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Thread: IP pressures for O2 and dil regs

  1. #31
    RBW Member cb1 is an unknown quantity at this point cb1's Avatar
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    rEvo iii

    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by NickB  View Original Post
    Without the environmental seal and pressure transmitter, the IP still increases, but in line with the increase in ambient pressure. With it, it over-compensates, increasing the differential in the IP.
    Another query on this. If there is IP over compensation using an environmental seal and pressure transmitter as you say, then would 2nd stage regs using environmentally sealed 1st stages not free flow at a certain depth due to this over compensation?
    Last edited by cb1; 6th February 2018 at 17:31.

  2. #32
    RBW Member Dive Africa is an unknown quantity at this point Dive Africa's Avatar
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    Re: IP pressures for O2 and dil regs

    Ok a little bit of a high-jack - but how do you deal with O2 IP on a 150m/500ft dive? yes I do dive that deep (from time to time) so its a legitimate question.

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    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by Dive Africa  View Original Post
    Ok a little bit of a high-jack - but how do you deal with O2 IP on a 150m/500ft dive? yes I do dive that deep (from time to time) so its a legitimate question.
    Plug in rich BO to offboard addition block and use that when below the O2 cutooff depth.

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  4. #34
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    rEvo iii

    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by Dsix36  View Original Post
    Plug in rich BO to offboard addition block and use that when below the O2 cutooff depth.

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    Just curious how many people use this method for deep dives and how do they rate this method.
    Cheers


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  5. #35
    RBW Member techintime is an unknown quantity at this point techintime's Avatar
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    Re: IP pressures for O2 and dil regs

    Been a while since I have been on this forum so please pardon the resurrection of this thread. There is a lot more to the subject of the O2 DS4 IP setting and the impact/dangers of staying in the balanced (metal cap off) versus unbalanced (metal cap/environmental seal on) configuration. There are a couple of other threads such as the one attached below. But in short for an HCCR capable Revo:

    Standard HCCR mode: (Metal cap on, orifice unplugged, IP set to 11bar) the O2 regulators ability to supply O2 is going to start trailing off passing about 90m and is going to shut down completely by NLT 110m. Thats the theoretical limit and it wil probably shutdown earlier due to internal friction. Once below the shutdown depth, it will be unable to supply O2 by any means...not by selenoid, not by manual addition, not by orifice.
    Note: the manual recommends setting the IP to 12bar, but from my experience and that of two other friends diving REVOs, you are likely to have the overpressure valve on the O2 DS4 leak and the IP may also creep high. I have found 11-11.25bar to be a more stable, better setting.

    If you modify the machine to run as an ECCR (metal cap and seal removed, orifice blocked) then the DS4 will be "balanced" and will be capable of supplying O2 at any conceivable depth via the solenoid or manual addition. You must block the orifice. Otherwise the increased density of the flow through the orifice caused by the balanced DS4 will supply an ever increasing amount of O2 as depth increases which will far exceed that metabloized. If the orifice is not blocked, the PPO2 will be spike high and be unmanageable at depth. I also recommend setting the IP to 9bar to reduce the loading on the DS4.

    Concerning how I dive...here is my personal technique. Opinions vary...and this one is mine.

    My technique for dives up to 80m is to go HCCR

    My technique for dives deeper than 80m is go ECCR because it keeps automatic functions working and keeps exactly the same habit patterns.

    Concerning running the machine in HCCR and plugging an balanced rich Bailout into the MAV and using manual addition. A lot of people do it, but I dont like it. Again my opinion, but as I see it, this requires a change of habit patterns to go to manual addition, which is risky. Also, there is no automatic O2 addition to maintain PO2 if the diver is negligent, or distracted by a problem. The REVO has a lot of technology designed to automatically keep the breathing gas correct...why deliberately defeat the technology and turn the machine into low tech MCCR. Also, the manual addition of O2 at depth can be very tricky. it doesn't take much of a push to go way over the amount needed. Also, on the initial ascent, prior to the DS4 waking up, there is a huge risk of hypoxia because the habit patterns are completely opposite of a normal ascent on ECCR or HCCR. Think about it. On a normal ascent you are venting loop volume and the machine is working overtime to put O2 into the loop as the PO2 falls due to decreasing pressure. The last thing you are doing on a normal ascent is manually adding gas to the loop. So if you are ascending from depth with an O2 DS4 that cant give you any O2 by any means then you have to add O2 manually at the same time you are venting unneeded loop volume and you also have dropping PO2 due to the decrease of pressure. This is a weird situation not encountered in any other part of CCR diving. I ran the numbers on this and depending what the actual PO2 is in the loop at the start of the ascent, it only takes 20-25m (2-2.5 min) of ascent for the PO2 to drop to hypoxic levels and lose conscience if the diver is inattentive. The initial ascent is a very busy time which increases the chance of an inattention mistake and is especially dangerous when the habit pattern is opposite of normal diving.

