Double Tank Manifolds, Bad Idea!

[MaxBottomtime]

From the OP: I think it’s all been said, to sum it up

MD: a) A slight reduction in redundancy
b) Simpler gas management
c) The possibility of retaining more gas after a failure
d) More complexity under stress (managing a failure)
e) Twice the weight and bulk when filling, moving, storing, loading on or off a boat ect.

ID: a) Total redundancy
b) Higher task loading for gas management (not under stress)
c) Loss of half your gas after a failure
d) Less complexity under stress (managing a failure)
e) The simplicity of managing cylinders as singles, once removed from the bands

I choose IDs, you choose what you like, Thanks to all those who responded intelligently.

MD: a) More redundancy than ID. I can close the valve in the event of a regulator leak or failure and still have access to all my gas.
b) As simple as diving a single tank
c) The possibility of retaining all of your gas after a failure.
d) With a little practice, valve manipulations becomes easy with muscle memory.
e) Twice the weight, but all of the above can be done in one move rather than two.

ID: a) No redundancy. If you have to close a valve you are down to whatever you have remaining in the other tank.
b) True
c) True
d) More complexity under stress. After closing a valve you now have to manage your ascent with a lot less gas than you planned.
e) Easy to manage as singles, but tiresome having to remove bands after every dive.

 

[AfterDark]

How is gas sharing managed in ID's?

I use my ID's for solo diving, no gas sharing methods needed. I have slung a pony for OOG handoffs when using my IDs on rare occasions diving with a buddy.

---------- Post added September 23rd, 2013 at 07:01 PM ----------

MD: a) More redundancy than ID. I can close the valve in the event of a regulator leak or failure and still have access to all my gas.
b) As simple as diving a single tank
c) The possibility of retaining all of your gas after a failure.
d) With a little practice, valve manipulations becomes easy with muscle memory.
e) Twice the weight, but all of the above can be done in one move rather than two.

ID: a) No redundancy. If you have to close a valve you are down to whatever you have remaining in the other tank.
b) True
c) True
d) More complexity under stress. After closing a valve you now have to manage your ascent with a lot less gas than you planned.
e) Easy to manage as singles, but tiresome having to remove bands after every dive.

Why close a valve on ID's? Makes no difference after a failure, the gas is of no use, part of the simplicity. One of the reasons I use ID's is because I can't reach valves behind me.

I open them at the start and close them at the end just like single tanks because that's what they are.

The underlined bold statement is not necessarily true. If a diver is planning to turn at lets say 1500PSI and a failure happens mid dive the gas left in one tank is more than enough. If the failure happens towards the end of the dive that statement might be true.

 

[tskovan]

MD: a) More redundancy than ID. I can close the valve in the event of a regulator leak or failure and still have access to all my gas.
b) As simple as diving a single tank
c) The possibility of retaining all of your gas after a failure.
d) With a little practice, valve manipulations becomes easy with muscle memory.
e) Twice the weight, but all of the above can be done in one move rather than two.

ID: a) No redundancy. If you have to close a valve you are down to whatever you have remaining in the other tank.
b) True
c) True
d) More complexity under stress. After closing a valve you now have to manage your ascent with a lot less gas than you planned.
e) Easy to manage as singles, but tiresome having to remove bands after every dive.

So, what you’re saying is that your way is superior in all aspects and my way is inferior in all aspects, OK. I would define that as fanatical devotion. I learned a long time ago not to try to argue logic and reason with a fanatic. Thank you for your reply, I will give it all the consideration I think it deserves.

 

[MaxBottomtime]

No, I was saying that a manifold gives more redundancy because you don't automatically lose half of your gas when you close a valve. If that makes you believe that anyone with a differing opinion is a fanatic, then perhaps you should find another outlet for your writings than the internet. I believe that you haven't thought the idea of doubles configurations through before deciding to tell everyone that manifolds don't make sense. Others have tried to explain it to you, but your mind was made up before you even started this thread.

 

[DaleC]

I'll take a stab at both Q's.

For me, air share is exactly the same as a Hog manifolded diver. The clip on my long hose reg is held on with bicycle tubing so it can tear away if clipped off. So.. If I'm on the long hose I donate that. If I'm on the bungied B/U I either unclip the long hose and donate or just pull it free from the clip. Statistically speaking, I am more likely to need to donate in the second half of the dive (OOA) so I breath the Bungii first and then go on the long hose for that portion of the dive.

I only do one reg swap during the dive (usually). I determine my Rock Bottom reserve level and breath the first cylinder down to that, switch and breath the second down to that, then begin ascent. At any point I have enough gas to ascend on either cylinder so there is no stress in ascending with less gas than I planned for. If I am multi-level diving I may adjust to a new shallower RB and breath each tank down to that etc...

This access to all gas concept is interesting but I look at it differently as a solo diver. If diving RB it should make no difference. If diving thirds you have 1/3 in, 1/3 out, 1/3 reserve. So at the worst possible moment I could lose one cylinder and still have 1/6 out, 1/6 reserve... but for a solo diver. The MD diver would have 1/3 out, 1/3 reserve, but for a team (which is 1/6th each). One could argue that 2/3's is better than 1/3 but then 500cuft would be better than 140cuft (so the argument goes).

