Set Point ( Confused )

big bootie bottom

I Dive A Homebuilt Scr And I'am About To Finish My First Mccr As Soon As I Get The 02 Meter Up And Running ???? So Bare With Me Ok, I'am Not Digital At All , More Right Brain If You Get My Drift?/ Ok So Here Goes , Set Points 1.0 1.2 1.4 And 1.6 All Represent A Precentage Of 02 In The Breathing Loop ? Right Ok , Now 1.0 = 21% Of 02 1.2 = 32% To 36% 1.4 = 50 % And 1.6 = 95% To 100% Of Oxygen . Am I Right So Far ??????? No , Ok So You Can See Where I'am Going With This , I Want To Know What These Numbers Represent In Precentage Of Oxygen In The Breathing Loop , And What To Expect To See On The Meter When Its Up And Running ???? I Signed On Here To Be Learned Ok So Keep It Simple . I Doin't Understand Geek Speak Thanks Bbb

wedivebc

I think the numbers you are looking for are partial pressure of oxygen represented in atmospheres absolute. 1.0 = one atmosphere of O2 or equivalent of 100% oxygen at the surface. When you delve into the CCR world you no longer think in terms of fraction of gas or percentages.

__________________
Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

Packhorse

To work out the PPO (partial Pressure Oxygen) multipy the % of O2 in the mix by the depth in atmospheres.
21% at surface = .21 X 1ata = .21ppo
21% @ 30meters = .21 X 4ata= .84ppo
100% @ 6meters = 1.00 X 1.6 ata = 1.60ppo

If you have done a nitrox course you should already know this.
If not or if you need a refresher check out this link

Nitrox FAQ

__________________
There are no stupid questions, but there are a LOT of inquisitive idiots.

bluedjango1

wasn't this covered in OC Openwater??

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Safe diving,
Corey

kybrt

probably going to fly one of those soda bottle jobs......

__________________
Marv


Fidelis Ad Mortem
www.diveboatkaren.com

duffmiver

I would strongly suggest you take a break from building rebreathers and get some training before someone gets hurt.

Abbo

Partial pressure is the part multiplied by the pressure.
If you have a can of Nitrox 20% and take it down to 40m (where the pressure is 4+1=5ATA), the partial pressure is 20% of 5 atmospheres, or 1 ATA. That's the same as sitting on the boat at 1 ATA and breathing 100% oxygen (at least, as far as the effect of the oxygen goes anyway).

The reason is that your body only cares how many oxygen molecules it gets, not what they're mixed with. Imagine you're walking onto a dance floor and are feeling lucky. There are 21 beautiful ladies there, and that's all you can see: it doesn't matter what the other 79 are - men, dogs, cats, whatever. Now assume your doctor told you you needed one of those ladies every hour: it doesn't make any difference at all to you whether the dance hall is taking in one lady and 4 men every hour or just the one lady - you just have to have your lady. It makes a lot of difference to the composition of the dance floor though.

divetheworld

The most fundamental part of closed circuit rebreathers is the constant PO2 diving. This gives a dynamic loop mix dependant upon the depth (pressure) of the breathing gas.
Example;

Setpoint0.7
depth (m) mix (%)
16...............27
18...............25
20...............23
22.............. 22
24.............. 21
26.............. 19
28.............. 18
32.............. 17
34.............. 16
36.............. 15
40.............. 14

You can see the mix in the loop changes with depth but the PO2 remains at 0.7
0.7 at the surface is 70% oxygen. .7 is the low setpoint on most ECCR rebreathers.

Re-illiterating the comment above, training is absolutely required as this is life critical. This is only one aspect of CCR training that your life will depend on.
Because I feel the need to make this point bold to you, please try to work out the following;
Your at 50m diving a setpoint of 0.7 , you now ascend to the suface without changing your gas mix. What will you be breathing at the surface?







answer: you wont be breathing, you will have passed out from hypoxia and possibly drowned.

Although this may seem like it was designed to just scare you (which it was) the dynamic gases in the loop require a lot of knowledge and muscle memory when making the most dangerous part of your dive, the ascent.
Some mixes will sustain you at depth quite happily, but an ascent to th esurface on such mixes can leave too little oxygen in your body to sustain life at a cellular level. In such cases there is nothing that can be done to revive the casualty. not even oure oxygen ventilation.

I hope we are giving you pause for thought.


Brent

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OceanOpportunity

On a CCR, 'setpoint' refers to your desired PO2. This is irrelevant of your fraction of gas used with your diluent. For just starting out, you will likely use a diluent gas of air. Yes, its FO2 is a constant of .21, however its PO2 increases with increased depth. Your 'setpoint' for CCR diving is usually set at .7 to 1.4. To make up this PO2 in your breathing loop, this consists of the PO2 of your diluent at depth, plus the pure oxygen added by the unit to reach your desired setpoint. As you metabolize the oxygen, more O2 is added to maintain your desired setpoint.

So, in short, setpoints (PO2's) and FO2's are two different animals.

__________________
Michael Lombardi
Oceans of Opportunity
www.oceanopportunity.com

Elected Director, Society for Human Performance in Extreme Environments

MN'07, The Explorers Club

Project Manager, Diving a Dream

big bootie bottom

BRENT, THIS IS WHAT I WAS LOOKING FOR THANK YOU .now things are staring to clear up , I was always wondering why the dive tables were so much differant for rebreathers. as far as training ,yes yes I agree 100% , the reason for the question ??? was to ferther this process for me .after all I thought that was what this site was all about , anyway I'll bet a lot of newbees have thought about this same question and were afraid to ask, so I'am the dumb bastard that just had to ask LOL. for myself I find it hard to go much below 40m and have not done so in many year ,the reason I became interested in rebreathers is size & weight ,a whole weekends diving in a 40# package.the training that I 've looked at usually comes with a manufactors uinit that I don't like, no names here please, ever one here has his or her preferrance ,as for homebuilt & training they don't go well together when one goes into the LDS and I'am not talking church, well maybe for some ??? the other Is I have the shop tools to do the job & the ability & while I'am not in any way a excelent machinst ,I can . reason 3 $$$$$ most manufactured rebreather cost more than I paid for my intire boat motor sails . thanks to all for the help , and like the man says...I'll be back see ya.