck, so assuring redundancy wouldn't be all that critical in that case.

Lest you worry that that might actually happen, an explosion like that would probably require the use of explosives.



Somebody may have a more concise answer there but I think that unless the manifold or isolation valve actually fail and rupture or the isolation valve locks up for some reason it is impossible. Unlikely though it may be....

If the manifold ruptures (not that it ever would... it's steel, and designed for use with high pressure gas), you should still be able to isolate and shut down the post on the rupture side. If the isolator valve failed, that wouldn't cause loss of air unless it also vented, but that would be a highly improbable multiple failure scenario, and not something that would "just happen". I've never heard of a single case of anything like that.

mm_dm
05-15-2008, 09:10
I guess both tank neck o-rings could go at the same time, or something weird like that. Your redundancy comes from your buddy's reserve or from your stage if you are at a depth where that stage can be utilized and you have it available. OOA drills should be practiced regularly with your buddy, preferably before descending on the dive.

elijahb
05-15-2008, 13:49
when you dive side mount tank you don't use a manifold so why not aply the same priciples of diving side mounts as back mount doubles?

MSilvia
05-15-2008, 13:54
when you dive side mount tank you don't use a manifold so why not aply the same priciples of diving side mounts as back mount doubles?
What principles would those be?

CompuDude
05-15-2008, 14:17
when you dive side mount tank you don't use a manifold so why not aply the same priciples of diving side mounts as back mount doubles?

Side mount is generally the province of extremely experienced wreck and cave divers who have been doing it long enough that the extra complexity is do-able.

It's not something that new divers would be advised to take on.

fire diver
05-15-2008, 22:28
The reason the vast majority of doubles divers go with a manifold is becuase it is so much safer and easier. I started out playing with independent doubles when I first started using double tanks. It wasn't worth the hassle to me and I quickly bought a manifold.

There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

It's not that independent doubles are bad, a manifold is just better for most.

Dive-aholic
05-16-2008, 05:24
Alright, a brief lesson on sidemount (or independent doubles):

It's not difficult at all. And it's not reserved for the extremely experienced caver or wrecker. It's actually quite easy and much safer than manifolded doubles. I used to dive manifolded doubles and when I went solo into a cave, I would bring a buddy bottle along. The possibility of having a manifold failure and losing gas from both bottles while doing a shut down (yes, you will lose a lot of gas, a valve shut down goes smoothly when you're practicing it, but try doing one while you have a major failure happening behind you...it will take you a minute or 2 to get the issue isolated and resolved, and while that's happening you're losing gas from both tanks) is there. If you experience this kind of failure, you want a completely independent gas source as a back up. With independents or sidemount bottles, you have 2 completely independent gas sources, so there is no need for a buddy bottle.

As for the task loading. There's really not a whole lot of task loading. Breathe down your right tank by 500-600 psi, switch to left tank, breathe that down by 1000-1200 psi, switch to right tank, breathe that down by 1000-1200psi, switch to left tank. Your dive will be over before you have to switch back. That's 3 reg switches over the course of an hour or so. How complicated is that? I've only been sidemounting since September, but haven't looked back since then. I encourage everyone to give sidemounting a try. It's a lot more comfortable than backmount and is not difficult at all. Whether anyone wants to admit it or not, sidemount is the new thing. When I first started sidemounting, I saw very few divers in sidemount rigs. Just since the beginning of this year, I've seen more sidemount divers than backmount divers. In fact, backmount is becoming the rare sighting...at least where I dive. And sidemount doesn't mean small spaces. I sidemount in big passage all the time. I sidemount in OW. It's just more comfortable...even more comfortable than a single tank rig. So please, don't talk about sidemount like you know what you're saying unless you do sidemount. And my guess is that no one here that's commented on it does. No offense meant to anyone. I just hate the misconceptions people have about sidemount diving.

coyote
05-16-2008, 06:58
<snip>
There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

That's the only real reason I can think off. Far from home and the local shops only rent single AL80. Maybe some more diving with them would have improve matters, but I found the whole thing cumbersome and not fun.

Rainer
05-16-2008, 18:39
It's actually quite easy and much safer than manifolded doubles.

Give me break. Please cite some examples of actual dives where someone died who would have lived if he'd been side-mounting as opposed to using an iso-manifold.

If you're solo diving, then sure, stay away from the iso-manifold and go independents (or better yet, side-mount) if you want. For those diving in experienced teams, an iso-manifold is completely safe, and obviously easier than side-mount or independents (breathe vs. breathe and switch and switch and switch...).

Rainer
05-16-2008, 18:40
<snip>
There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

That's the only real reason I can think off. Far from home and the local shops only rent single AL80. Maybe some more diving with them would have improve matters, but I found the whole thing cumbersome and not fun.

