Double Tank Manifolds, Bad Idea!

[tskovan]

I’m not sure who came up with the doubles manifold and then the isolation manifold but nether one is a good idea. Now I know this may sound a bit sacrilegious to many of you, but here me out.
First let me say that I’m not a cave diver, cave diving takes on a level of risk that I’m not willing to accept—just look at the fatality statistics for cave divers. I’m not against cave diving, it’s just not for me.
That being said, the only credible argument for tank manifolds is: if you’re far in an overhead environment and you have some type of failure you can shut down one post and still have access to the gas in both tanks to get back out. Now, if you’re so far in an overhead environment you can’t get back out on one tank, you have made an error in pre-dive planning not equipment configuration. So that’s the argument for using a manifold, what’s the argument against? Well here’s a short list:
· You wear two tanks for basically two reasons, longer bottom time and redundancy. Longer bottom time is a luxury, lack of redundancy can Kill you! Once you connect those two tanks together with a manifold you no longer have redundancy, you have essentially made one big tank! Any number of failures (all though rare) can loose you all your back gas.

· You have just installed a complicated life support system behind your back! These valves are difficult to reach (at best) and impossible to see, sure, it can be done (valve drills and all) but that doesn’t mean it’s a good idea. Fumbling with valves behind my head at depth in a stressful, life threatening situation is not inconvenient it’s dangerous and unnecessary.
· Then there’s the issue of having the valves in the right configuration when the tanks are being filled, another unnecessary complication.
· Manifold doubles are very heavy and awkward to deal with out of the water.
· You must dedicate the same two tanks to your rig.

I dive independent twins, that’s two tanks with a first and second stage on each tank and nothing connecting them together. My valve drills consist of turning them on before I dive and forgetting about them. I have my right regulator on my right tank clipped to my D-ring and my left on a necklace, I use a Hog switchback Regulator on the left with the hose coming off the left side, this way there is never any confusion as to which tank I'm using. This set up suffers none of the problems of manifold doubles and has many advantages. The drawbacks of independent twins usually mentioned are:· You have to switch regulators during the dive (which only takes a few seconds and confirms that both regulators are functioning properly through out the dive, not really a draw back).
· You need two submersible pressure gauges (SPG’s) and must monitor them to switch at the proper time.

First of all, shouldn’t you have two SPG’s on manifold doubles? What if you have to shut down the post with the gauge on it?(I’ve always been amazed that DIR set-ups use only one SPG) and if your at the level of diving that your wearing two tanks, shouldn’t checking your gas supply be like checking your side view mirror before changing lanes on the highway, you do it often without even thinking about! If not maybe you should rethink diving at advanced levels.
The convenience of independent twins over manifold doubles can’t be over stated, I loosen two nuts and slide the tanks out of the bands, I can mix and match tanks anyway I need to (provided there the same diameter). Often I will put a half full tank (left over from a previous dive) with a full one and have plenty of gas for a great dive. Filling them is also straight forward and easy. I dive mostly Solo, Tech, Low Vis and some Wreck penetration.
Manifolds have become the standard in tech diving, but if you really think about it, as I have, Manifolds don’t make a lot of sense, I will never use one.
Thoughtful disagreement is always welcome.

 

[Ste Wart]

So that’s the argument for using a manifold, what’s the argument against? Well here’s a short list:
· You wear two tanks for basically two reasons, longer bottom time and redundancy. Longer bottom time is a luxury, lack of redundancy can Kill you! Once you connect those two tanks together with a manifold you no longer have redundancy, you have essentially made one big tank! Any number of failures (all though rare) can loose you all your back gas.

Accepted risk. However as you said it is very, very rare.

· You have just installed a complicated life support system behind your back! These valves are difficult to reach (at best) and impossible to see, sure, it can be done (valve drills and all) but that doesn’t mean it’s a good idea. Fumbling with valves behind my head at depth in a stressful, life threatening situation is not inconvenient it’s dangerous and unnecessary.

I don't see how the valves are in a different position when diving independents, unless you mean sidemount.

If I can't reach my valves; unlikely. I can't identify the faulty valve, possible. Then my buddy will help me shut them down. Either way he/she has a gas source I can use.

· Then there’s the issue of having the valves in the right configuration when the tanks are being filled, another unnecessary complication.

Having the isolator open? Not hard

· Manifold doubles are very heavy and awkward to deal with out of the water.

As are independents.

· You must dedicate the same two tanks to your rig.

Indeed, I call mine, a twinset.

