Double Tank Manifolds, Bad Idea!

[tskovan]

Please name three
[/SIZE][/FONT][/COLOR]



OK

I’ve been ignoring you because apparently your attitude is; manifolds (like yourself) are infallible! One just has to read your post quote: "You may not agree with everything I say but at the very least you'll come to understand that your differing opinion is wrong"

If that’s the case, what do we have to talk about? But you keep trying so I’ll give you the benefit of the doubt that the quote is a joke.


Here’s a few, pick your favorite three

1. Tank o-ring
2. first stage failure
3. burst disk
4. valve failure
5. manifold failure
6. tank failure
7. improperly filled(wrong gas, closed isolation valve)

Now some of these can be dealt with if properly diagnosed and the proper corrective action is taken quickly enough, and some can’t. My point is with IDs I just switch regulators, and go home, done. “KISS”

I’ve been repairing mechanical systems my whole life, if you think a system with multiple threads, multiple o-rings and three valve assembles, that require proper assemble, alignment and maintenance CAN’T FAIL your fooling yourself. Manifolds, like all mechanical things, can and do fail, probably a lot more often than people think, but you won’t here about it unless someone is injured and it gets reported (people generally don’t advertize stupid mistakes if they don’t have to). Don’t get me wrong, I’m not saying manifolds are unreliable, I know there are very reliable and failures are rare, as I said in my OP! But they do happen.

 

[Ste Wart]

Here’s a few, pick your favorite three

1. Tank o-ring

​
Same for IDs​

first stage failure

Same for IDs


​

burst disk

Dependent on Valve, relevant to IDs

valve failure

Same for IDs

manifold failure

Team Mate has available gas

tank failure

Same for IDs

improperly filled(wrong gas, closed isolation valve)

Why would you not analyse?

There is no argument here

 

[DevonDiver]

My point is with IDs I just switch regulators, and go home, done. “KISS”.

Firstly; you do make it sound very simple. My concern is that the simplicity with you view the use of independent tanks probably stems from a background of very benign diving. There are issues involved with confined area/overhead environment diving, or when completing complex tasks, or when using other equipment, that make regulator exchanges and/or cylinder balancing and/or maintaining a proper gas distribution plan a considerable task loading, especially for those without highly ingrained equipment familiarity. As task/dive complexity increases, you may find there is little "KISS" about just switching regulators.

That isn't to say that the reg-switches are more dangerous, or cannot be mastered under any level of competing demand, but the approach is of considerably more task-loading than diving with a manifold. For less experienced divers, or those unused to independent tanks, that should be a significant consideration.

For ten years I dove both manifolded and independent doubles. I used independent configuration for more remote travelling where bands/manifolds/valves were not available - simply cam-banding regular AL80s to my rig (Custom Divers TDB: a good rig, it accepts 4x cam bands and holds indies securely). Then I moved to sidemount config, which is also an independent cylinder system (eschewing the awful Z-manifold), but uses a more frequent reg-switching protocol. When it comes to the other advantages offered by sidemount, I think that going 'indie' is an acceptable option.

Secondly; it is important to consider other factors applicable to indies versus manifolds. For instance, if sharing gas. With a manifold system you can ensure the receiver always goes for the regulator in your mouth. When diving indies, you have more issues to confront, because your regulators (one short, one long?) will be in/out of your mouth throughout the dive. The common principle of 'donate from the mouth' gets scuppered. That may not be critical, but added complexity does degrade and slow emergency protocols. In low/zero-viz and/or confined/overhead environments, any confusion or delay could prove costly. Again, application of good protocols, effective training and rehearsal go a long way to nullify this... but the margin for error remains...and is increased in proportion to the inexperience or unfamiliarity of the diver/s concerned.

 

[AfterDark]

Interesting debate, this was my first post on SB, (don’t think I deserved all the “Troll” accusations), I stand by my OP and believe that, for non-cave diving, IDs are a better choice especially when solo diving. To those who said that the valves are in the same place whether using a manifold or IDs, your missing one of the most important points of using IDs. Using the rule of thirds while diving, I always have enough gas in either tank to—in the event of a failure, ANY TYPE OF TANK OR REGULATOR FAILURE—simply switch regulators, turn the dive, and go home! It doesn’t get any easier than that, there is no need to reach for valves, ever. During the added stress of a failure simpler is better IMO, the added task loading of gas management is done easily in a non-stressed manor throughout the dive, and the true TOTAL redundancy IDs give is very comforting when solo diving (which I do almost exclusively).
Also I have my own boat and do a lot of diving at slightly remote lakes in AZ. I bring 6 or 7 tanks with me for a week end, after a dive I slide the empties out of my bands and slide in two full tanks, you can’t do that with a manifold.
Thanks to everyone who replied intelligently.

Sounds like you have it down pat. I don't use thirds, I know how much gas I'll use and how much I'll need to get back. My choice of tank size is based on calculations for a given dive. Short shallow dives I use my 50's deeper non-deco dives my 72's, deep dives with short deco times a set of 94's. This works for me and has kept me alive and with ample air for hundreds of dives. The only change in config. I make is when diving with a buddy. I add a slung pony bottle for my buddy. In a OOG situation I'll hand the bottle off. When solo the pony stays home. My back gas is for me. One more thing I do, my alt. LP hose is protected so if its needed it's clean.

