O2 Injection Point

silent running

Hi Steve, I think this is the big, overiding reason to have O2 add on exhale
side, especially with He mixes as O2 and He don't mix easily and need time/room to mingle... -Andy

bubnotbub

Hi,
but when the solenoid fire on Inspiration,
where arrive quickly the O2?

Regards

Aldo

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ScubaDadMiami

A feature of the Optima, besides having the O2 manual inflate on the exhalation side, is that it injects O2 from the solenoid just prior to the scrubber cartridge (through the cartridge core via a hollow delivery tube that runs from the solenoid to the injection point), allowing gas in the canister plus the inhalation counterlung to mix prior to reaching the DSV. Also, this mixing facilitates less spiking, and hence a more stable and accurate read when the gas reaches the O2 sensors due to the mixing inside of the canister.

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silent running

Just thought of another reason why having O2 on exhale might be better, it makes cal. easy, at least on the Prism. Our cal. procedure-after checking O2 supply purity-is to suck the loop down to negative, crack open the DSV slightly, then flow O2 manually from exhale lung, watch the needle rise to 1.0, stabilize, close DSV, wait-if no change press cal button wait for flashing green fron HUD-go. I don't see how this would be possible on a unit with O2 add on the inhale-it would flow out the DSV if it were cracked. If the DSV were left closed, it would over pressure and give a false 1.0. Am I missing something? -Andy

divetheworld

What gives you this idea Andy?

Here comes the science bit.....
Diffusion of low density gases is much faster than that of high density gases. The rate of diffusion of a gas is inversely proportional to the square root of the molecular density of that gas.
in the case of He and O2/N2 the masses of those gases are vastly different so the inherrant kinetic energy on the molecules is also vastly different as a constant temperature. Since the average kinetic energy of different types of molecules (different masses) which are at thermal equilibrium is the same, then their average velocities are different. Their average diffusion rate is expected to depend upon that average velocity, which gives a relative diffusion rate. Therefore using Grahams law, the rate of diffusion of He into O2/N2 (or O2 into He/N2) is faster than the diffusion of O2 into N2.

Brent.

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Silent

Blimey Brent, that was a great explanation of that especially considering the time of morning when you posted it!

You start on the super strength espresso early this morning??

I'd give you green for that but have to spread some around first

Neil

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hirudin

-Quote from Steve-

"...I have been running my Meg with the manual O2 addition on the exhalation lung for some time now ..."

Steve,

Do you simply route the manual O2 addition into the mixed gas bypass, or do you actually switch the inhale/exhale CL's?

-Jesse-

silent running

Hello Brent, thanks for the sceince explanation. I had heard this He not mixing with O2 thing in regaurd to how these gasses mix in the loop from 2 different people, maybe I misunderstood the idea. I can see that the differing gas densities would allow for a faster diffusion rate. But how fast is fast? Would it be near to instantaneous? There is not much time in btw the respritory cycle that pushes the gas around the loop, so this is why I ask. Thanks, -Andy

Yann A.

Since the average kinetic energy of different types of molecules (different masses) which are at thermal equilibrium is the same, then their average velocities are different. Their average diffusion rate is expected to depend upon that average velocity, which gives a relative diffusion rate. Therefore using Grahams law, the rate of diffusion of He into O2/N2 (or O2 into He/N2) is faster than the diffusion of O2 into N2.

Brent.
[/quote]

Thanks Brent for your explanation,

I had asked the question on another forum some months back but without any reply. Now I get the begining of one. How fast is O2 going to mix in the inhale lung? As from what I remember from my chemistry classes it should be quasi instant... Now at depth it could be different due to different gas density, maybe.
I dive a Meg and would be interested to see some numbers. English isn’t my mother tongue so something like: I press my manual O2 injector for “x” seconds, I get that much O2 in my CL if I inhale at the same time I breathe “y%” of O2.
I’m just thinking out loud here but to me numbers talk more than words sometimes.
It used to be a time where people used to tumble their nitrox tanks after blending….

Yann.

JonnyB

Thanks Brent for your explanation,

I had asked the question on another forum some months back but without any reply. Now I get the begining of one. How fast is O2 going to mix in the inhale lung? As from what I remember from my chemistry classes it should be quasi instant... Now at depth it could be different due to different gas density, maybe.
I dive a Meg and would be interested to see some numbers. English isn’t my mother tongue so something like: I press my manual O2 injector for “x” seconds, I get that much O2 in my CL if I inhale at the same time I breathe “y%” of O2.
I’m just thinking out loud here but to me numbers talk more than words sometimes.
It used to be a time where people used to tumble their nitrox tanks after blending….

Yann.[/quote]

Hi Yann, first of all you will not press the manual addition for X number of seconds, then you should try to synchronize it with an exhale, this way you will push the new O2 added around the whole loop, so you will get it mixed for a longer period of time.

/Jonny

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