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Wibble's CCR odyssey

Discussion in 'General Scuba Diving' started by Wibble, Jul 5, 2020.

  1. Dave Whitlow

    Dave Whitlow Super Moderator
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    If only I'd listened to your words of 'wisdom' when I chose to install a BOV! I'd have done exactly the same!

    It seems to me you are a person with more opinion than experience or wisdom and I advise people to ignore the shit you post.

    I've learnt a lot in over 10 years of CCR diving and little matches the shit posted on the subject by @Wibble
     
  2. Wibble

    Wibble Fish don't talk
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    Is there anything specifically incorrect in what I posted?
     
  3. Wibble

    Wibble Fish don't talk
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    Effect of shutting the O2 valve...

    Was doing more drills over the weekend targetting the response to the "3 H's" (hypoxia, hyperoxia, hypercapnia) -- thanks @Vanny

    The diluent flush on a Revo is through the mouthpiece as there's no dump in the lungs (excepting an over pressure valve). Inject diluent and use "leaky lips" to let the gas pass out of the mouthpiece. Injected gas (dil & O2) enters the exhale lung, crosses the scrubbers over the 5 cells into the inhale lung then exits through the mouthpiece. The O2 levels rapidly show a decline using this technique. Need to dump some gas from the wing to counteract the increase in lung volume.

    (A dil flush was run through on MOD1, but I hadn't re-run it since then. This will become part of the standard set of drills to run on every dive)

    Shutdowns. There's an issue with shutting down the O2 valve on a Revo which is the "leaky valve" will run down the first stage pressure leaving the first stage unpressurised and thus vulnerable to loostening and being unable to repressurise after turning back on. This is the same problem for all rebreathers with a stuck solenoid.

    I did turn the O2 off; I did depressurise the O2 system; it did erupt in a cloud of bubbles when turned back on. Thankfully, it re-connected after turning off and on twice more. It was impossible for me to reach the valve seal whilst wearing the unit. Solutions to this -- aside from bailing out -- would be to run the unit on diluent only (MOD1) or connect an off-board rich gas (MOD2).

    I concluded that in a bailout scenario the O2 should be left switched on to avoid the risk of depressurising the O2 first stage and leaving it vulnerable to flooding (and needing a service).
     
  4. barrygoss

    barrygoss Active Member

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    Air came out. Water went in before that. Salt or fresh cos it’s in the solenoid now.

    If air came out, it wasn’t sealed.

    B
     
  5. Wibble

    Wibble Fish don't talk
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    Thanks for that lovely news :)
     
  6. barrygoss

    barrygoss Active Member

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    See. Not learning or thinking.

    That was a basic understanding of physics.

    De Pressurise a stage underwater and what happens (that’s from your OC days) it’s a gob of water as it purges through.

    It’s not rocket surgery.

    B
     
  7. Dave Whitlow

    Dave Whitlow Super Moderator
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    This was mentioned in post #95.

    Water in the first stage too and moisture in the cylinder is a possibility.

    There are bonus points for solving this equation... water+oxygen+steel= ????
     
  8. Wibble

    Wibble Fish don't talk
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    Cylinder won't have water ingress as it wasn't empty.

    Regs are designed to cope with water ingress otherwise they'd be exceedingly unreliable. For example, standard rich decompression stages are kept off, although pressurised, but this can easily empty if the second stage is purged or any leaks.

    As for a rebreather, it'll be a small amount of water that will eventually dry out due to the passing gas. The residue and any sediment passing though the gubbins is the bigger challenge, especially in the microscopic leaky valve orifice. Have to say that one would expect that one of the core requirements of a rebreather is to cope with this.

    I frequently check that the orifice is running correctly during the build process: should take 15 seconds to drain from 150 to 100 bar. If longer, it's blocked. The 15 seconds was measured when the orifice was known to work. Still don't know the IP nor flow rate, just that it matches my quiescent metabolic rate (which I monitor when on the bottom phase of a dive -- the PPO2 would increase).


    Suit inflate cylinders are very prone to flooding as you don't monitor the pressure and especially on a small tin it's easy to empty the tin; do that at depth and water ingress is inevitable. Worse than that, they'll fail a suit inflate as it can't be shot blasted (according to a testing station that failed one of mine).
     
  9. jb2cool

    jb2cool Moderator
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    I know I can do 2 dives on a suit inflate bottle but if just a one dive day I’ll still fill after just one dive. It’s just part of my dive setup routine
     
  10. barrygoss

    barrygoss Active Member

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    Wrong.
    If water is in the system, the whole system is at the same pressure - 200bar. The only thing stopping the water entering the tank from the reg is orientation.

    Salt crystals in the solenoid and orifice. Salt crystals and high pressure O2.

    B
     
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  11. Wibble

    Wibble Fish don't talk
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    So why then is the SOP to feather valves, especially O2 valves? Could also question, god forbid, that the benefit of the A-clamp is the seal's kept under pressure when the gas is turned off.

    Do we see O2 fires caused underwater on rebreathers due to contaminate ingress? (Have seen photos of an Inspo that had been destroyed by an O2 fire; don't know the detail of this incident)
     
  12. barrygoss

    barrygoss Active Member

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    Because feathering is better than dead and the standard advice of having your kit serviced if you suspect water ingress during use can be maintained.

    O2 fires occur when? When turning on, not underwater. The heat is generated by the first movement of the gas into the lp system

    B
     
  13. Wibble

    Wibble Fish don't talk
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    Was thinking about a pollutant getting into the first stage from the water, then being ignited when it's re-pressurised. Does assume that the valve re-seals after turning off and on again.

    As an aside, the AP cylinders have a nice slow-start feature which one hopes mitigates adiabatic fires.
     
  14. barrygoss

    barrygoss Active Member

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    Like salt crystals? (Underwater it’s too soon for the crystals to have formed, but when the kits all dried out....
    https://en.m.wikipedia.org/wiki/Triboluminescence

    B
     
  15. Wibble

    Wibble Fish don't talk
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    You often get bioluminescence in the Thames Estuary and other places. At night you can sometimes see the glowing wake of the boat. Peeing over the side creates a light show; even peeing into the toilet bowl (raw water flush). Maybe it's an age thing.
     
  16. barrygoss

    barrygoss Active Member

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    Different physics but

    B
     
  17. JohnL

    JohnL Well-Known Member

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    For light relief, I'm still lurking - Wibble always has his own views, as for luminescent pee, I nearly wet myself!
     
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