Bring a manifold with you. Done.

elijahb
05-16-2008, 20:40
<snip>
There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

That's the only real reason I can think off. Far from home and the local shops only rent single AL80. Maybe some more diving with them would have improve matters, but I found the whole thing cumbersome and not fun.

Bring a manifold with you. Done.

Don't you need a different valve?

Dive-aholic
05-17-2008, 00:47
Give me break. Please cite some examples of actual dives where someone died who would have lived if he'd been side-mounting as opposed to using an iso-manifold.

If you're solo diving, then sure, stay away from the iso-manifold and go independents (or better yet, side-mount) if you want. For those diving in experienced teams, an iso-manifold is completely safe, and obviously easier than side-mount or independents (breathe vs. breathe and switch and switch and switch...).

I never stated someone died using a manifold and wouldn't have had they been sidemounting. I was responding to fire diver:


The reason the vast majority of doubles divers go with a manifold is becuase it is so much safer...

If is was so much safer to dive a manifold then why would I need a buddy bottle in that situation but not solo. I also never said it's easier. I said it's not difficult.

I'm not saying that sidemount or independent doubles is for everyone. It's not. But I don't like to read these fairytales about either one that are merely people who don't know what they're talking about spewing at the mouth. It's the same thing as the jacket proponents that have never been in a bp/w saying you can't stay upright on the surface with a back inflate. If you want to argue, that's fine, but please read my post carefully and don't take it out of context...







<snip>
There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

That's the only real reason I can think off. Far from home and the local shops only rent single AL80. Maybe some more diving with them would have improve matters, but I found the whole thing cumbersome and not fun.

Bring a manifold with you. Done.

Don't you need a different valve?

Yes...actually 2 valves. And not many dive ops will be willing to pull valves off their tanks to accommodate you.

Rainer
05-17-2008, 10:31
Give me break. Please cite some examples of actual dives where someone died who would have lived if he'd been side-mounting as opposed to using an iso-manifold.

If you're solo diving, then sure, stay away from the iso-manifold and go independents (or better yet, side-mount) if you want. For those diving in experienced teams, an iso-manifold is completely safe, and obviously easier than side-mount or independents (breathe vs. breathe and switch and switch and switch...).

I never stated someone died using a manifold and wouldn't have had they been sidemounting. I was responding to fire diver:


The reason the vast majority of doubles divers go with a manifold is becuase it is so much safer...If is was so much safer to dive a manifold then why would I need a buddy bottle in that situation but not solo. I also never said it's easier. I said it's not difficult.

I'm not saying that sidemount or independent doubles is for everyone. It's not. But I don't like to read these fairytales about either one that are merely people who don't know what they're talking about spewing at the mouth. It's the same thing as the jacket proponents that have never been in a bp/w saying you can't stay upright on the surface with a back inflate. If you want to argue, that's fine, but please read my post carefully and don't take it out of context...







<snip>
There are times when using ind-doubles might be needed though. If you are traveling and can't use your own tanks, but need the volume of twins, then independent doubles can be a viable option. But as stated earlier, it does require more equipment and some different skills to use safely.

That's the only real reason I can think off. Far from home and the local shops only rent single AL80. Maybe some more diving with them would have improve matters, but I found the whole thing cumbersome and not fun.

Bring a manifold with you. Done.

Don't you need a different valve?

Yes...actually 2 valves. And not many dive ops will be willing to pull valves off their tanks to accommodate you.

Try reading again. It's not ME saying it's much safer to dive an iso-manifold, it's YOU who is saying it's much safer to dive side-mount. That's BS. The only test of that would be saved lives of one system over the other. They both clearly work. But it's a fact that an iso-manifold is going to be at least somewhat less task demanding than independents or SM.

And no, you don't need two extra valves with a manifold. That's what the manifold includes. I didn't say just to bring an iso bar. And PLENTY of OPs will let you do just that. Have you bothered to actually try? I know the place we used in Bonaire was willing to pull two valves (it takes five seconds once the cylinders are drained).

LCF
05-17-2008, 11:13
I think it's really hard to make hard and fast statements about what's safer, simply because the kinds of catastrophic failures that really test any configuration are so rare.

I like the fact that, with an isolation manifold, I retain access to all of my gas in the face of the most common types of failures, which are post failures. Of course, I have added a couple of O-rings and another valve, but they aren't moving parts and don't get taken apart and put back together often (as first stages are put on valves, for example). If I do lose a burst disc or tank o-ring, yes, I will lose some gas out of the other tank while I'm getting it dealt with, which is why my buddy is carrying gas for me.

