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Dil & O2 cylinder sizes

Discussion in 'Rebreathers Closed and Semi Closed Circuit' started by Wibble, Oct 31, 2017.

  1. Wibble

    Wibble Fish don't talk
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    Dumb non-box person question...

    Are 3 litre cylinders "better" than 2 litre cylinders?

    I appreciate that you actually only use the diluent for filling the loop on the bottom; once they're 'filled' then you don't need the diluent except for problems. Similarly the O2 is only required to replace the metabolised O2 (about 1 litre/min???). So therefore there's plenty of gas in 2 litres.

    However, if there's problems, wouldn't having additional gas be a benefit? For instance each time you flush the loop you'd need a fair amount? (Excuse my ignorance, not dived one nor taken any courses)

    Also if you're doing multiple dives, wouldn't 2 litre cylinders mean that you'd need to fill them in between dives?

    Are 2 litre tins that much lighter than 3 litre tins?


    This thought train was brought on by looking at the Red Bare which only has space for 2 litre tins unless modifications are made (the stand needs to be extended and there's only enough space for 'dumpy' 3 litre tins).
     
  2. Dave Whitlow

    Dave Whitlow Well-Known Member

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    Diluent is used is small amounts on the descent and also for filling the wing at the surface so, typically 15-30 bar (in a 3l) is used per dive.

    Diluent flushes can consume large amounts of gas, especially at depth, but a flush is an exception as a response to either high loop ppo2 or to check a cell anomaly.

    Oxygen use depends on the person, and work rate, but is typically 20 bar (in 3l) per hour, with additional oxygen being expended on the ascent, especially at 6m, as some oxygen is discarded with inerts during deco. I also flush the loop with oxygen to force the ppo2 to 1.6 to confirm my cells can read high.

    For most diving done by most people 2l bottles are enough. The need for refills after a few dives is generally resolved by owning multiple bottles (I have 4 sets) or by decanting from a 'bank'.
     
  3. nickb

    nickb Active Member

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    2l cylinders tend to be used on smaller rebreathers: AP Evolution, rEvo micro etc.

    I think that the Sentinel had 2l bottles as a design philosophy, although anything to reduce the burden of lugging one around would have been welcome and this appears to have been carried over to the vastly superior RedBare.

    A short stack Megalodon will often have 2l cylinders too but most CCRs will use 3l tins as these tend to offer the best trade-off between size and convenience.
     
  4. Vanny

    Vanny Active Member

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    Yes what Dave said. I've 3ltr cylinders. On my mix course at Chepstow the instructor used an inspo Evo with 2ltr cylinders and needed to change them/fill , certainly the O2 , between dives. Albeit deep dives. 3ltrs seem to give more flexibility and like Dave I have 2 sets, although 1 sets out of test because I'm tight and lazy.
     
  5. Wibble

    Wibble Fish don't talk
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    Thanks for that.

    The Redbare did seem very nice (to a person with no experience of CCR) although it wasn't as clean around the back as the JJ and Inspiration (when mounted on a third-party frame). Whilst the idea of a JJ with twin 7's a-la GUE configuration seems a little, errm, esoteric, it's the fact that a JJ can be configured like this which is testament to how flexible it is.
     
  6. Vanny

    Vanny Active Member

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    I haven't seen the redbare in the flesh and know very little about it. The inspo in a frame can have any cylinder/valve config which I think is what your getting at with the GUE JJ. I haven't tried bigger than 3's on mine but the general vibe is that anything bigger e.g. 7's are a real heavy pig to dive. So whilst a nice to be able to do in reality fairy inpractical for normal diving. Ben in scapa uses 7's on his meg , my understanding, is due to the amount of wreck penetration he does the larger cylinders become his bail out, so good for a specific purpose.

    Recently I've set mine up to take 2 pairs of 3's , so 2x O2 , one for the unit , one for back up/bail out. 2xdil , usually mix driving the unit the other air for suit/bail. On shallow dives no need for separate bail out on deeper longer dives coupled with 2x7 bailout it improves my bailout choices.

