First set of doubles looking for advice

[Waterskier1]

The only downsides to independant tanks are:

2) If you do have to shut down a tank then you have just lost access to maybe half you gas.With manifolded doubles you would still have access to all of it. Again not a big problem on NDL or limited limited deco dives.

I am assuming you mean shutting down the reg on that manifold post. If you shut down the tank, by the tank valve, you would not have access to the contents of that tank. And, if it were a free flow, you probably would not have cured that problem either (by shutting the tank valve, versus the manifold post). Is this correct? Can you shut down (isolate) a tank on the manifold? Or, you only isolate the regs on each side from one another? Or both? I'm don't have any experience with doubles or twins - yet.

In any case this is a good point and one that I didn't think of. I don't think it will be a major problem for my Recreational Diving though. It will just be something I will need to take account of during my dive planning. If I do get into Tek Diving, I'll end up get a full manifold setup, and probably the tanks won't be AL80s.

 

[ianr33]

I am assuming you mean shutting down the reg on that manifold post. If you shut down the tank, by the tank valve, you would not have access to the contents of that tank.

That is not correct.

With manifolded doubles if you shut down the right "post" for example you still have access to ALL the gas in both tanks via the reg on the left post.

The manifold is below the valve.

It makes more sense when you dive them!!

Edit: Being able to isolate a malfunctioning reg and still have access to all your gas is one of the great advantages of manifolded doubles. Burst a low pressure hose: Turn the reg off and call the dive. No big problem although I am sure there would be some excitement for a few moments!

If the problem is below the manifold (Burst disc or tank neck O ring) then the only solution is to close the isolator valve. You will lose all gas in the affected tank but the other tank will be O.K. If the leak is bad then you need to close the isolator QUICKLY!

The only way you can lose all gas is to either not react quickly enough to a problem or to break both sides of the isolator which is incredibly unlikely.

 

[Waterskier1]

Isn't that what I said? I think the only difference is that there *may* (I am not sure) not even be a tank valve when you use manifolds. That is, the manifolds screw directly into the tanks, such that there is no way to shut off the tank. Certainly, you can shut down the reg, and even isolate the the two.

Have I stated it correctly, or do I have a fundemental misunderstanding of manifoled doubles?

 

[ianr33]

Sorry if I am not being clear. Try looking at it this way:

The manifold joins the tanks together. It will always have tank pressure in it. If you have a problem that causes loss of gas from the tank (as opposed to the reg) then you have to close the isolator.
Problem with a reg then close the "post" (same as "valve" on a single tank)

 

[Waterskier1]

Got it, Thanks!

 

[micklock]

When you go to Bonaire you should see if they have AL 63's that would be a cool twin setup.