If I dove solo, I might have a different point of view. And certainly, one advantage of sidemount is that you are less likely to ram your valves or burst discs into anything :)

Dive-aholic
05-17-2008, 16:45
Try reading again. It's not ME saying it's much safer to dive an iso-manifold, it's YOU who is saying it's much safer to dive side-mount. That's BS. The only test of that would be saved lives of one system over the other. They both clearly work.


Okay, I'll give you that it may not be much safer, but taking away the failure points of the iso-manifold does make it safer, or would less risky be a better phrase.


But it's a fact that an iso-manifold is going to be at least somewhat less task demanding than independents or SM.

It may be less task demanding during the course of a regular, no issue dive. But when it counts, during a valve shutdown to save your gas, independents and SM are much less task demanding than an iso-manifold. You may end up having to do multiple shutdowns just to figure out where you're losing gas. All you have to do with independents/SM is find the gas loss source and shutdown one valve. I'd rather take on a little more task during a uneventful dive.


And no, you don't need two extra valves with a manifold. That's what the manifold includes. I didn't say just to bring an iso bar. And PLENTY of OPs will let you do just that. Have you bothered to actually try? I know the place we used in Bonaire was willing to pull two valves (it takes five seconds once the cylinders are drained).

Alright, I was thinking just the iso bar when you said manifold. But I don't know about PLENTY of OPs. Yes, there are some out there, but you'd be hard pressed to even find half of most typical ops that would do it. There's only one shop I know of in Belize that would do that. Lots of shops in the Riviera Maya, but try Cancun and you'll have a much more difficult time. Actually, I think you'd be hard pressed to even find a shop in some locations that know what an iso-manifold even is!

Dive-aholic
05-17-2008, 16:55
I think it's really hard to make hard and fast statements about what's safer, simply because the kinds of catastrophic failures that really test any configuration are so rare.

Agreed. For the most part, this is a hypothetical discussion about the what-ifs.


I like the fact that, with an isolation manifold, I retain access to all of my gas in the face of the most common types of failures, which are post failures.

You'll lose gas from both tanks while you are shutting down. You only lose gas from one tank with independents.


Of course, I have added a couple of O-rings and another valve, but they aren't moving parts and don't get taken apart and put back together often (as first stages are put on valves, for example).

I just broke down a set of doubles for a friend last Monday. The tanks were VIPed in February. The double o-rings on both ends of the iso bar were flat. His iso bar was stationary, unlike the way I used to keep mine when I dove manifolded doubles (I liked being able to twist my iso bar). And, yes, they were replaced during the VIP (maybe it's those cave fills that flattened them.....)


If I do lose a burst disc or tank o-ring, yes, I will lose some gas out of the other tank while I'm getting it dealt with, which is why my buddy is carrying gas for me.

If you double disc, you'll never lose a burst disc.....


If I dove solo, I might have a different point of view. And certainly, one advantage of sidemount is that you are less likely to ram your valves or burst discs into anything :)

It is a different mind set when you're down there alone. And here's the thing, no matter how well you train to dive in a team, stuff happens. A silt out can quickly break up that team and make everyone a solo diver...no matter how close to each other you are... One foot of distance can quickly become 10 feet in no to low visibility (haven't you posted some experiences in the PNW like that?)

Again, I'm not advocating sidemounting for everyone. Actually, the less people that sidemount, the more less traveled passage I have all for me. But there are distinct advantages to it when stuff happens.

in_cavediver
05-17-2008, 21:32
Having dove both sidemounts and iso-backmounts, all I can say is they are different solutions to a problem. Neither is ideal. One is better is some cases, but not all.

Backmounts:

1) Can access all gas from both regs
2) In a single failure scenario, most of the time you keep access to all the gas. Sometimes you lose 1/2 and in one case, broken isolator, you lose all your gas.
3) They are heavy and travel as a set

Sidemounts
1) each reg give access to 1/2 your gas
2) A faillure generally takes 1/2 you gas. No single failure will take all of you gas.
3) Valves and gear are literally right in front. No hassles reaching for valves or identify leaks.
4) Tanks are independent
5) More tasks to accomplish.
6) Presents a different profile for access

I personally believe any tec diver worth anything should be able to handle independents. If you can't handle the task loading, you should really rethink your ability to do tec type dives.

Backmounts have a highly refined concept of rigging. It doesn't make much differnence if you call it hog or DIR or whatnot, most tec doubles look the same and are rigged the same. Sidemount is a new and evolving gear trend. Its been around a long time in a niche area but with the changing demographics of cave divers, many are looking to reduce the out of water wieght they have to carry and doubles are the big target.

