double tank equipment

[Jack Hammer]

It's absolutely becoming clear to me. Unfortunately, the Doubles course I mentioned I planned to take is now on hold, as my plan was to do a combined Doubles and Drysuit course, and I just learned my drysuit delivery has been delayed. What kind of education is needed to learn to use a drysuit has been the subject of similar debate.

Both can be learned from competent mentoring. Not everyone has access to this and some opt for a class

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[cool_hardware52]

Both can be learned from competent mentoring. Not everyone has access to this and some opt for a class

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Who here has claimed otherwise?

Tobin

 

[AfterDark]

This is a great discussion. My comments are from real world experience. I don't dive trimix nor do I home blend nitrox, but I have experience transfilling different Nitrox blends between my own tanks. I have transfilled a set of doubles from another tank with a higher O2 mix, and waited to see how long it takes for both sides of the doubles to reach the same O2 percentage. It never happens! Not within a time frame that is practical in the real world! I've waited hours as well as days and then a few weeks and then retested both sides. The two sides don't mix (and yes, the manifold was open!). Now I supposed if I let them sit for 6 months they might, but that's just not a real world application of how we use scuba gear.

---------- Post added June 24th, 2015 at 09:29 AM ----------



I think this is a critical point. When it comes to doubles connected via a manifold (vs. gas in one large tank), we need to appreciate that the gas in the two tanks acts more like a liquid than a gas.

Hopefully it's now becoming very clear that diving doubles is more complex than treating it as just one large tank! There are new skills, new techniques and new concepts to be learned and applied.

Did you put a regulator on it try to analyze what comes out of the 2nd stage? That's where any mixing would take place.

 

[Divin'Papaw]

Both can be learned from competent mentoring. Not everyone has access to this and some opt for a class

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I believe I specifically mentioned this as a viable option, so yes, I agree completely.

 

[cool_hardware52]

Did you put a regulator on it try to analyze what comes out of the 2nd stage? That's where any mixing would take place.

Why are we even considering "mixing" in the manifold? It's foolhardy to consider ever using doubles with differing mixes in each tank. What if you had to Isolate?

Haven't you already stated that you have never filled a tank? I have, too many to count. Most of them PP blends.

Filling and analyzing and ending up with the mix you want is part science and part art, or at least understanding the peculiarities of the fill station you are using. This is particularly true with Trimix.

The immediate reaction I'd have to any set of doubles that analyzed differently from post to post is "The blender may be incompetent"

That's enough for me to refuse to dive the gas. What other mistakes did this blender make?

An gas analyzer is like a SPG, it should only confirm what you expect to find. It the results are otherwise it's time to dump some gas, and have a personal chat with the blender.

Tobin

 

[nimoh]

Did you put a regulator on it try to analyze what comes out of the 2nd stage? That's where any mixing would take place.

Why do you think that mixing would take place in the second stage and not the hose going to the second stage, the first stage or the manifold with the manifold being the first place the gases come together when purging the second stage.

As this has shifted to a practical discussion vs a theoretical one, it really doesn't matter, as there is no practical reason to put a regulator on a set of doubles with different mixes in each tank. But I'll ask anyway.

 

[Divin'Papaw]

Did you put a regulator on it try to analyze what comes out of the 2nd stage? That's where any mixing would take place.

That's completely irrelevant. Open the valve ... test the gas that comes out. The regulator is irrelevant. It is simply going to delivery to the diver the gas that comes out of the tank, and that mix is what it is. The regulator isn't going to magically mix the gas for you!

 

[Lorenzoid]

Both can be learned from competent mentoring. Not everyone has access to this and some opt for a class.

Your post replies to mine, so I'll reply to yours: You are repeating the same thing that others have said several times in this thread. The point has been well made. Nothing in my comment contradicted that point. I have no horse in that race. My post mentioned what my own plans are for myself, that's all. Despite my efforts to phrase my post carefully, so that nobody would think I am trying to make a point, someone felt compelled to bring it up again. Sheesh.

 

[Adobo]

Did you put a regulator on it try to analyze what comes out of the 2nd stage? That's where any mixing would take place.

Unless the gas in each cylinder was nominally the same mix, it wouldn't make sense to assume that whatever the end product of that would be something you would want to breath or to dive.

For example, if you had 21%(air) in one cylinder and 32% in the other cylinder and your analysis came up to 26.5%, based on what mix would you determine your no deco limits? Would you trust that the gas you are breathing is always 26.5% or would you plan on depth limits based on 32%?

In my mind, if you are in this situation, it is basically a fuster cluck and the best thing to do is not be a nickel rocket, dump one of the cylinders and then get proper fills.

If the gas in one or both of the cylinders is trimix, then it means you are thinking about doing a more "substantial" dive. And if your cylinders don't have nominally the same mix in this scenario, you have a giant fuster cluck even before you get in the water. The best thing would still be, fix it before you go diving. (Dump the contents of one of the cylinders into a stage bottle, etc.)

 

[victorzamora]

Unless the gas in each cylinder was nominally the same mix, it wouldn't make sense to assume that whatever the end product of that would be something you would want to breath or to dive.

For example, if you had 21%(air) in one cylinder and 32% in the other cylinder and your analysis came up to 26.5%, based on what mix would you determine your no deco limits? Would you trust that the gas you are breathing is always 26.5% or would you plan on depth limits based on 32%?

In my mind, if you are in this situation, it is basically a fuster cluck and the best thing to do is not be a nickel rocket, dump one of the cylinders and then get proper fills.

If the gas in one or both of the cylinders is trimix, then it means you are thinking about doing a more "substantial" dive. And if your cylinders don't have nominally the same mix in this scenario, you have a giant fuster cluck even before you get in the water. The best thing would still be, fix it before you go diving. (Dump the contents of one of the cylinders into a stage bottle, etc.)

I saw someone fill their "tanks" with the isolator closed. They realized it a few hundred miles from home, at the dive op, and decided to leave it closed and get the other tank filled. Two different mixes. He treated them as Independent Doubles. This was a rec-only trip, so he dove one on one dive and then the other on the second dive. I thought it was pretty clever!