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Thread: % asked for Oxygen

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    RBW Member James Appel is an unknown quantity at this point James Appel's Avatar
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    % asked for Oxygen

    When entering the % oxygen asked for (on the Classic Inspiration), the manual says it wants the % in the mixing chamber, not the % in the cylinder (Ok I under stand how to check on what % is in the mixing chamber).

    But I was wondering, if you get a real good flush, WHY wouldnt the % in the mixing chamber be the same as that in the bottle. And if not (i.e. I dont get a 100% flush), it seems that this value would be variable and change each time I tried to flush and read what the % is in the mixing chamber as I would never really be able to flush exactly the same amount or precentage each and every time (ie if I cant get a 100% flush, there will always be a small amount of regular air in the mixing chamber).

    I have been entering the % of oxygen in the cylinder (but then again I dont dive to the limits, and always keep to rec dive limits).

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    RBW Member GuyW has a spectacular aura about GuyW has a spectacular aura about GuyW has a spectacular aura about GuyW has a spectacular aura about GuyW has a spectacular aura about GuyW's Avatar
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    Re: % asked for Oxygen

    James, you are correct.

    there are two things to consider:
    1. The O2% in the cylinder
    2. The completeness of mixing in the head during calibration.

    Neither are 100%. So to correct for this you put in your best guess / measurement of what O2% is being used as the basis for calibration.

    In order to establish this you need to know what O2% is in the cylinder. If you can determine this then calibrate the unit normally with this O2% and then give the unit a really-really good flush and let it stabilize for a while so you are sure that the head contains 100% what is in the cylinder. See what the unit reads. If it is different to what you calibrated for then adjust the calibration number accordingly.

    This "magic number" then corresponds to your typical gas quality and mixing completeness on calibration.

    Or just use 98% like I do.

    Guy

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    Re: % asked for Oxygen

    Quote Originally Posted by James Appel
    When entering the % oxygen asked for (on the Classic Inspiration), the manual says it wants the % in the mixing chamber, not the % in the cylinder (Ok I under stand how to check on what % is in the mixing chamber).

    But I was wondering, if you get a real good flush, WHY wouldnt the % in the mixing chamber be the same as that in the bottle. And if not (i.e. I dont get a 100% flush), it seems that this value would be variable and change each time I tried to flush and read what the % is in the mixing chamber as I would never really be able to flush exactly the same amount or precentage each and every time (ie if I cant get a 100% flush, there will always be a small amount of regular air in the mixing chamber).

    I have been entering the % of oxygen in the cylinder (but then again I dont dive to the limits, and always keep to rec dive limits).
    john,

    first,I have only seen 1 unit that the percentage entered equaled the analyzed gas, and this unit had an IP above the recommended setting..

    on most units its a 1-2% "error", once you find your number it will be consistent as long as you dont do anything to the solenoid or change the IP..

    tosee how accurate you are calibrating it will take a few steps.. first you really need to know what the actual ambient pressure is and a good gas analysis.. I wouls start with 1% less on the oxygen and as close to the ambient pressure as possible.. no cal the unit as normal.. no we haveto verify it..

    you need to get 100% in the loop.. expect to use alot of oxygen.. You have to do complete flushing.. start with one complete flush, (suck the loop to negative them fill til the opv vents..suck some more gas out and force gas from the exhale inhlale side through to the exhale side.... sucj the loop dry and do it again.. repeat 4 to 5 times...now we have to get the loop as close to abmient aspossible,make sure the opvis on the lowest settng, and start crushing the inhale counterlung to force gas out.. keep doing this until, you cant vent any more.. If the lungs are still "puffy" vent squeenze both counter lungs.. now look at your handsets if they dont equal ambient pressure multiplied by oxygen percentage (analyzed) the cal is wrong... get some air into the head, and cal again.. keep doing the above procedure until you find out what works then stay with it..
    Joe Radomski
    CCR Trimix Instructor Trainer
    ANDI Instructor Trainer Director #10

    All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

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    RBW Member James Appel is an unknown quantity at this point James Appel's Avatar
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    Re: % asked for Oxygen

    Quote Originally Posted by GuyW
    James, you are correct.

    there are two things to consider:
    1. The O2% in the cylinder
    2. The completeness of mixing in the head during calibration.

    Neither are 100%. So to correct for this you put in your best guess / measurement of what O2% is being used as the basis for calibration.

    In order to establish this you need to know what O2% is in the cylinder. If you can determine this then calibrate the unit normally with this O2% and then give the unit a really-really good flush and let it stabilize for a while so you are sure that the head contains 100% what is in the cylinder. See what the unit reads. If it is different to what you calibrated for then adjust the calibration number accordingly.

    This "magic number" then corresponds to your typical gas quality and mixing completeness on calibration.

    Or just use 98% like I do.

    Guy
    My point is that IF I were to do a complete 100% effective flush, then the % of o2 in the head would be exactly the same as that in the cylinder. So why am I not supposed to enter the % of O2 that is in the cylinder if a complete flush gives me a head that has 100% of whats in the O2 cylinder (which has never been 100% O2, but has varied between 97% - 99% depending on O2 supplier as I always analyze my cylinder contents).

  5. #5
    Moderator jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski has a reputation beyond repute jradomski's Avatar
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    Re: % asked for Oxygen

    Quote Originally Posted by James Appel
    My point is that IF I were to do a complete 100% effective flush, then the % of o2 in the head would be exactly the same as that in the cylinder. So why am I not supposed to enter the % of O2 that is in the cylinder if a complete flush gives me a head that has 100% of whats in the O2 cylinder (which has never been 100% O2, but has varied between 97% - 99% depending on O2 supplier as I always analyze my cylinder contents).
    The way the inspiration does calibration it wouldn''t work.. It does the head flushing.. If you flushed a loop and truely had 100% of your oxygen mix, you would get a cell stuck error on the classic, I'm not sure if the vision gives the same message though..

    You have to understand the way the Inspiration calibrates.. its forcing oxygen across the cells, when it no longer sees a change, it makes that the value and calibrates to that.. The entire loop itself definately does not have 100% in it..
    Joe Radomski
    CCR Trimix Instructor Trainer
    ANDI Instructor Trainer Director #10

    All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

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    RBW Member James Appel is an unknown quantity at this point James Appel's Avatar
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    Re: % asked for Oxygen

    Quote Originally Posted by jradomski
    ................................... You have to understand the way the Inspiration calibrates.. its forcing oxygen across the cells, when it no longer sees a change, it makes that the value and calibrates to that.. The entire loop itself definately does not have 100% in it..
    Thanks, I think I now understand why it isnt really asking for the % in the cylinder, it stops injecting when it reaches a point where the cells are no longer changing, before it reaches 100%. And each rebreather could vary depending on the diffrences in the solenoid, battery, etc.
    Last edited by James Appel; 30th April 2006 at 09:20.

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