Dive what you like but sidemounts can offer a significant safety advantage over backmounts in some cases. If you want an example - solo cave diving. Sidemount=2 tanks. Traditional backmounts = 3 tanks. Sidemounts can also be a significant conveience as well. Think dives from small boats - 2 singles vs one set of doubles. Singles are easier to deal with.

Roughwater
06-15-2009, 20:47
Hi Guys,

Sorry to revive such an old thread, but I've been contemplating Manifolds vs Independents for a while now, and would like some comments on what I have summarised todate.

Personally - I can't see an overwhelming benefit to manifolds. (I can see that both have benefits and disadvantages), but many divers out there seem to think manifolds are the only way to go and are much safer. (I see them as being more dangerous). While it doesn't concern me that I don't agree with them, it does concern me that I can't understand where they're coming from (and thus believe that I've 'missed' something), so I was wondering if you guys could please review my summaries below and comment.

(Keep in mind I am a cave diver - but I will try to discuss on general diving)...

Manifold Benefits

1a- In the event of a reg failure, you can still have access to all gas in both tanks.

1b- No need to change regs throughout a dive. Donating reg will always be in your mouth.

1c- Always same amount of air in both tanks (so if donating air you don't need to worry about one running out of air before another).

1d- Reduced task by not needing to swap regs and evenly decanter.


Manifold Concerns & Disadvantages

2a- A single reg failure can cause you to lose all your air if you are unable to access your posts or isolation valves. (I have seen many struggle with this too). Also needs to be taking into consideration in restrictions where you may not be able to access your valves.

2b- More costly to setup and less versatile. Unable to separate tanks easy to use as singles for other dives (Yes - I'm a cheapskate) :smiley2:

2c- If isolation valve is not open, diver can find that he's only received 1/2 a fill. (I've seen this happen on numerous occasions).

2d- Left Post roll-off (in overhead environments).

2e- If you lose concentration and run out of air, there is no alternative backup to quickly switch to - completely rely on your buddy.

2f- More costly to setup.


Independent / Sidemount Benefits

3a- Completely independent. No single failure will cause you to lose more than 1/2 of your air supply. (If breathing down and swapping regs correctly).

3b- If you lose concentration (photography, etc) and run out of air, you can switch immediately to your other tank - then get close to your buddy and call the dive. You'll never run out of air in both tanks simultaneously.

3c- Easy (and not costly) to setup.

3d- Can donate a full tank (if sidemount) to another diver easily.


Independent Concerns & Disadvantages

4a- Decision on which hose to donate (as your donating hose may not be in your mouth at the same time). (However I've found that simply donating your breathing hose regardless to start with, and then 'swapping' later if necessary is not a problem).

4b- Can lose 1/2 of your gas supply for something as simple as a reg failure.

4c- Additional task. (swapping regs during the dive). (Although I've never seen this as a real problem and becomes second nature very quickly when diving indi's)







I have heard of a diver doing a course going through a restriction with manifolds whilst donating air to another diver. His left post rolled off (the post he was breathing from) and he couldn't access it to turn it back on due to the restriction. He managed to get to his buddy and retrieve his other reg - but it was a serious moment.

Personally - if diving to a rule of thirds or quarters, I can't see a significant benefit with a manifold setup. Many others seem to, so I was hoping that someone could please comment on my summaries above to help me understand 'the other side' so to speak. :smiley2:

Edit: Added reference marks (ie, 1a, 1b, etc against points to make certain points easier to refer to for replies)

CompuDude
06-15-2009, 21:18
I'm not to weigh in, beyond adding these things to consider:

1) Depending on your diving experience and ability to multitask, maintaining the proper gas supplies in two independent tanks is considerably more work than with manifolded doubles. This may or may not be an issue to you, but in technical diving where doubles are required, the ability to KISS tends to be highly valued.

2) The people who tend to promote manifolds most religiously tend to be those who also advocate the buddy system most religiously... at least for tech diving. If you're diving solo, and plan to continue doing so, even in the technical realm, some of the arguments for the manifold are less valid. (Your buddy(ies), who theoretically have your backup gas in the event of such a catastrophic failure, don't exist in that scenario)

3) Don't be a cheapskate. Not when it comes to overhead environments. Seriously. Save it for the reefs.

Roughwater
06-15-2009, 23:08
Hey CompuDude,

Thanks for your reply - greatly appreciated...

On what you commented:

1) Personally, I have never found needing to decanter the cylinders being considerable more work - but very basic and simple (same with most of the divers I have dived with). Maybe that's just us - but while I have seen this argument used I am yet to meet someone who will put up there hand and say 'yes - I have found it considerable more work'. (I would be quite interested if there are people willing to do that, just so I know it's not just a theoretical problem but a real one for some divers). :smiley2:

2) Even with strong emphasis of the buddy system in mind I struggle to see how manifolds are significantly safer and would appreciate some examples to get my (thick) head around.