    I think the units stock are all v good. All this dicking about might help or maybe just satisfying my need to tinker. Whilst the AP plastic box isn't v popular I still argue with myself if it was the best compromise, it's certainly a lot lighter than my current set up to shift around, so in time I may just go back to it, for the time being I'm very happy with how my set up dives and works.

    The JJ. Seems to get left pretty much stock , the AP seems to encourage butchering.
     
  7. nickb

    nickb Active Member

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    FTFY
     
  8. Vanny

    Vanny Active Member

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    I larfed so hard snot came out my nose. Thank you
     
  9. Depthdevil

    Depthdevil New Member

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    Hi there. Just joined this forum, and noticed this post. I have limited knowledge of ccr, but have now settled on my unit of choice. The redbare offers virtually all of my wants in a unit. But cylinder size is a niggling little worry. Not for general diving, but the odd scenarios we sometimes find ourselves in. For this reason I am experimenting with some small diameter 4 ltr tins. I’m fortunate to have a spare sentinel, which is my tinkering toy, and it is work in progress. If/when it becomes a regular toy, I’ll post more about it! But the cylinder size does ease my mind somewhat.
     
  10. Wibble

    Wibble Fish don't talk
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    Welcome to the forum.

    I've noticed that quite a few people speak highly of the Sentinel, particularly the Red Bare. Nice to see several of them at Vobster the other day -- which, to be fair, is where they're made.

    How would you compare the Inspiration to the Red Bare?
     
  11. Depthdevil

    Depthdevil New Member

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    Inspo is lighter, but having used large twins for years, I didn’t mind the sentinel being heavier.
    Having a bov which worked was nice, but only had a gg on the classic which never inspired confidence. (Not an ap issue).
    Having co2 on the red head, which seems to work well, was much nicer than the “questionable”, ap version. (Only had 3rd party influence though)
    Closer support to my location played a small part in my decision.
    Off board connections as standard was a bonus, as was Vr computer knowledge from previous years.
    Lastly, ten years advancement on design and development made me feel like I was buying into current thinking, rather than the vision being an older design. Am I happy? Yes. Do I feel as though improvement can be made? Probably. But I feel confident in the redbare configuration to keep with it. Looking forward to the software upgrade in the new year. Only wished it came in blue? But my old cover is nearly modified to fit, so watch this space for the blue bare in mid January.
     
  12. Wibble

    Wibble Fish don't talk
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    Isn't someone doing a carbon fibre cover for the RedBare? It's interesting to see all the third party covers available for the JJ.

    Interesting the difference in the HUD on the RedBare -- a single green light. If it flashes, look at the handset, if it changes colour then it's a potential bailout. Isn't there a second light for deco too? That seems like a change in philosophy from the constant flashing of the JJ/inspiration HUD (caveat here for no experience of either).
     
  13. Vanny

    Vanny Active Member

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    Inspo hud only flashes when something is wrong. Steady green all good red flashing bad. Pretty simple. My mate dives a meg with a constant flashing hud, I don’t like it anddoubt it would work for me.
     
  14. Depthdevil

    Depthdevil New Member

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    Just a note for the Vms hud. Solid green is good. Flashing blue green, check handset for possible problem, and deal with if needed. Flashing red (with buzzer), bail out. There is the option to go back on the loop if the problem was resolved later. White flashing light means you have deco to do.
     
  15. Depthdevil

    Depthdevil New Member

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    P.s. Carbon cover is in existence, but Vms aren’t too happy about the quality yet? (Martin, please correct me or advise if that isn’t correct). The sample I saw suffered from the same issues as previous attempts of forming carbon fibre as I have had. Tight corners and radii stretch the fibres and so it looses its consistent tight weave, and the material appears to be stretched in corners. So I guess the comment about Carbon should be, “watch this or Vms’s space”.


    Sent from my iPhone using Tapatalk
     
  16. Wibble

    Wibble Fish don't talk
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    They'll end up sticking a carbon fibre print over the top!
     

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