A (stupid) gas blending question

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taimen

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I am wondering how gas mixtures behave in cascades or during transfilling.

If I connect two cylinders containing different mixes with a short 3ft decanting hose, how long it will take before gas mixtures equilibriate?
Or if doubles are filled with different mixtures and manifold opened?
 

rhwestfall

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you need a pressure differential to move/mix the gasses....
 

boulderjohn

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I am wondering how gas mixtures behave in cascades or during transfilling.

If I connect two cylinders containing different mixes with a short 3ft decanting hose, how long it will take before gas mixtures equilibriate?
Or if doubles are filled with different mixtures and manifold opened?
Ages.

I tried it a couple of years ago with two tanks of different mixes. I wanted them to end up with about the same mix, so I connected them with a fill whip in the afternoon. I came back the next day and found both tanks had exactly the same mixes as they had the day before.

We had a thread on this topic on ScubaBoard about a year or so ago, and many people related the same experience.
 

Wookie

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Depends on how fast you put the second gas in. I find that the slower you add the second gas, the longer it takes to get a uniform blend, and in the case of a set of doubles, lets say you have 32% in one side at 3,000 PSI and 21/35 in the other side at 3,000 PSI, it would probably take months to get them to equalize mixtures.
 

boulderjohn

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So I guess we are not sure what you are talking about. Are you asking about adding new gas to a tank that is only partially full, or are you trying to get two separate and full tanks to mix through a connection?
 

taimen

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So I guess we are not sure what you are talking about. Are you asking about adding new gas to a tank that is only partially full, or are you trying to get two separate and full tanks to mix through a connection?

I was asking about mixing separate tanks with different mixes through a connection. Exactly the situation you @boulderjohn and @Wookie answered.
 

rhwestfall

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without a pretty good pressure differential, then "forever"...
 

taimen

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you need a pressure differential to move/mix the gasses....

Well there is partial pressure differential if the mixes are different. It seems that diffusion through a fill whip is just too slow to be practical.
 

Wookie

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Well there is partial pressure differential if the mixes are different. It seems that diffusion through a fill whip is just too slow to be practical.
This^^^^
 
https://www.shearwater.com/products/swift/

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