The only 2 things I can think of are with the 'official donor' hose always being in the mouth and that they're both breathing off the same air supply - but can't see this as being a significant advantage.

(Again, this may have to do with my personal experience and that of my dive buddies where we went through both deep cavern and cave courses with independents instead of manifolds and had no problems. The hose in the mouth was donated first, and once both divers caught their breath the hoses could be swapped if it was more convenient before starting our ascent. I'm really keen to hear real life situations where a manifold has been a significant advantage.

3) I'll never opt out of spending cash on safety and would buy a manifold tomorrow if I believed it offered significant safety aspects - but as I don't see the benefit, I'm opting to keep my pennys.

(Although - I best confirm that by cheap I mean saving money, and not poor quality gear). I've heard that cheap in some countries is used to describe goods as inferior instead of just better priced. I'm not that sort of cheapskate. :smiley2:

I really do want to understand, but are sometimes suspicious that some of the benefits that are put to one method over another are more theoretical than have ever been practiced?

Once again - thanks for your reply. I stress that my intentions aren't to argue facts and methods but to really understand the benefits of manifolds. I may be a bit thick in the head which is why I'm detailed (and honest) in my replies - hoping that someone can help me understand the other points of view. So please take my replies as been inquisitive and not argumentative.

Cheers

in_cavediver
06-16-2009, 05:53
Basically, from my perspective, you need to look at stats as well as scenarios

I have yet to hear about a manifold failure leading to total gas loss. It is possible but seems to be extremely rare. Given that, the advantage of accessing all of your gas from either reg is very appealing.

Still, independents lack that issue though you get at most 1/2 of your gas with a failure. It also adds task loading. It may not seem like much but it can be, especially for a newer diver. If you add in the refinements to the isolated doubles setup vs independents you start to see more advantages for new divers (to this config). My side mount rig is semi-custom to me. Anyone could dive my backmount rig.

Me - I dive both configurations. I like the simplicity of doubles in the water but I like the separateness of side mounts out of the water. I can do either.

Roughwater
06-16-2009, 06:33
Hi Incaver,

Thank you very much for your reply!

It would appear as though your post reflects what Compudude has said too. That being the case, I have covered the main benefit for Manifolds in points 1a and 1d in my prior post.

So - I guess I'm not actually 'missing' anything, (I was successful at having a womans look before posting :smiley36:) .

I suppose the reason why I've been confused or thought that I was missing something was because I don't see those two points as a big issue where others do, and I see other points (such as 2a, 2c, 2d and 2e outweighing the benefits of 1a and 1d). Which of course is personal choice, and related to the types of dives I do. - that it comes down to personal choice, experience and what one is comfortable with.

I would be interested to know the stats too, for as with my own personal experience, I have noiced divers with manifolds having more problems than those without. (Of course this is restricted to only those I have personally observed), and wonder if the stats reflect otherwise.

Lastly - if anyone else has something else to add that I've missed in my points, please reply. I'd like to add to the list to cover everything and not miss anything if possible.

I have seen this topic as very heated discussions on other boards and mailing lists by people with very passionate mindsets, and really didn't want to get into a mud slinging name calling session - which is why I thought ST was the best place to ask. :smiley2:

I really can't express how much I appreciate both of you replying to try and help me understand.

Cheers

Roughwater
06-16-2009, 06:34
On a seperate note, I was thinking - my main concerns have to do with emergency situation and reaction time - and maybe there's a way of getting the best of both worlds. (Have my cake and eat it too).

For instance, if I set up manifolds, but kept the isolation valve turned off for normal dives, I then eliminate the concerns of 2b (reaction time) and 2e (simultaneous running out of air) which are my main two safety concerns. I could then still isolate the purging reg, and then turn on the isolation valve, to still give the benefits of both cylinders (1a). This to me seems to be the safest way to operate manifolds.

Is this an accepted method of manifold setups? Does anyone see a problem with this?

Cheers

UCFKnightDiver
06-16-2009, 08:43
That valve/manifold configuration is not often used I have heard of maybe two people using it in the configuration you suggested

LiteHedded
06-16-2009, 09:00
isolation manifolds just don't fail.
it doesn't happen. and if it does you have sufficient reserves on your buddy's back to get you home. I don't see the problem

RoyN
06-16-2009, 17:18
I wouldn't use independant doubles because I need the manifold to shutdown the left tank if something happens.

in_cavediver
06-16-2009, 17:20
isolation manifolds just don't fail.
it doesn't happen. and if it does you have sufficient reserves on your buddy's back to get you home. I don't see the problem

Ah but this too has faults. What happens in a restriction where going to an air share is a PIA. What about solo (or team solo diving like some sidemount dives). There are cases to be made for adding the complexity of independents. There are logistical constraints that may cause independents to be the optimal or only choice.

