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Poseidon mk6

Discussion in 'Rebreathers Closed and Semi Closed Circuit' started by Joe, Apr 4, 2015.

  1. barrygoss

    barrygoss Active Member

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    One set of "rules" regarding Sorb to live by.
    from here - http://lists.drogon.net/inspiration/zorg.html

    "From gordon@drogon.net Tue Apr 29 20:40:02 2003
    Date: Thu, 10 Apr 2003 15:34:54 +0100 (BST)
    From: Gordon Henderson To: inspiration@drogon.net Subject: Greetings from planet Zorg...

    Here on Zorg, we abducted some humans to test your resistance to CO2 and the efficiency of our patented CO2 grabbing demon chamber. We took a human and connected a hose to them. The hose supplies gas and has one-way valves. The exit of the hose goes into a box. Inside this box are 1000s of little demons. These demons adore CO2. They will grab a passing molecule of CO2 and hang onto it for the rest of their lives. They can only hold one each. After the CO2 demon box there is another box with different demons inside - these count the number of O2 molecules you have used and replaces them. We observed that humans when in a steady state consume the same amount of O2 per breath, regardless of the pressure we subjected them to. When given 100 molecules of our gas, they would use 4 molecules of our oxygen and turn this into 3 molecules of CO2 and 1 molecule of water vapour. So in the test, with 100 molecules of gas in the loop. The human push/pulled this through the box with the CO2 demons in it. Every breath, 3 lucky demons grab a CO2 molecule each and are happy for the rest of their lives. We repeated this for many of your earth hours, pushing 100 molecules of gas through the CO2 box at a nice steady rate - the happy demon front line progressed linearly through the CO2 demon box until eventually they are all happy. At that point, the loop gas has some CO2 in it and we observed that the humans started to show signs of unease, panic and general ill-feeling. They eventually died a rather uncomfortable death.

    To continue our experiments, we abducted more humans and carried on, this time we subjected them to a pressure of 2 bar. This is the same as being under 10 metres of your water. There is now 200 molecules of gas in the loop, but the human still only uses 4 molecules of O2 and turns these into 3 molecules of CO2 and 1 water vapour. Each breathe pushes 200 molecules through the CO2 demon chamber, so the demons have to work faster to grab the CO2 molecules and die happy. Sometimes a front-line demon misses, but the 2nd line catches it OK. This carries on and eventually all the demons are happy, then as above, the human dies painfully and horribly from CO2 poisoning.

    We needed to do more experiments, so we continued with our abduction programme. Now we're testing to 90m. There are now 1000 molecules of gas in the loop, but as observed before, then humans still only take 4 molecules of O2 out and metabolises these into 3 of CO2 and one of water with each breath, However, the poor CO2 demons now have 1000 molecules of gas going through their chamber like a hurricane, and in those 1000 molecules there are still only 3 molecules of CO2! It's now very hard for the demons to catch a CO2 molecule and hang on to it! The front-line demons have a real hard time catching the CO2 molecules and a lot more pass further down the line to be caught by the latter ones. Eventually, the front-line demons are full, but still the latter ones need to work to catch the CO2 and there will come a stage where there aren't enough latter ones who can catch the CO2 fast enough, so some will get through.

    Eventually so many will get through that the human starts to notice it and dies horribly as before - even when there are still some unhappy and empty CO2 demons left. Continuing our experiments with more abducted humans, we test again at 90m, but then we decide to ascend the human to some depth where the number of molecules in the loop is much less, so each breath the CO2 demons have more of a chance to catch the CO2 molecules left.

    Eventually, after 100's of trials, killing a great many humans every time, (And you should have seen our abduction budget! Off the scale!) we have come up with some rules for keeping humans alive and maximising the happiness of the CO2 demons. Our rules are many, long and complex but to simplify them for you humans we have reduced them to 3 simple rules..

    Rule 1: You have 3 hours maximum.
    Rule 2: For subsequent dives deeper than 20m: You must leave the bottom when the _total_time_ breathed through the system reaches 140 minutes.
    Rule 3: For subsequent dives deeper than 50m: You must leave the bottom when the _total_time_ breathed from the system reaches 100 minutes.

    I'm glad the Inspiration was machine tested at DERA. Glad I wasn't the human being killed every time. I wonder what other rebreathers would show given the same tests? I wonder why others don't bother with these tests, and instead resort to cycling in the garage with a unit on their backs. It's fairly obvious from reading above that things happen differently at depth. The deeper you go, the wider the reaction front becomes and eventually you'll run out of scrubber before the reaction front reaches the end. On my first hit, I was on my 2nd 60m dive with the same scrubber. First had been 60m for 30 minutes and about 60 minutes of deco. Second was 60m for 30 minutes... Thats 20 minutes at depth too many. (3rd rule) Combine that with an increase in breathing rate and workload and bingo, I got a hit. You can not do 2 x 30 minute, 60m dives on the same scrubber without violating the rules. Enjoy, Gordon"

    and if you want to know what that reaction front looks like http://johnclarkeonline.com/2011/10/06/a-look-inside-rebreather-scrubber-canisters-part-1/
    Picture6.png

    So although theoretically your maths stands up, you haven't considered the gas / scrubber in use. (and if put your assumptions into practice a CO2 hit is waiting)

    B
     
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  2. Dave Whitlow

    Dave Whitlow Well-Known Member

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    You are very wrong and this is why they do the CE testing in 'realistic' conditions rather than on on a calculator or on the Internet!