    Another thing to consider on plugging in a rich bailout and using it to control PO2. If the HE to N2 ratio is different than what you have in the diluent then you will have a different inert gas ratio in the loop than your computer thinks. This can lead to inaccurate decompression profile, narcosis, DCS, maybe even a counter-diffusion hit.

    My two cents...take it or leave it.

    http://www.rebreatherworld.com/showt...rid-mode/page2

  6. #36
    RBW Member cb1 is an unknown quantity at this point cb1's Avatar
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    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by techintime  View Original Post
    Been a while since I have been on this forum so please pardon the resurrection of this thread. There is a lot more to the subject of the O2 DS4 IP setting and the impact/dangers of staying in the balanced (metal cap off) versus unbalanced (metal cap/environmental seal on) configuration. There are a couple of other threads such as the one attached below. But in short for an HCCR capable Revo:

    Standard HCCR mode: (Metal cap on, orifice unplugged, IP set to 11bar) the O2 regulators ability to supply O2 is going to start trailing off passing about 90m and is going to shut down completely by NLT 110m. Thats the theoretical limit and it wil probably shutdown earlier due to internal friction. Once below the shutdown depth, it will be unable to supply O2 by any means...not by selenoid, not by manual addition, not by orifice.
    Note: the manual recommends setting the IP to 12bar, but from my experience and that of two other friends diving REVOs, you are likely to have the overpressure valve on the O2 DS4 leak and the IP may also creep high. I have found 11-11.25bar to be a more stable, better setting.

    If you modify the machine to run as an ECCR (metal cap and seal removed, orifice blocked) then the DS4 will be "balanced" and will be capable of supplying O2 at any conceivable depth via the solenoid or manual addition. You must block the orifice. Otherwise the increased density of the flow through the orifice caused by the balanced DS4 will supply an ever increasing amount of O2 as depth increases which will far exceed that metabloized. If the orifice is not blocked, the PPO2 will be spike high and be unmanageable at depth. I also recommend setting the IP to 9bar to reduce the loading on the DS4.

    Concerning how I dive...here is my personal technique. Opinions vary...and this one is mine.

    My technique for dives up to 80m is to go HCCR

    My technique for dives deeper than 80m is go ECCR because it keeps automatic functions working and keeps exactly the same habit patterns.

    Concerning running the machine in HCCR and plugging an balanced rich Bailout into the MAV and using manual addition. A lot of people do it, but I dont like it. Again my opinion, but as I see it, this requires a change of habit patterns to go to manual addition, which is risky. Also, there is no automatic O2 addition to maintain PO2 if the diver is negligent, or distracted by a problem. The REVO has a lot of technology designed to automatically keep the breathing gas correct...why deliberately defeat the technology and turn the machine into low tech MCCR. Also, the manual addition of O2 at depth can be very tricky. it doesn't take much of a push to go way over the amount needed. Also, on the initial ascent, prior to the DS4 waking up, there is a huge risk of hypoxia because the habit patterns are completely opposite of a normal ascent on ECCR or HCCR. Think about it. On a normal ascent you are venting loop volume and the machine is working overtime to put O2 into the loop as the PO2 falls due to decreasing pressure. The last thing you are doing on a normal ascent is manually adding gas to the loop. So if you are ascending from depth with an O2 DS4 that cant give you any O2 by any means then you have to add O2 manually at the same time you are venting unneeded loop volume and you also have dropping PO2 due to the decrease of pressure. This is a weird situation not encountered in any other part of CCR diving. I ran the numbers on this and depending what the actual PO2 is in the loop at the start of the ascent, it only takes 20-25m (2-2.5 min) of ascent for the PO2 to drop to hypoxic levels and lose conscience if the diver is inattentive. The initial ascent is a very busy time which increases the chance of an inattention mistake and is especially dangerous when the habit pattern is opposite of normal diving.