It's all a trade off and each diver needs to make an informed decision based on 1) the dive 2) their skills and 3) the risks. There is no right or wrong answer. Sometime independents are better, sometimes manifolded doubles are better. This is truely situation dependent.

Still, I strongly believe entry level tec divers would do themselves a favor by starting with the tried and true universal hog rig. Once they build up expierence, they may find situations that may cause independents to be a good tool to add to the arsenal.

in_cavediver
06-16-2009, 17:22
I wouldn't use independant doubles because I need the manifold to shutdown the left tank if something happens.

With independent doubles - think two standard tanks - no crossbar, no extra outlets, just two standard tanks. (could be backmount or sidemount). In the case of a failure, you simply shut down the valve on the bad tank. With sidemount, its literally right in front of you so its not hard to ID the problem.

Roughwater
06-16-2009, 17:31
isolation manifolds just don't fail.
it doesn't happen. and if it does you have sufficient reserves on your buddy's back to get you home. I don't see the problem

Hi LiteHedded,

I agree, manifolds may not fail, but people do. I've seen people dive with manifolds who cannot for the life of them reach the isolating posts, or one of the other posts - yet they still insist that manifolds are the way to go.

Don't get me wrong - I think the isolation manifold is a great invention and certainly have their place - I'm just trying to understand other peoples different view points. (Some are easier to understand than others. :smiley2: )

Thanks for the reply!

Cheers

RoyN
06-16-2009, 17:39
There is alot of people who cannot reach the manifold because of out of shape or bad arms. This was one of the problems I had to overcome when I began my path to tech diving. My tech instructor said this is the one problem that many tech divers failed in. But unlike some tech teachers that simply fail, he tries and helps the diver overcome this problem.

MSilvia
06-16-2009, 17:47
There is alot of people who cannot reach the manifold because of out of shape or bad arms.
I don't at all mean to dispute that, but there are also a lot of people who can't reach them because of incorrect gear configuration or poor technique, and they often blame bad flexibility instead of (for example) an ill-fitting drysuit undergarment or elbow jutting out to the side instead of the front. If you can touch your back between your shoulder blades, your physical condition isn't the issue.

Roughwater
06-16-2009, 18:05
That valve/manifold configuration is not often used I have heard of maybe two people using it in the configuration you suggested

Thanks for your reply. Just wondering if there is a reason behind this. With my way of thinking this would seem to be the safest option and the best of both worlds and I was wondering what I've missed (if it's not a more common approach).

MSilvia
06-16-2009, 18:25
Thanks for your reply. Just wondering if there is a reason behind this. With my way of thinking this would seem to be the safest option and the best of both worlds and I was wondering what I've missed (if it's not a more common approach).
I like that you're really thinking about the problem, and you raise an interesting point. Personally, I prefer to limit my task loading by not having to balancing the gas in my cylinders, but if that's not a concern... well, I'll have to think about it. To be honest, I'm not sure what you're missing, if anything other than actual experience with doubles.

Roughwater
06-16-2009, 18:43
Hi Matt,

Thanks for your reply. I've been diving independent doubles for a few years now and have only recently tried manifolds (a friends setup). Maybe it's that I'm more familiar and comfortable with the independents that's causing me to be biased?

ie - take away the concern of swapping regs / evenly decantering as being an issue (as it's not with me) and the fact we dive to 3rds and most of the benefits of a manifold (that's been expressed here) seems to lessen in weight while the concerns remain the same.

Hope you guys don't mind, but I have two more questions to throw at you:

Question 1:

In regards to what we've been talking about - would I be correct in summarising that the only reason not to have the isolation valve turned off during normal dives is the even decanter (not having to swap regs), and this is considered more of a task load or concern to most than being able to reach and turn off the isolation valve in time to save most of the air supply? (Or is there another reason not yet specified)?

Question 2:

There are 2 other ways that I can see to operate a manifold apart from my suggestion above:

(a) To have the isolation manifold turned all the way on, and turn it off when required, and

(b) To have the isolation manifold cracked open a little, so it only requires 1/2 a turn or so to isolate the tanks - thus speeding up the process and reducing the risk of air loss.

Just wondering which of these ways is the most recommended / popular and why too please?

Once again - thanks for all your replies and inputs. I'm learning. (Even if it is slowly) :smiley2:

RoyN
06-16-2009, 19:01
I don't at all mean to dispute that, but there are also a lot of people who can't reach them because of incorrect gear configuration or poor technique, and they often blame bad flexibility instead of (for example) an ill-fitting drysuit undergarment or elbow jutting out to the side instead of the front. If you can touch your back between your shoulder blades, your physical condition isn't the issue.

