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Wibbles Wonderings on Rebreathers

Discussion in 'Rebreathers Closed and Semi Closed Circuit' started by Wibble, Jan 16, 2016.

  1. Wibble

    Wibble Fish don't talk
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    For those of us not in the know, what's the difference (between an Inspiration Classic and an Inspiration Vision)?

    Also, whilst we're on the subject, what's it like to dive a rebreather?
     
  2. Doomanic

    Doomanic Dinosaur Wrangler
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    The basic construction is similar, the difference lies in the electronics.
    The Classic has a pair of Handsets (or paddles), each is capable of monitoring the PO2 and firing the solenoid that injects O2 to maintain the set point. One is the master, the other is the slave. The slave takes over if the master fails. The handsets control the set point only; there is no depth display and no dive computer function. They are also prone to cracking.
    The Vision has a single handset with 2 separate controllers in it. The handset is a significant advance over the Classic handsets with improved optics and deco management. The new 2020 handset is another leap forward, with a colour screen bringing the vision into the 21st century.
     
  3. Doomanic

    Doomanic Dinosaur Wrangler
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    [​IMG]

    It's quiet. All you can hear (hopefully) is the psssst of the solenoid injecting O2.
    It's a bit of a faff; there is, IMO, a lot to do before you get in the water and you can't just chuck it in the garage when you get home. For recreational diving it's a bit pointless, go deeper though and it makes much more sense.
    Buoyancy is different; you can't make small adjustments on lung volume as that's constant through the loop. It's not difficult though, at least so far...
    I'm currently using the suit for buoyancy, which I don't like, but it means one less expanding gas bag to manage on ascents. Hopefully, that will change as I gain experience.
    You need a lot of lead; I've currently got 11kg spread around the rig; 4kg in each belt pocket and 3kg in the trim pouch on the wing. That's probably a bit too much (I can hold a 1m stop easily) but most of it is down to the AP Floatmatic™ Harness. I'll be ditching that after MOD1 and fitting a SS BP and OPH.
     
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  4. Wibble

    Wibble Fish don't talk
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    Thanks for that, just what one 'rebreather curious' person needs to know.

    So you'll set the set-point as the partial oxygen pressure (PPO2) and the box will inject either Oxygen or Diluent (the other gas, possibly air, which has a lower PPO2) to control the PPO2 as you consume the Oxygen or change depth. I suppose the sensors they use in the classic return the ratio of Oxygen to other gas (Nitrogen, Helium) which is why the is no depth display.

    Which set points would you normally use during a dive?

    Does the classic have the flashing warning lights under your eye?
     
  5. furryman

    furryman hmmmm
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    Come to Buckland tomorrow and you can stroke my box...
     
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  6. Doomanic

    Doomanic Dinosaur Wrangler
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    Not quite; only O2 is injected as only O2 is depleted by the breathing cycle. Dil is only added as required by depth changes (deeper) either by a pressure activated demand valve (ADV) or using a Manual Add Valve (MAV).
    The Vision handset has a depth sensor in it, just like a normal dive computer. The Classic and Vision use the same sensors for measuring PO2, it is after all a function of depth.
    Dil is chosen to suit the dive, for dives up to 40m air is OK, but over 30m many use Trimix. Some use Trimix for all dives. 10/50 seems to be popular amongst some as it's easy to mix but is bloody stupid as it's not breathable on the surface. I'm probably going to use 18/45 or 21/35 as I will be using my Euros as a gas bank for the time being and it's a mix I can use OC if/when the YBOD beeps at me on a trip.
    0.7 when shallow, 1.3 when deep
    A Head Up Display (HUD)? No, and that's it's biggest failing in most people's opinion. The AV1 I want to buy has a HUD.
     
  7. clique

    clique Active Member

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    Hello hello,

    There's only a single solenoid which injects O2 when the control system detects that it is below your set point. If the PPO2 were to creep above the set point the control system will wait until it drops below it again before injecting more in.

    The classic has an alarm when the PPO2 reaches 1.6bar, from there you'd have to manually do a diluent flush to lower the PPO2 (which is one of the skills you learn on your mod 1) In essence you manually add diluent, while dumping the higher O2% mixture from the breathing loop (exhaling or using the dump valve on the counterlung).

    The sensors in the classic return a voltage (mV end of the spectrum) based on the PPO2 they're exposed to, when you calibrate the rebreather you are setting the mV signal to a known PPO2 - 100% at atmospheric pressure. I'd say one of the big departures from open circuit diving is having to think less about what O2% you have, because its changing with depth - and more about the PPO2 instead.

    Standard set points on the classic are 0.7 bar (Low Set Point) and 1.3 bar (High Set Point)

    The classic doesn't have any flashing lights - The Vision might come with a heads up display (HUD) as standard, I'm not sure! But I know you can get it as an upgrade. Almost all the visions I've seen have had them fitted.

    Hope this helps,

    Mike
     
  8. Wibble

    Wibble Fish don't talk
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    Interesting. A lot more to come to terms with than open circuit (OC).

    Daft question: what's it like to breathe? Is it harder to breathe than OC, and what's the 'dampness' like? Is it warmer, especially when the ambient temperature is low?

    I must "have a go" on one sometime:)
     
  9. Doomanic

    Doomanic Dinosaur Wrangler
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    Oh yes, it's not fit and forget, you have to monitor it constantly, after all the manual says;
    Again, it's different. On OC, you have to open the demand valve so there is a definite "start" to the inhale cycle. I haven't found that to be the case on CC, where the loop is at ambient pressure at all times.
    I'm not finding that to be the case so far, but it's early days.
     
  10. furryman

    furryman hmmmm
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    Regarding dampness: something I noticed on my first long CC dive was that I didn't come up gasping for a cuppa. I put that down to the fact that I was not losing so much water by continually hydrating the super-dry air from my OC cylinders.

    Regading warmth: it was still sodding cold in the lake today. (7 degrees by my comp)
     
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  11. Joe

    Joe Active Member

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    I only dive OC in the pool and its the noise that gets me
     
  12. barrygoss

    barrygoss Active Member

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    No noise on CCR. Doom even thought he could catch fish on CCR, they just don't care

    B
     
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  13. Dave Whitlow

    Dave Whitlow Well-Known Member

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    Yep, CCR is pleasingly quiet and you can hear the the sound of swimming bailout (OC divers) approaching in time to avoid them or hide if you wish. The other nice feature of CCR is you are recycling warm air rather than giving up your body heat by the lungful. This is especially obvious when you do a long dive with an OC buddy and they are shivering whilst you hadn't noticed the cold.

    Back to OP, to clarify the differences, as previous info was partially incorrect:

    Classic: eCCR with 2 independent set-point controllers each housed in a handset with the passive controller monitoring the active controller and ready to take over (as Dom said) and a buzzer to draw attention to the handset if something important is detected.

    Vision: eCCR with 2 independent set-point controllers located in the lid (with monitoring as per classic) and with a HUD showing status of the set-point controller(s), a handset showing output from each controller and incorporating a dive computer, and a buzzer to draw attention to the handset if something important is detected. If, once it is running, you severed the cable to the handset the Vision will behave like a Classic with a HUD.

    The 2020 handset is bright and coloured and has more RAM, uses bluetooth for PC comms, and has a compass (when software enables it) but otherwise is the same as the old handset. It is as clear underwater as the OSTC on my other arm

    The HUS is an additional output showing the same as the handset on a near eye display located on the breathing loop
     

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