double tank equipment

[agilis]

With 2 "equally" filled tanks the mixing would go on in the regulator how much and the % of mix depends on which bottle has the higher pressure the higher pressure gas would have the >%. Higher on 2 equally filled tanks?

Both tanks may read the same on a gauge but since there are tolerances on the gauges, one tank may have a higher pressure small enough not to be read on the gauge but never the less exerts that much more pressure. I would also say the density of the gases involved would have some bearing on the % mixed also.

Yes, and so would its correlative, the temperature, specifically the speed of molecular motion. The 'small' passageway connecting both sides of the manifolds section is utterly huge in terms of molecular size and movement.

I think some people may have had a bit of confusion over the word 'mix' associating it with mixed gas diving or trimixes. Plain atmospheric air is a mixed gas, as are all levels of nitrox. In fact, atmospheric air is basically nitrox. Blended, mixed, just a lot of synonyms. Rote training may not make this clear. A deeper understanding will.

 

[Lorenzoid]

It's just not the reality of it. In sure if u have a bajillion years it would even out, but here in real life it doesn't. See tobins comment about the diameter and length of the manifold.

The gases behave more like liquids at scuba pressures.

Okay, thanks AJ. That jibes with my understanding of the physics of molecular gas diffusion (though I suspect it would take somewhat less than a "bajillion" years). I have no real-world knowledge or experience with gases diffusing through tiny orifices.

 

[cool_hardware52]

If you took a set of doubles with the isolation manifold closed, and filled one tank with 100% O2, and the other with 100% He. Both tanks to the exact same pressure and temperature....
Unless you have an orifice that is only the diameter of 1 atom, when you open the isolation manifold the 2 tanks will eventually become thoroughly mixed. How long will that take? I don't know, you'll need to break out the slide rule. I believe these are the ideal gas laws dealing with diffusion and Effusion. The gas particles are constantly in motion, and all the O2 molecules are trying to get as far away from each other as possible; same with the He molecules.

Consider the size of the "mixing front" ~.100 or less and the length of the conduit, the effective length of this .100" diameter "tube" internal in the manifold is ~5 inches from one cylinder to the center of the manifold. That's a length to diameter ratio of 50:1

Long thin tube.

For a single molecule of O2 to pass from the tank of O2 and into the Tank of He would require it pass through this long thin conduit.

Some will of course eventually diffuse into the opposite tank but as a practical matter, confirmed by real world testing, the time required is geologic in nature. Real world tests using O2 and Air have been conducted by divers I consider to be quite well qualified. The results were essentially no change in analysis after *months* of sitting with an Open Isolator. That's good enough for me.

BTW how many angels can dance on the head of a pin?

Tobin

 

[agilis]

*sitting* is the issue.

St Thomas Aquinas resolved the angel question nearly a thousand years ago when he postulated the impossibility of any effect having more than one immediate cause. In modern physics the Pauli principle approaches the question from another perspective by establishing the impossibility of more than one thing occupying the same space at the same time.

There is also a distinction to be made between dancing angels and sitting angels, similar to the difference between a compressed air breathing apparatus sitting motionless in one place and that same apparatus in use, having air withdrawn from it by a diver.

 

[cool_hardware52]

What's my protocol if doubles get filled with Iso Closed?

Analyze both sides.

Pick one to save, usually the one with the most Cuft of He

Dump the other side, or jack it into a stage bottle if the mix looks like it's worth saving.

Open the Isolator.

Re analyze and fix the mix.

Blending is tricky enough without invoking incantations over a screwed up set of doubles or waiting for Brownian Motion to eventually save the day.


Tobin

 

[CptTightPants21]

What's my protocol if doubles get filled with Iso Closed?

Analyze both sides.

Pick one to save, usually the one with the most Cuft of He

Dump the other side, or jack it into a stage bottle if the mix looks like it's worth saving.

Open the Isolator.

Re analyze and fix the mix.

Blending is tricky enough without invoking incantations over a screwed up set of doubles or waiting for Brownian Motion to eventually save the day.


Tobin

I guess it would depend on the exact mixes (trimix vs Nitrox), but how much of the one side would you need to dumb/transfer for it to be safe/usable? Would draining one side to 500 psi and then opening the iso valve allow for enough mixing?

 

[KevinNM]

In theory you could jump into the water, go to 15 meters and happily breath 50/50. I'd advise against trying it, as what I think would actually happen is death due to either oxygen toxicity or hypoxia.

 

[cool_hardware52]

I guess it would depend on the exact mixes (trimix vs Nitrox), but how much of the one side would you need to dumb/transfer for it to be safe/usable? Would draining one side to 500 psi and then opening the iso valve allow for enough mixing?

100% of one side. That way when you open the Iso you know that you have what ever mix you kept in the other tank distributed equally on both sides.

Trying to "tune up" a set of doubles by adding differing amounts of various gas to each side is problematic, particularly with He mixes. Hard to do, hard to get an accurate analysis, just not a good idea.

Adding small amounts of He as the final gas is really tricky, it just doesn't mix well.

Dumping one side is also far faster. It allows the embarrassed blender who failed to check that the ISO was open to more quickly hide his sins.....

Tobin

---------- Post added June 23rd, 2015 at 05:11 PM ----------

In theory you could jump into the water, go to 15 meters and happily breath 50/50. I'd advise against trying it, as what I think would actually happen is death due to either oxygen toxicity or hypoxia.

Your theory gets really grim if you actually need to Isolate......

Tobin

 

[Divin'Papaw]

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 ----------

It's just not the reality of it. In sure if u have a bajillion years it would even out, but here in real life it doesn't. See tobins comment about the diameter and length of the manifold.

The gases behave more like liquids at scuba pressures.

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.

 

[Lorenzoid]

. . .
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.

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.