I cannot dispute that either, but the tech instructor is going to help the students one way or another before officially saying he can't certify them because of that. Seriously, I couldn't reach the left side, but I tried, found another way, and manage to shut it off in a small amount of time.

UCFKnightDiver
06-16-2009, 19:32
In question one by saying "the isolator off" do you mean open or closed

The most popular way is having the isolator all the way open, in the not so distant past there has been deaths due to the isolator valve being closed and the diver not realizing, they breathed their right tank down while their guage was still reading at the starting pressure... he died (he was also diving abover his level) of course I suppose if you knew your iso was closed this wouldnt be a problem. I think your suggestion of diving the isolator cracked or closed has merrit but if solo diving I would just recommend side mount its the best tool for the job! if you do have a reg free flow it seems that it would be not at all hard to manipulate and then feather your valve to breath in a sidemount configuration. Independent backmount cylinders in my opinion just arnt ideal. Nor are Manifolded doubles. If you want to be a "cheapskate" and dive single tanks and "doubles" with minimum hassel sidemount is the way to go as well.

Roughwater
06-16-2009, 19:44
In question one by saying "the isolator off" do you mean open or closed


Just to confirm, I mean closed. (So they are technically independent tanks, but if a failure occurs one can isolated the faulty post and then open the isolation valve to access the additional air).



The most popular way is having the isolator all the way open, in the not so distant past there has been deaths due to the isolator valve being closed and the diver not realizing, they breathed their right tank down while their guage was still reading at the starting pressure... he died

That's a sad event. If his isolator valve was closed, couldn't he have just switched to his other reg? (Although I guess it's easy to evaluate here sitting in my office, rather than an OOA situation at depth)

UCFKnightDiver
06-16-2009, 19:45
yes he could have switched regs but instead he switched to his o2 bottle at around 60 ft.

ianr33
06-16-2009, 20:09
If you want to be a "cheapskate" and dive single tanks and "doubles" with minimum hassel sidemount is the way to go as well.

A sidemount harness,new hoses and another spg is not exactly "cheap" !!

UCFKnightDiver
06-16-2009, 23:16
you missed my point entirely "doubles" as in 2 tanks like sidemount tanks are able to be used as single tanks with out much if any modification

navyhmc
06-16-2009, 23:44
In question one by saying "the isolator off" do you mean open or closed


Just to confirm, I mean closed. (So they are technically independent tanks, but if a failure occurs one can isolated the faulty post and then open the isolation valve to access the additional air).



The most popular way is having the isolator all the way open, in the not so distant past there has been deaths due to the isolator valve being closed and the diver not realizing, they breathed their right tank down while their guage was still reading at the starting pressure... he died

That's a sad event. If his isolator valve was closed, couldn't he have just switched to his other reg? (Although I guess it's easy to evaluate here sitting in my office, rather than an OOA situation at depth)

The best case that can come from an event such as that is to be aware of which way the isolator is when you start the dive. I can understand how that can occur, but at the same time, If I'm down10-15 minutes at even moderately shallow depths and notice that there is not a drop in the PSI even a small drop, I will consider the isolator closed.

A couple of questions that arise from that scenario:

If I had intended the isolator to be open and have determined that it's closed let's say 10 minutes into a 110' dive, do I just go ahead and open it, allowing the tanks to equalize?

If I do indeed open the isolator and the tanks equalize, will I have to worry about the temperature changes and could that cause problems given that one tank and one side of the manifold is getting cooler and the other side is getting warmer, could this cause a manifold failure?

I've never thought about that before.

Roughwater
06-16-2009, 23:51
Hi Navyhmc,

Good questions. I know little about that, so I won't comment.

However on what's been said, am I right in guessing that a standard manifold setup has the SPG coming off one post and the normal breathing reg coming off the opposite post?

If so - is there any particular reason having it this way (as I can see that this could lead to a serious problem as stated before if the isolator is closed, and the SPG shows the same gas throughout the dive)?

navyhmc
06-17-2009, 02:50
Hi Navyhmc,

Good questions. I know little about that, so I won't comment.

However on what's been said, am I right in guessing that a standard manifold setup has the SPG coming off one post and the normal breathing reg coming off the opposite post?

If so - is there any particular reason having it this way (as I can see that this could lead to a serious problem as stated before if the isolator is closed, and the SPG shows the same gas throughout the dive)?