First of all, shouldn’t you have two SPG’s on manifold doubles? What if you have to shut down the post with the gauge on it?(I’ve always been amazed that DIR set-ups use only one SPG) and if your at the level of diving that your wearing two tanks, shouldn’t checking your gas supply be like checking your side view mirror before changing lanes on the highway, you do it often without even thinking about! If not maybe you should rethink diving at advanced levels.

Non-issue. As long as I haven't violated min gas I can get to the surface without needing to look at a gauge

 

[Dr. Lecter]

I here that obvious trolls are obvious, and loosing them can be as easy as ignoring them.

 

[eelnoraa]

Assuming you are not trolling, I think my training is so fundamentally different than yours, that I don't even know how to start my disagreement.

First of all, shouldn’t you have two SPG’s on manifold doubles? What if you have to shut down the post with the gauge on it?(I’ve always been amazed that DIR set-ups use only one SPG) and if your at the level of diving that your wearing two tanks, shouldn’t checking your gas supply be like checking your side view mirror before changing lanes on the highway, you do it often without even thinking about! If not maybe you should rethink diving at advanced levels.
The convenience of independent twins over manifold doubles can’t be over stated, I loosen two nuts and slide the tanks out of the bands, I can mix and match tanks anyway I need to (provided there the same diameter). Often I will put a half full tank (left over from a previous dive) with a full one and have plenty of gas for a great dive. Filling them is also straight forward and easy. I dive mostly Solo, Tech, Low Vis and some Wreck penetration.
Manifolds have become the standard in tech diving, but if you really think about it, as I have, Manifolds don’t make a lot of sense, I will never use one.
Thoughtful disagreement is always welcome.

As for DIR diver using one SPG for double, here is a short explaination. In the very first entry level class we take, we are taught to keep track of our gas in our brain based on very simple physics, + knowing our equipments, knowing yourself and environmental awareness. In another word, our brain is the main "SPG". And we check actual SPG periodically to confirm our calculation. If the SPG reading is too far from our calculation, we know something is not normal. It is time to identify and maybe fix the abnormalies. With some training, it is surprisingly easy. And actually, we don't look at the SPG as often as we would look at rear view mirror while driving.

 

[Peter69_56]

I understand your feelings however I do disagree with your conclusions. I do dive both doubles and twin independents. I have one set of twins and 2 singles. Both have their good and bad points. I agree that ideally it would be good to have 2 SPG but the idea is to abort if you lose one reg set and you are supposed to have sufficient in reserve. Also you have your buddy or biddies supplies as well. The down side of 2 SPG is extra gear which can cause drag and entanglement etc. If you cant reach your twin valves maybe single independents are for you, if you can like I can then why write off twins?

In the end I believe you dive how you are comfortable but ensuring your buddy knows your rig. Non is right or wrong (generally speaking although some is just plain bad). My personal view is all systems have their good and bad, non are so bad one shouldn't use them. Just recognise the good and bad and use what you are comfortable with. Your post seems to indicate the twins are just bad, and that's what I would disagree with.

Oh you forgot one extra thing that's a down for twins, to get them tested costs more than twin independents as they now can charge for disassembly/assembly.

Anyway I use and am ok with both setups. Each is good for their circumstance.

 

[pocky21]

Don't worry guys, this is pretty typical for Tucson - too much Vitamin D

All kidding aside, I don't think this is a troll post. To the OP - you have some valid concerns, but a little research goes a long way. I know the diving community in Tucson is just as sheltered as it is opinionated (been there, done that), but please don't expect the warmest of welcomes with the approach you have taken to discuss what is now considered a standardized equipment configuration. Others with far more experience and knowledge than I already have, and will, attempt to educate you as to why it has become the standard - but a "better than thou" approach will get you nowhere here.

By the way, welcome to scubaboard!

 

[Tortuga68]

Once you connect those two tanks together with a manifold you no longer have redundancy, you have essentially made one big tank! Any number of failures (all though rare) can loose you all your back gas

Please name three

Manifolds don’t make a lot of sense, I will never use one

OK

 

[tskovan]

Thanks for the welcome pocky21, (actually my vitamin D is low, I have to take supplements):cool2: and thanks to all who replied. Sorry if my post came off sounding “better than thou” It was not my intent. You said a little research goes a long way, and I agree. I think I’ve done quit a bit of research on this issue and have come to the conclusion I laid out in my original post. And I respect the opinion of those who disagree with me, but your post, I think really makes my point, as you said “to discuss what is now considered a standardized equipment configuration”. All I’m asking is why is it “now considered a standardized equipment configuration”. Everyone defends it by basically saying it’s manageable, not by explaining why it’s better. Even you said “Others with far more experience and knowledge than I already have”. I guess I’m posing my question to them.

I considered for a long time weather to use a manifold, and searched SB relentlessly for a good reason to do so, I just never found one, I’m sorry but the “that’s just the way it’s done” argument doesn’t sway me.