 

[mathauck0814]

I dive a longhose/bungied B/U with ID's. The hose configuration is exactly the same as MD's except I have one more SPG on the right post. As to clutter, to even things out the MD diver has an extra valve to contend with.

So you have two regs bungeed around your neck and two long hoses wrapped? Or you have a single second stage on each of your independent posts? I can see the latter more than the former (again, for clutter). The comment about the third valve seems valid - you do have one more to manage and one more failure point, but on ID you're going to be dealing with a valve behind your head and a regulator switch where on MD you're going to be dealing with at least one and maybe two valves and maybe a regulator switch.

I don't really have a dog in the race as I rarely dive OC anymore, but I'm not seeing the simplicity. Seems like there's just as much stuff to contend with and you don't get the full use of your available gas.

Obviously, like many, I was trained with manifolded doubles and thus it's more comfortable so I'm probably just biased by what I know.

 

[DaleC]

Gabe, I've never said ID's were superior to MD's - that's the other guy. I was just explaining why I prefer them. As you say, a personal choice. When it comes to redundant systems I simply feel separate is better (for me). It's a mental approach to risk mitigation that I feel comfortable with. If I were seeing action in a sub I would probably want the water tight doors dogged down before the torpedo hit, not after.

As to further training so we can do that boat; it all comes down to one thing:

Money baby... Money

I also recognize that the more "technical" one gets, the fewer options one has for risk mitigation. That is why I agree that for dives where max usable air is required, MD's are a better choice. My type of diving is not really that "technical" by nature but that is where SB has put the solo section and where this thread is, so?? If the title were ID's are better for cave/penetration/mixed gas/deep diving I think I would answer differently. I don't hold with the OP's us vs them posturing. To me, choices like this have too many variables.

 

[AfterDark]

So you have two regs bungeed around your neck and two long hoses wrapped? Or you have a single second stage on each of your independent posts? I can see the latter more than the former (again, for clutter). The comment about the third valve seems valid - you do have one more to manage and one more failure point, but on ID you're going to be dealing with a valve behind your head and a regulator switch where on MD you're going to be dealing with at least one and maybe two valves and maybe a regulator switch.

I don't really have a dog in the race as I rarely dive OC anymore, but I'm not seeing the simplicity. Seems like there's just as much stuff to contend with and you don't get the full use of your available gas.

Obviously, like many, I was trained with manifolded doubles and thus it's more comfortable so I'm probably just biased by what I know.

If a disk failure should happen on a MD tank the diver would have about as much available gas as the diver using ID's, depending how fast the MD diver reacts. Seems as likely as any other type failure, which is not very.

 

[Slamfire]

Small point, but 'stages' are typically bottom gas. Stages and deco tanks being separate things, by definition.

Point taken. My reply was still under the context of the Gunilda dive and I didn't want to expand an already verbose reply by explaining semantics.

Which explains the above.

Under the context of the Gunilda, a four gas deco dive, I would like to avoid taking a stage if I can. One less tank is a welcome reduction in complexity. I would prefer to keep this a 4 gas dive and not make it a 3 gas dive because I can shave off some minutes from deco time. I realized later that nowhere in my posts did I ever specify that all slinged bottles were to carry deco gas. Readers could have easily assumed that one of those Al80s was a stage.

 

[Tortuga68]

Hey guys, sorry to interrupt the sidemount lovefest but...

I’ve been ignoring you

Well gee, thanks for taking the time to respond to my question which you invited in your OP

because apparently your attitude is; manifolds (like yourself) are infallible!

No idea where you got that from, or even why you brought it up. You said there are "any number" of failures which lose all your gas, I merely asked you to name three. Seems like a resonable question.

One just has to read your post quote:

"You may not agree with everything I say but at the very least you'll come to understand that your differing opinion is wrong" If that’s the case, what do we have to talk about? But you keep trying so I’ll give you the benefit of the doubt that the quote is a joke

How generous, just like I gave you the benefit that your OP wasn't a troll. Funny that you complained about people judging you

Treat yourself to this: Amazon.com: I Am America (And So Can You!) eBook: Stephen Colbert: Kindle Store

Here’s a few, pick your favorite three

1. Tank o-ring
2. first stage failure
3. burst disk
4. valve failure
5. manifold failure
6. tank failure

Yes, any of those failures "can loose you all your back gas" if you don't do anything about it. My mistake, I thought we were talking about scenarios where the diver actually had some influence on their equipment.

So in summary, I totally agree with you; you shouldn't dive manifolded doubles if you're incapable of closing the isolation valve/posts since that defeats the purpose of having a manual valve anyway.

I have come to that conclusion because the only other scenario that makes sense is that you don't actually know how an isolation manifold works

 

[nimoh]

If a disk failure should happen on a MD tank the diver would have about as much available gas as the diver using ID's, depending how fast the MD diver reacts. Seems as likely as any other type failure, which is not very.

Might be worth noting that in the time it takes to close the isolator, the diver is losing gas from both sides which is not the case with ID.

However, I am still not convinced that a disk failure or tank neck o-ring are common enough problems to forgo the advantages of the isolator with respect to outboard problems.