I too am faily new to doubles-in the modern isolator w/two posts sense-the last double I used were twin 80's w/a single regulator. The standard tech set up is a first stage w/single second stage on each post (usually DIN) the right first stage also provides the lp hose for the BCD/Wing, the left post has the SPG. The idea for Tech is that the isolator is open all the time and is only closed when there is a leak on either side of the isolator so there is at least on cylinder that the diver can breath off of that is not free-flowing. Both posts can also be shut off independantly in the case of a regulator failure. In this case, the tank on the effected side can still have the gas in it available for use.

Also of note, if you do have an isolator problem, you still breath off the effect side until that cylinder is empty. Of course, in the case of any failure, the dive is turned and returning safely to the surface is now the mission of the team.

As noted, in the normal diving with doubles, the isolator is intended to be open, only closed in an emergency. I have done solo dives where I have used doubles as independant cylinders as a redundant gas system. In that case, I know ahead of time that the isolator is closed and if I need to use the left tank, the dive is over and I'm headed to the surface. I don't do overhead environments or deco when solo (Not thtat I do deco dives anyway.) so all I am concerned about is my safety stop and I have plenty of gas for that. I also have a SPG for both tanks when I run them as independants.

Clear as mud?

MSilvia
06-17-2009, 10:33
However on what's been said, am I right in guessing that a standard manifold setup has the SPG coming off one post and the normal breathing reg coming off the opposite post?

If so - is there any particular reason having it this way (as I can see that this could lead to a serious problem as stated before if the isolator is closed, and the SPG shows the same gas throughout the dive)?
Typically, manifolded doubles have a single SPG on the same post as the primary breathing reg. The thinking is that that gauge will read the combined pressure in both tanks with the isolator open. Since the isolator (typically) would only be closed in the event of an emergency causing gas loss from one cylinder, the quantity of gas remaining becomes more or less irrelevant when the isolator is closed... you're aborting the dive at that point regardless of what the SPG would read.

UCFKnightDiver
06-17-2009, 10:36
I believe the Typical setup as Ive seen it at least is to have the spg on the left post as well as your backup regulator, with the primary regulator and inflator hose on the right post

MSilvia
06-17-2009, 10:51
I believe the Typical setup as Ive seen it at least is to have the spg on the left post as well as your backup regulator, with the primary regulator and inflator hose on the right post
You're right... my mistake.

ianr33
06-17-2009, 13:05
[quote=Roughwater;306529

If so - is there any particular reason having it this way (as I can see that this could lead to a serious problem as stated before if the isolator is closed, and the SPG shows the same gas throughout the dive)?[/quote]

If the pressure on the spg is not dropping then that is a HUGE red flag that the isolator is closed.
You can open the isolator and listen to the pressures equalizing(and see the spg drop)
However,if the isolator is found to be closed during a dive maybe it was also closed when the tanks were filled? In which case what the hell are you now breathing?

DivingCRNA
06-17-2009, 14:08
when you dive side mount tank you don't use a manifold so why not aply the same priciples of diving side mounts as back mount doubles?

I heard someone made a side mount manifold and there is a pic on the net. It is huge and weird.

LiteHedded
06-18-2009, 07:33
manifolding the tanks defeats the purpose of sidemount.
being able to remove a tank if you get stuck is a big benefit

DivingCRNA
06-18-2009, 07:34
manifolding the tanks defeats the purpose of sidemount.
being able to remove a tank if you get stuck is a big benefit

I never said it was a good idea.... I just saw it.:smiley2:

in_cavediver
06-18-2009, 11:51
If so - is there any particular reason having it this way (as I can see that this could lead to a serious problem as stated before if the isolator is closed, and the SPG shows the same gas throughout the dive)?

If the pressure on the spg is not dropping then that is a HUGE red flag that the isolator is closed.
You can open the isolator and listen to the pressures equalizing(and see the spg drop)
However,if the isolator is found to be closed during a dive maybe it was also closed when the tanks were filled? In which case what the hell are you now breathing?

Another part to this is to catch roll-offs. This is where the left post turns itself off during the dive due to contact with the ceiling. If you notice the pressure not dropping like it should - you may have a closed isolator or a rolled off post. Both are nice to know before you need them.

CWSWine
06-18-2009, 12:55
I dove last weekend with a cave dive instructor, side mount instructor and he is on the west coast anti terrorism dive team and we just did some simple open water diving. Needless to say that was a real eye opener for new me a new OW diver and I learned a lot. We discussed me going to side mounted 72ís or possibility something even smaller later this year or next year. I have a back that is just getting worse by the year and going side mount would lessen strain and possibility extend my years of diving. Putting the tanks in the water and mounting them after getting in would lessen the strain during entry. He was saying the medical issues was making side mounting more main stream - from backs, knees and the handicap divers are starting see the advantage of side mounts.