    You are assuming steady breathing and a linear consumption of lime with relation to time, as you would gas from a cylinder. That is not the case. There are papers on the Internet illustrating the non-linear reaction front in the lime. At depth the scrubber is less effective due to gas density because of the reduced probability of a CO2 molecule colliding with the lime, as it needs to to react. In addition, there are times when you exert yourself and the scrubber does not cope and CO2 passes through the lime, and joins the incoming gas.

    I think you will find this explains the process rather well http://lists.drogon.net/inspiration/zorg.html

    When they rate the scrubber for 3 hours that is based a measurements taken in conditions designed to simulate a diver underwater breathing air at 40m in 4c water and producing 40lpm of CO2. AP are proud of their ANSTOI machines and invite factory tours http://www.apdiving.com/en/about-ap/rd-test-centre/

    Yes, I do sometime run my scrubber for over 3 hours but only when the 'overtime' will be relatively shallow. For a deep dive, where the scrubber will be relatively ineffective for the bottom phase of the dive, a new stack is the only sensible option! I have felt the beginnings of a CO2 event (working too hard) and I didn't like it. I am worth more than £8 of lime!
     
  3. Dave Whitlow

    Dave Whitlow Well-Known Member

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  4. clique

    clique Active Member

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    Is the reason I'll stick to the 3hrs which AP say my scrubber is rated to. Perhaps it could last longer and I throw away unused lime, but for the sake of a couple of quid I'd rather avoid the problem entirely.

    All the best,

    Mike
     
  5. Joe

    Joe Active Member

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    Thanks guys I do under stand what your saying. I never said I would be deep at anywhere near 5hrs. Poseidon say fill your O2 cylinder to 135 bar that's 135 x 3 = 405 lts of O2 X 80% that's 324 lts Co2 what I said was on average I use 1.2lts of O2 per min X 80% = 1lt Co2 per min. I think a fresh scrubber can take up 390lts of Co2 so I think if I use 120 bar of O2 for 5hrs of diving the scrubber would still have a reserve. I do know of divers doing 100/130mt dives with 5/6hr runtimes I know most of that time will be at sallow depths doing deco. my normal use of a scrubber be say 2 dives 25/40 mts of 75 min each then maybe a 10mt 75 min dive I have not had any bad effects from this
     
  6. Wibble

    Wibble Fish don't talk
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    Just checking a number: 40 litres/min of CO2 -- did you mean 4 l/min?
     
  7. Joe

    Joe Active Member

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    this is from Poseidon web site (
    Each canister has been tested for a duration of 180 minutes at 40 m/131 ft, water temperature of 4°C / 39,2°F, and a breathing rate of 40 lpm producing 1.6 liters CO2 per minute at STPD (Standard Temperature & Pressure , Dry in accordance with EN14143)
     
  8. Dave Whitlow

    Dave Whitlow Well-Known Member

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    I meant what he said, as this is the standard test they use to measure scubber performance.
     
  9. Wibble

    Wibble Fish don't talk
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    Gosh, 40 litres per minute of CO2 is one hell of a test for them little scrubber daemons!

    I suppose it's to do with clearing a peak of CO2 rather than the 'normal' CO2 production rate?
     
  10. Dave Whitlow

    Dave Whitlow Well-Known Member

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    It is a breathing rate of 40lpm producing 1.6lpm CO2

    This is plenty of capacity for normal diving. Working hard for a sustained period, especially deep, might exceed that. The need to avoid hard work underwater is a good justification for additional safety equipment, such as a scooter, to ease the pain of getting down the shot-line with a current running, or swimming against a current rather than ending the dive.

    A CO2 sensor is another choice for detecting acceptable CO2 level has been exceeded, although that alerts rather late so avoidance is a better plan.
     
  11. Joe

    Joe Active Member

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    this is an old video but bill stone clearly says a min 3hrs more if you use less 02
     
  12. barrygoss

    barrygoss Active Member

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    As pointed out before, your maths is theoretically correct. (also note all the figures you're using are based on the pre-packed scrubber, they have a known packing density, a defined layout and no chance of channelling) you're using a self pack now (tecme?) so how's your packing? is it as good as the robot who packed the pre-packed scrubber all your units testing has been done on?
    is it tighter (more WOB, more chance of generating more CO2 as you're working harder just breathing)
    is it loose? (chance of channelling and as it's looser, there's less lime in there, so duration is reduced)
    With the self pack, you're introducing a whole heap of variables (who taught you how to pack the self pack?) hence, ZORG rules came about and although it's made light of in Gordon's post, they did actually come about from many RB divers deaths.

    rule 1; don't push the scrubber

    B
     
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