 

[tskovan]

No, I was saying that a manifold gives more redundancy because you don't automatically lose half of your gas when you close a valve. If that makes you believe that anyone with a differing opinion is a fanatic, then perhaps you should find another outlet for your writings than the internet. I believe that you haven't thought the idea of doubles configurations through before deciding to tell everyone that manifolds don't make sense. Others have tried to explain it to you, but your mind was made up before you even started this thread.

I called you a fanatic because you rewrote my pro’s and con’s list so that your system has nothing but pro’s and my system has nothing but con’s, which is ridicules. To believe that everything you do is correct and everything someone else does is wrong is the definition of a fanatic. But maybe I misconstrued the spirit of your post and your just arguing your side, if so I apologize for the name calling. I have said from my OP that both systems have pros and cons, But that I don’t use manifolds, and listed the reasons why.

But you actually state in your post that: MDs are more redundant, and that “ID’s have no redundancy” That is an utterly inaccurate statement. The ability to perhaps save some or most of the gas in a malfunctioning tank is what actually reduces the redundancy of the system, by connecting the tanks together there is also the possibility of loosing all the gas in both tanks in certain situations (see previous posts for examples).
I have been involved in aircraft systems design for many years and have a deep understanding of what true redundancy is and is not. To say that “ID’s have no redundancy” and then accuse me of “having not thought the idea of doubles configurations through” is a bit absurd.

Perhaps you should rethink the possibility there’s more than one way to accomplish the same task (and could possibly even be better!). My mind is not made up on this issue, and I have moderated some of my opinions based on replies I’ve gotten here, but IMO the twisted logic of your arguments are incredibly unpersuasive.

 

[AfterDark]

Part of the "disagreement" comes from the perceived use of ID v MD. My perspective has always been that ID's are used for OW solo diving not overhead environments. Just look at the concerns and questions.....air share with IDs, closing valves on ID's. Solo diving doesn't offer much opportunity to share air and as posted earlier closing valves on IDs is not necessary. MD's are better for overhead environments because all remaining air is available, without access to the surface this could be critical. Just like any other piece of gear ID's and MD's have their place, one is better for some diving than the other. For older guys like me that don't feel up to dragging MDs around but want the gas capacity of double tanks IDs are a good compromise.

Also cost has not been mentioned yet. I have 3 sets of tanks I use for ID’s any of those tanks can be used for single tank buddy diving at any time. I bought them all used so I spent even less. What would 3 sets of MD’s and 6 single tanks cost? BIG BUCKS! I have 6 different configurations of tanks I can dive that cost me less than $500.00. In my world of diving IDs have it all over MD’s, maybe not for you.

Why is it that I never see the sidemount config. criticized for not being able to access all the divers air after a reg malfunctions, only the ID's? Is there some magic I'm not aware of that allows a diver access to all remaining air in the sidemount config after reg failure?

Could it be that SM is the latest and the greatest and new gear to sell? And wasn't side mount started for cave diving? Seems a little odd to me since a diver can't access all remaining gas after a reg malfunction with side mount.

---------- Post added September 24th, 2013 at 08:51 AM ----------

All this reading and posting has made me decide to go diving! This is my last week out of work due to surgery 10 weeks ago, I'm going to enjoy it! Just packed my car and I'm off to Newport for 2 air fills then one solo dive with my 50cuft ID's. I'll post when I get back.

 

[flots am]

Why is it that I never see the sidemount config. criticized for not being able to access all the divers air after a reg malfunctions, only the ID's? Is there some magic I'm not aware of that allows a diver access to all remaining air in the sidemount config after reg failure?

If you really wanted to and had a 3rd tank to breathe off for a minute or two, you could swap regs underwater, although it would require service later.

 

[TSandM]

The advantage of sidemount is that, if your problem lies in the regulator, you can feather a valve and still have access to the gas in that tank, which is not really very feasible if the valve is on your back. Obviously, a tank neck o-ring or valve problem can lose you all the gas in one tank, but that's true with sidemount, IDs, or MDs.

The big reason for having the tanks on your back is that they are connected to one another, and it's hard to do that any other way. If you aren't going to connect them, having them where you can't reach the valves easily just seems like an odd choice.

 

[DaleC]

I believe a SM diver could feather the valve if they needed to but so could a BM diver if they loosened the harness (but as stated previously, not needed for our applications).
One can also dial back a freeflowing tank and extend its breathable duration in a pinch. I've been working on a Le Prieur set up that demonstrates this.

[video=youtube;Y7STLNzjHnk]http://www.youtube.com/watch?v=Y7STLNzjHnk&feature=c4-overview&list=UU5zvhnU0XYpf_cadpYJYkhQ[/video]

Lynne, you posted while I did

The access issue has two rebuttals of varying strength, depending on ones needs/wants.

The first is that for some diving, access is not needed. One can reach back and shutdown if one wants which is all one would really need to do if gas planning correctly. Continuous access is a want, not a need.

Switching to SM has some costs that a diver may not want to assume to do something they already can do (training/equipment).