    Another thing to consider on plugging in a rich bailout and using it to control PO2. If the HE to N2 ratio is different than what you have in the diluent then you will have a different inert gas ratio in the loop than your computer thinks. This can lead to inaccurate decompression profile, narcosis, DCS, maybe even a counter-diffusion hit.

    My two cents...take it or leave it.

    http://www.rebreatherworld.com/showt...rid-mode/page2
    Well argued, I agree completely.

    Cathal

  7. #37
    RBW Member steveg is an unknown quantity at this point steveg's Avatar
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    Re: IP pressures for O2 and dil regs

    I have used offboard method a few times, never plugged orifice so far. Works well. By "rich BO" I understand say a 50% nitrox. Keep it simple.



    As for a He or N2 fraction of the gas, depending on the fraction of said gases and ratio of bottom time to overall runtime, it could well be negligible in terms of deco obligation. Correct me if I'm wrong?



    It takes some time before po2 goes from a 1.3 (or whatever you're using) to hypoxic unless you have a problem and forget it completely (and ignoring all the flashes on HUD, controller, etc.). That's where your manual training comes in.



    Once I find the plug I will likely try with a plugged orifice too


    Thanks,
    Steve

  8. #38
    Supporting Member Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36's Avatar
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    Defender Optima Dolphin

    Re: IP pressures for O2 and dil regs

    Something else to consider. Once you are actually deep the loop p02 will decrease extremely slow, slower the deeper you go. Chances are that from 400' down to 600' and a few minutes at depth will only require one extremely short burst of rich dil.

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    Quote Originally Posted by kwinter  View Original Post
    I could just be blowing smoke out my butt.
    Quote Originally Posted by kwinter  View Original Post
    And note the wisdom from DSix36
    MY ADVICE AND POSTS ARE WORTH EXACTLY WHAT YOU PAID FOR THEM!!!!!!
    POLITICAL CORRECTNESS IS SO YESTERDAY AND I AM DONE WITH IT!!!!!

  9. #39
    RBW Member techintime is an unknown quantity at this point techintime's Avatar
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    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by steveg  View Original Post
    I have used offboard method a few times, never plugged orifice so far. Works well. By "rich BO" I understand say a 50% nitrox. Keep it simple.



    As for a He or N2 fraction of the gas, depending on the fraction of said gases and ratio of bottom time to overall runtime, it could well be negligible in terms of deco obligation. Correct me if I'm wrong?



    It takes some time before po2 goes from a 1.3 (or whatever you're using) to hypoxic unless you have a problem and forget it completely (and ignoring all the flashes on HUD, controller, etc.). That's where your manual training comes in.



    Once I find the plug I will likely try with a plugged orifice too


    Thanks,
    Steve
    I think that some people just don't like the idea of modifying their machines. I think it makes some people nervous to be removing caps on DS4s and changing IP settings, etc. It made me nervous the first time I did it too. There is a comfort in leaving it alone. My technique on the ramp up to a deep dive requiring ECCR is to mod the machine a weekend or two prior to give it a few test dives in ECCR to make sure all is well.

    Also, concerning the HE/N2 fraction if using a "rich BO" such as a 50% for use in maintaining PO2 at depths below the DS4 shutdown...You are right that the DCS threat is probably not much of a factor. The N2 is more forgiving than the HE in terms of decompression profile until some ridiculous depth ( I cant remember what) but the narcosis issue could be significant. Each shot of a 50% bottle will be adding N2 to the loop at depth. We select the HE fraction in the diluent for one reason only...to manage the narcosis on the bottom. So after all the careful calculations to design of the perfect Trimix in the diluent...the first shot of rich BO to adjust PO2 throws it all out the window. And the N2 fraction will continue to rise with each manual addition and so will the narcosis. No way around it. All of this can be avoided by the simple, 10-minute ECCR mod. It's really easy and the only extra tool you need is a gauge to set the IP (which every CCR diver should have anyway).

    Again...people can dive how they want, but I think that decisions like this should be made with a full understanding of what is happening.

  10. #40
    RBW Member steveg is an unknown quantity at this point steveg's Avatar
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    Re: IP pressures for O2 and dil regs

    Quote Originally Posted by techintime  View Original Post
    Again...people can dive how they want, but I think that decisions like this should be made with a full understanding of what is happening.

    Absolutely!



    I plan dil to be ~1.1 at max depth, and found I need little in the way of offboard addition to maintain po2.


    However as you said, it is of utmost importance that you are (VERY) familiar with the setup you're diving, how it works and what to do if it screws up.


    Thanks,

    Steve

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