Manifold open or closed?

[Diver0001]

I can also recover un-lost gas using the manifold if and when the situation warrants it.

I can't follow this part. If you ahve some kind of major malfunction that caused you to lose all gas on one post then how is opening the manifold after the fact going to help anything?

I can kind of 1/2 follow your logic. If you assume that for some reason you were totally unable to reach your valves then being *unable* to shut down would be a good reason to keep the manifold closed. Where you lose me is why you wouldn't just use independent twins then.....

R..

 

[VinceDS]

I'll second the - I dive with my manifold open ALL the time. If you are going to dive independants then by all means dive them. If you keep your iso. closed, you are asking for trouble. Plus, this defeats the purpsoe of a manifold..

 

[Diver0001]

I'll second the - I dive with my manifold open ALL the time. If you are going to dive independants then by all means dive them. If you keep your iso. closed, you are asking for trouble. Plus, this defeats the purpsoe of a manifold..

Why would it be asking for trouble? It doesn't have any function if it's closed but it's not like divers with manifolds are having major problems with them.

R..

 

[MikeFerrara]

The most common failures are those that require the closing of a single post...like a free flow. The benefit of manifolded doubles is that all the gas is in a single volume yet the ability to isolate exists. Meaning that we had redundant regs (the most likely failure point) providing access to the same volume. The downside is that if somehow a manifold failed in the wrong place you could suffer a total gas loss. Independants solve that problem but you have to deal with 2 seperate volumes.

Diving with a closed isolator gives you all the disadvantages of both systems with NONE of the advantages of either. Don't be afraid. With a little practice you can learn to shut down a valve in just a few seconds.

If you do lots of solo diving you might want to consider independants. In this case, don't be silly, sidemount them. Then you can remove them one at a time, see the whole valve and reg and fit through lower places.

 

[Diver0001]

....snip....

that if somehow a manifold failed in the wrong place you could suffer a total gas loss. Independants solve that problem but you have to deal with 2 seperate volumes.

I know what you're saying but how many catastrophic manifold failures have you seen or heard of in the last 5 years? I can recall one and it happened when the guy picked his kit up by the manifold (his tanks did a nice space shuttle imitation and he got a broken arm from what I heard)

I don't disagree with you--quite the contrary--but I just think people should keep the risks in perspective. That's what was behind my question to Vince. I figure if closing your manifold is "asking for trouble" then we should be losing collective bladder control whenever we cross the street....

R..

 

[wedivebc]

Let me make this as clear as I am able to. I could and do often dive independants. Since my steel tanks came with a manifold I use it as well. With the manifold shut I don't feel it is any riskier than independants (Ok maybe a failure point but not a biggie)
Let's say I have a failure while in a wreck where I am not able to immediately reach my valves I can switch regs, get myself in a more favourable position then shut down the offending post. If after doing that I decide I can benefit from the remaining gas in the affected side I can open the isolation valve, otherwise I can leave it alone and turn the dive. With proper gas managment I will have enough gas to complete a safe exit without the gas remaining in that tank but since there are 2 spgs I know how much and have that option.

 

[SeanQ]

Yeah...1700 psi of an unknown O2 % at that, unless we are talking about strictly air diving here

How does the F02 change when this happens? Let's say your diving doubles with EAN 32. The manifold is closed and you breath down half of one cylinder. When you open the manifold, will it not still be EAN 32? Perhaps I am missing something.

 

[Hyper-limits]

How does the F02 change when this happens? Let's say your diving doubles with EAN 32. The manifold is closed and you breath down half of one cylinder. When you open the manifold, will it not still be EAN 32? Perhaps I am missing something.

When you get your double fill you have to make sure the manifold is open. Then just before you go in the water you close it. So it wouldn't change anything if you had to open the manifold during the dive.

 

[VinceDS]

Why would it be asking for trouble? It doesn't have any function if it's closed but it's not like divers with manifolds are having major problems with them.

R..

Asking for trouble more from the standpoint that you are increasing task load. W/ iso. closed, you are essentially diving independent cylinders. If something does go wrong and you forget the valve is closed you could have a problem. In an emergency, people do forget things. That's why pilots use checklists. We don't have the luxury of checklists. If something goes wrong, it needs to be corrected quickly. For instance, w/ practice, valve shutdown is a quick procedure. Just my opinion...

 

[Jason B]

How does the F02 change when this happens? Let's say your diving doubles with EAN 32. The manifold is closed and you breath down half of one cylinder. When you open the manifold, will it not still be EAN 32? Perhaps I am missing something.

Suppose you had EAN36 in both tanks, closed the isolator and went diving. After the dive you get your tanks refilled and a shop that banks EAN30 (typical for the NC coast). They don't realize that the isolator is closed and fill one cylinder only. You analyze the tank and see you have EAN30 which gives you a MOD of 121 ft. You plan your dive to 115ft. No problem...until you switch to the other tank with EAN36 in it (with a MOD of 95ft @ 1.4/ 113ft @1.6).

Jason