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Thread: pool/training mode

  1. #1
    RBW Member moteman is an unknown quantity at this point moteman's Avatar
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    pool/training mode

    This might be a really stupid question, but I'm going to ask it anyway. I have a Petrel that came with my Optima. Because the low setpoint is .50 PPO2, pool training burns thru a lot of oxygen and results in the CL's being constantly full and venting, making buoyancy control hard to maintain. A more appropriate mix for training in a pool might be closer to .25-28 PPO2 (depending on pool max depth). Is there anyway to lower the setpoint to .25 PPO2 or would I be better off running it on manual and closely monitoring it?
    Last edited by moteman; 18th September 2017 at 19:04.

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    RBW Member rjack will become famous soon enough rjack will become famous soon enough rjack will become famous soon enough rjack's Avatar
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    Re: pool/training mode

    There is no reason to run with less than 100% anywhere while shallow - whether in the pool or outside on a "real" dive. Realistically ppO2 is going to be 0.9 to 1.1 because there's leftover air in the loop.


    Yes if you go up and down you are venting nearly pure O2. All the more reason to practice not going up & down :)

  3. #3
    Hammerhead CCR diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike has a reputation beyond repute diverklondike's Avatar
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    HammerHead CCR

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    Re: pool/training mode

    Note that I am not an instructor so take this comment for what it's worth....

    I know that some people specifically use a dil with a higher PP02 for exactly the reason that you mentioned when doing pools drills.

    Just make sure that you label the % O2 properly to ensure that you don't make a mistake on a future dive when something else would be more appropriate.

    Just my 2 cents...

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    RBW Member broncobowsher is on a distinguished road broncobowsher is on a distinguished road broncobowsher's Avatar
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    Re: pool/training mode

    Quote Originally Posted by diverklondike  View Original Post
    Note that I am not an instructor so take this comment for what it's worth....

    I know that some people specifically use a dil with a higher PP02 for exactly the reason that you mentioned when doing pools drills.

    Just make sure that you label the % O2 properly to ensure that you don't make a mistake on a future dive when something else would be more appropriate.

    Just my 2 cents...


    I read this at lunch today and thought about it in the afternoon. My thoughts were if the DIL was filled to about the setpoint you could bounce around doing drills and just go through that without having wild swings of PPO that would cause the controller to go wild trying to correct.


    Sounds like you are advocating what I was thinking of.


    You will still blow through the DIL, but the O2 side should hardly be touched.

  5. #5
    Dave Tomblin wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc has a reputation beyond repute wedivebc's Avatar
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    Re: pool/training mode

    you should be practising minimal or optimal loop volume and should have no trouble whatsoever maintaining 0.5. As an instructor I would never advocate a low setpoint in a pool. No need for it.
    Cheers,

    Dave....

    www.wedivebc.com

  6. #6
    Chett Lehrer Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L has much to be proud of Chett.L's Avatar
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    rEvo FT / Hollis P-2/ rEvo lll

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    Re: pool/training mode

    Make sure you have a person watch and follow you around topside while your in the pool.

    Best regards,
    Chett. L

  7. #7
    RBW Member DeathBoxDiving is an unknown quantity at this point DeathBoxDiving's Avatar
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    Re: pool/training mode

    +1 for training with high PO2. I also use the diluent gas I would be using in the ocean.

    If you cannot maintain control in a pool where the column it's relatively still imagine the problems you'll have during your last stop in the ocean.

    Just my .02

  8. #8
    RBW Member AndrewDonn is on a distinguished road AndrewDonn is on a distinguished road AndrewDonn's Avatar
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    Re: pool/training mode

    I used to think something along these same lines back when I fist got into rebreathers years ago and had a few discussions of this very topic with some of the manufactures advocating for a low set point option. Universally their reply was that it would be a recipe for disaster. I was unconvinced at the time but have since come around to their way of thinking. In my case it was just open circuit mentality. A .21 setpoint would just be the same as air after all and we have all dove air, right? Problem is a rebreather isn't OC. On OC your "setpoint" at the surface has no where to go but up. At the surface on a rebreather your PPO2 has no where to go but down and if you only start at .21 you will find yourself unconscious quick. We think of pool training as safe but very shallow water is actually the most dangerous region for a rebreather. The changes in pressure, volume and density are the most dramatic and the control system has the hardest time keeping up. When we first jump at the start of a dive we go from a workload of essentially zero to one of exertion. Add in a burst of low oxygen concentration diluent and the PPO2 plummets. If you started at a setpoint of .21 the O2 injection system just couldn't add O2 fast enough to keep you from going lights out.

    Actually there was an incident years ago at one of the major trade shows the year one of the first commercial rebreathers first came out. They set up a try-dive in a big swimming pool and had a bunch of people pass out because they were using air diluent. It was luck they didn't kill someone.

    Like others have advocated, use a high O2 diluent for any shallow training and don't be afraid to pump The O2 in your loop up to close to 100% before you jump for any dive.

  9. #9
    RBW Member Mr.Dave is an unknown quantity at this point Mr.Dave's Avatar
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    Re: pool/training mode

    An experienced RB diver passed away in the shallows (<2m) this summer in Cyprus, although no one has confirmed cause, Hypoxia is a real concern. The incident really made me question my approach to shallow diving and highlighted the risks. 100% O2, ADV isolated reduces risks.

  10. #10
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    Re: pool/training mode

    Quote Originally Posted by moteman  View Original Post
    This might be a really stupid question, but I'm going to ask it anyway. I have a Petrel that came with my Optima. Because the low setpoint is .50 PPO2, pool training burns thru a lot of oxygen and results in the CL's being constantly full and venting, making buoyancy control hard to maintain. A more appropriate mix for training in a pool might be closer to .25-28 PPO2 (depending on pool max depth). Is there anyway to lower the setpoint to .25 PPO2 or would I be better off running it on manual and closely monitoring it?
    FWIW, for pool sessions, I just use air dil. The O2 usage goes up, yes but once the unit settles at setpoint (0.7 for me), it's no more than usual. I help it out usually by getting it settled at 0.7 whilst I'm getting in and manually adding O2 (so like a bad O2 flush) if I need to. PPO2 is then always somewhere at or above 0.7. Yes, it makes the buoyancy control a bit more work but then practice is the reason left for using it in the pool anyway for me (once any changes/fixes have been proven). As has been posted elsewhere on this thread, the shallows are where you need to be really switched on and things change fast.

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