double tank equipment

[cool_hardware52]

My understanding is that when one breathes from a regulator on a set of doubles with the isolator open, the gas delivered is drawn initially and primarily from the tank to which the reg is attached. There is a slight lapse (perhaps a second or two) between inhalation and the pressure being equalized as gas transits across the manifold to re-establish equilibrium. I do not believe there is any "mixing in the first stage."

Certainly would be interested to read the results of any experiment!

Nope. Just look at the internals of a manifold. The cross bar is about .08-.100" diameter. For the phenomena you describe you'd need a *tiny* hole, like the one in the reg end of a HP hose.

If what you suggest is true, the reverse, i.e. filling unequally, would also have to be true, and fill rates are often orders of magnitude greater than the rate at which a diver consumes gas.

If I'm filling ~200 cuft in 10 minutes that 20cf/min and using it at .5 cu ft / min the fill rate is 40 X the consumption. Any restrictions in the manifold would far more evident during filling.

If one introduces a single fill gas (O2, He, Air) via a single post do they not fill each tank equally? If not one would expect analysis of PP blended doubles to routinely differ from post to post. They don't if the manifold is cleared of the last gas introduced (short blast)

Try this: PP blend some EAN32 to 3000 PSI. Start with empty doubles. Slowly introduce 420 PSI of O2 via a single post. Slow, (good idea with O2 anyway), now we have absolutely the same amount of O2 in each tank.

Now blast in the ~2580 Psi of Air. Crank it. Clear each post (short blast out) and analyze.

If the manifold represents a restriction one would expect the Air to enter the tank "under' the post the whip was fitted to, mix a bit with the O2 there and then some of this "enriched air" would migrate over to the second tank. That would result in the "other" tank having a higher O2 % than the first. Doesn't happen.

Why? Gas moves from areas of high pressure to low pressure and even at the flow rates represented by rapid filling the manifold presents no significant restriction compared to the tank "under" the post the fill whip is attached to.


BTW I researched this very question when designing manifold extensions for some RB's with manifolded dil bottles.



Tobin

 

[AfterDark]

My understanding is that when one breathes from a regulator on a set of doubles with the isolator open, the gas delivered is drawn initially and primarily from the tank to which the reg is attached. There is a slight lapse (perhaps a second or two) between inhalation and the pressure being equalized as gas transits across the manifold to re-establish equilibrium. I do not believe there is any "mixing in the first stage."

Certainly would be interested to read the results of any experiment!

Thanks I mentioned that in one of my posts, that the post the reg is on may have some bearing on how much of each gas would be delivered. You didn't see it because it was many posts ago and those that have been quoting me have been taking what I posted cutting it up and presenting what they want to, which often put what was posted out of context. A little game I've been watching in this thread for about a week. I thought it was an interesting hypothetical question.

---------- Post added June 25th, 2015 at 11:49 AM ----------

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. Since the mixing would take place in the regulator which regulator the diver is using may also affect the mixing of the gases. There are a lot of variables involved.

There it is: which regulator the diver is using may also affect the mixing of the gases. Of course that equities to which post the reg is on.

 

[Doppler]

Nope. Just look at the internals of a manifold. The cross bar is about .08-.100" diameter. For the phenomena you describe you'd need a *tiny* hole, like the one in the reg end of a HP hose.

.... stuff snipped...


BTW I researched this very question when designing manifold extensions for some RB's with manifolded dil bottles.



Tobin

Thanks Tobin... any data to confirm or bust the "mixing in the first stage" issue?

 

[cool_hardware52]

Thanks Tobin... any data to confirm or bust the "mixing in the first stage" issue?

If each tank supplies equal amounts of gas to a single orifice I would expect them to "mix" where they first meet, and that would be at the juncture of the manifold and a single post.

Not sure how anybody thinks the gas from one tank, and the gas from the other can share passage from the dip tube / manifold juncture to the post valve and on to the orifice without mixing.........

Fairly small passage, quite convoluted, fairly long diameter to length ratio. Magical forces would be required to keep these gas "streams" apart until they reach the first stage.

Tobin

 

[decompression]

This image always helps when getting your head around how a manifold functions....




Sent from my iPhone using Tapatalk

 

[Adobo]

The original question spawned 235 replies worth of discussion. A lot of good information, to be sure. Quite a bit of it has been focused on manifolds - how to operate them, what position valves should be in when filling, when diving, more detailed discussions on the inner workings, etc.

I got curious about whether the original poster got anything out of this thread; I found it odd that we really haven't seen him reply back since the original post. It turns out that he has a few posts recently related to sidemount - a way to dive two (or more) tanks during a dive that does not involve manifolds. So I guess for all the discussions we have had on the perils of diving double tanks, most of the discussion was probably not of particular interest to the original poster.

Go figure.

 

[Divin'Papaw]

The original question spawned 235 replies worth of discussion. A lot of good information, to be sure. Quite a bit of it has been focused on manifolds - how to operate them, what position valves should be in when filling, when diving, more detailed discussions on the inner workings, etc.

I got curious about whether the original poster got anything out of this thread; I found it odd that we really haven't seen him reply back since the original post. It turns out that he has a few posts recently related to sidemount - a way to dive two (or more) tanks during a dive that does not involve manifolds. So I guess for all the discussions we have had on the perils of diving double tanks, most of the discussion was probably not of particular interest to the original poster.

Go figure.

... or we scared him into sidemount!!

Although that method, as with all, has it's own challenges. All configurations are just tools and each has strengths and weaknesses.

 

[nimoh]

The original question spawned 235 replies worth of discussion. A lot of good information, to be sure. Quite a bit of it has been focused on manifolds - how to operate them, what position valves should be in when filling, when diving, more detailed discussions on the inner workings, etc.

I got curious about whether the original poster got anything out of this thread; I found it odd that we really haven't seen him reply back since the original post. It turns out that he has a few posts recently related to sidemount - a way to dive two (or more) tanks during a dive that does not involve manifolds. So I guess for all the discussions we have had on the perils of diving double tanks, most of the discussion was probably not of particular interest to the original poster.

Go figure.

Because of your post, I went and took a look at the original post, and it doesn't actually specify backmounted manifolded doubles...it may well have been about sidemouted doubles, possibly even a UTD Z

so my answer to the OP after 236 posts is....it depends

 

[cool_hardware52]

Because of your post, I went and took a look at the original post, and it doesn't actually specify backmounted manifolded doubles...it may well have been about sidemouted doubles, possibly even a UTD Z

so my answer to the OP after 236 posts is....it depends

Which is exactly what I told him......


Tobin

 

[Adobo]

Which is exactly what I told him......
Tobin

On the very first reply to the question.