I’m sounding “better than thou” again aren’t I…………… sorry.

 

[ajduplessis]

Great way to start your first post :sarcasm: Let's for a moment take the troll bit out of the equation and give you the benefit of the doubt.

I’m not sure who came up with the doubles manifold and then the isolation manifold but nether one is a good idea. Now I know this may sound a bit sacrilegious to many of you, but here me out.
First let me say that I’m not a cave diver, cave diving takes on a level of risk that I’m not willing to accept—just look at the fatality statistics for cave divers. .....

Can you please cite the statistics you refer to around cave diver fatalities because you clearly don't know what you are talking about. Dive fatalities amongst certified cavers is very low.

Once you connect those two tanks together with a manifold you no longer have redundancy, you have essentially made one big tank! Any number of failures (all though rare) can loose you all your back gas.

Thank you for clearing up any confusions members might have had over your understanding of redundancy. We can now confirm it is 0% . Once you close the isolator you have 2 completely separate/independent systems.

These valves are difficult to reach (at best) and impossible to see, sure, it can be done (valve drills and all) but that doesn’t mean it’s a good idea. Fumbling with valves behind my head at depth in a stressful, life threatening situation is not inconvenient it’s dangerous and unnecessary.
· Then there’s the issue of having the valves in the right configuration when the tanks are being filled, another unnecessary complication.
· Manifold doubles are very heavy and awkward to deal with out of the water.
· You must dedicate the same two tanks to your rig.

If you can't reach the valve then don't dive them. Simple as that and then rather go sidemount.

If you have the urge to see your valves use a reflector/mirror. If you need to see what you are doing then don't dive at all. Silt and bad vis can happen on any dive which brings me to the next point. How do you read your gauges, see your valves on a silt-out wreck penetration? You only fumble and get stressed if you don't know what you are doing. Example: If you feel there is an unnecessary complication in opening a valve to get them filled, then I suggest someone show you how to open an close a valves, it’s really easy and they all work the same way. Left is open and you will not believe me but right closes them. If you find doubles heavy and awkward to handle above the water you might want to ask some of our ladies divers here what they eat for breakfast.

First of all, shouldn’t you have two SPG’s on manifold doubles? What if you have to shut down the post with the gauge on it?(I’ve always been amazed that DIR set-ups use only one SPG) and if your at the level of diving that your wearing two tanks, shouldn’t checking your gas supply be like checking your side view mirror before changing lanes on the highway....

You check you gas supply during the dive and therefore you will turn the dive at the correct pressures. Therefore, should you shut down a post at any point during a dive you know you have the gas to get out because you followed a dive/gas plan and checked you gauges during the dive. You have terminated the dive, get out. PS: You can check your side view mirror without changing lanes, its called situational awareness. It's almost the same as checking your gauges during a dive. I really struggle to see that you have any form of training even though you say you participate in tech/solo/wreck diving.

Often I will put a half full tank (left over from a previous dive) with a full one and have plenty of gas for a great dive.

Until the full cylinders fails and you only have a half empty left to complete your GREAT dive. I now understand why you refer to fumbling and being stressed when things go wrong, I would also be.

I am glad to see you dive solo/tek/wreck, Please keep it that way :sarcasm: You have all the knowledge and skill combined with some thoughtful planning to execute these activities safely.

 

[Instructor_Tom]

tskovan;

first let me say that I am certified to both side mount and back mount and i really like the maneuverability i get with side-mount but I am in the process of undergoing intense overhead environment training and would not even think of diving side-mount at this time..

I know in you post you said that overhead environments are of no interest to you, but that is where manifolded doubles becomes a requirement. Under IANTD manifolded doubles are required for overhead environment training if not training in a CCR.

the reason for manifolded doubles is easy, gas management simplicity. with manifolded doubles I have 2 shut off valves 1 for each of my second stages and a shut off valve on the crossover in the event that I loose an O ring on one of the tanks ( highly unlikely on a 300bar valve). the cross over is always left open period unless you loose an O ring, so fills are a none issue.

the big difference between side mount doubles and manifolded doubles is gas management. on the side mount configuration I have to gas match my tanks within 500PSI of each other to account for a complete failure of one of my tanks so that I can safely make it out of a cave. At depth dealing with narcosis and the heavy task loading ( running a reel or navigation) this becomes more difficult to remember to do and it is possible to find your self over 1000PSI off on your tank balance. A tank failure can then quickly become a serious issue and you might have become a statistic.

I know many people are switching to side mount in over head environments because its easier to get in and out of the water,but until they can handle a high level of task loading I think they are asking for complications on their dive.


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