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Wibble's CCR odyssey

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

  1. Wibble

    Wibble Fish don't talk
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    Just passed a milestone of my first 50 hours of diving on a rebreather. So much more to finesse and learn.

    it’s been a lot of fun and has resulted in many changes of mind in the way that certain techniques and kit which are of moderate use when diving open circuit become very useful when diving CCR. For example big and sturdy reels which are a moderate convenience in OC become almost essential or the very least exceedingly useful when diving CCR.

    As Barry pointed out some time back, it’s the ascents which are the major challenge. They’re just so busy on CCR. The addition of a large reel massively simplifies decompression stops, effectively damping any small vertical changes.

    Enough about the skills, it’s the amazing flexibility that CCR brings to diving. The marginal gas costs are tiny compared with open circuit. This means that all dives can be helium dives and there’s much less focus on gas planning and optimisation — pick a standard gas and pretty much use it for all dives. Have settled on 18/45 for now and at around a fiver a dive it’s a no brainer. With the Revo consuming only 1.3kg of lime costing less than a fiver, again there’s no reason to eke out the scrubber.

    Diving is so much more pleasurable when diving CCR. Aside from the lack of bubbles roaring past one’s ears, no bubbles means the fauna isn’t disturbed, so fish swim around you, not away from you. When inside wrecks there’s no bubbles to disturb the space above you, so no rust snowstorm. There’s also little gas stress leaving one the time to get on with the dive, if you get stuck or lost, just chill — don’t worry, be happy.

    The rebreather demands respect though. You can’t skimp on preparation which means allowing for an hour of preparation the night before. When diving it needs constant monitoring. I’ve settled on mainly running it manually with the computer as backup — manually changing setpoints, manually injecting oxygen and diluent as required to maintain the desired setpoint, I.e. keep the machine set to 1.2 and run it at 1.3 or 1.4 as required, and running the deco a little higher if it’s not too long.

    Sidemounting the bailout and deco stages keeps them well under control. Out of the way and not swinging around to catch on a wreck. Generally dive with two stages to minimise bailout worries.

    Really not regretting my selection of the Revo. Love the engineering, simplicity and redundancy. Two scrubbers, who’d have thought it! The Nerd is an amazing tool, can’t recommend highly enough. Five cells... removes cell angst, fine by me.

    So much more to finesse. Can work on the during the next 50 hours! Will be taking it underground when the sea's off limits.


    Utterly delighted with the past three months of intensive diving in such a strange year. Looking forward to many more.

    Many thanks to all people on here who’ve helped me on this journey.
     
    JimmE, Harvey-NG, jps and 3 others like this.
  2. Wibble

    Wibble Fish don't talk
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    Small update on the sidemounted stages. The sidemount configuration works exceedingly well, keeping the cylinders out of harms way whilst allowing fast and easy access to the bailout.

    The stages have a standard "handle" mounting with two large bolt snaps. The pipe (handle) is rotated 45 degrees around the cylinder to facilitate clipping on the bungee.

    Sidemounted bailout 3.jpg
    Sidemounted bailout 1.jpg

    As mentioned previously, the harness has two chest D-rings each side. The lower one is used for clipping off the stages (and the backup torch) and will be pulled flat when the bungee's attached, which obviously makes it difficult to use the D-ring for clipping off the myriad other crap to your chest. Thus the top D-rings are used for that (with the bolt snaps shown below). Also shown below is the "get me out of my harness" loop, making me more self-sufficient de-kitting on the boat.

    Revo harness 4.jpg


    The stages have both clips used, so they're basically bog-standard stages although using LH & RH modular valves, so can be handed off to any other diver if necessary. The top clip is clipped to the lower chest D-ring and remains in place. It's possible to undo this before attaching the bungee for that full sidemount experience, but it's not necessary on my config. The lower stage clip is attached to a "Billy" D-ring on my waistbelt (can be seen on the top picture).

    From the pictures above, you can see the LH cylinder (ali7 232 bar) has both clips pulled back by the tension of the bungee. The bound/whipped piece of bungee is a simple handle: grab it and pull it off the modular valve (this is a lot easier than a tight loop which you end up tearing your dry gloves).

    I know that there's some slight tweaking to be done with the position of the waist D-ring, but that's all the pleasure of farting around with sidemount, the seemingly never-ending tweaking to get the kit "just so". But once done, it's ninja every time!
     
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  3. Wibble

    Wibble Fish don't talk
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    Been several months since last posting here.

    Am really enjoying diving CCR even with all the additional faff it entails -- allowing plenty of time to clean and prep the unit prior to diving. Have now passed the 100 hour milestone with 80-odd dives on the unit. Still not an expert, but very much happier diving on the unit. Buoyancy's arrived so decompression hangs aren't a problem now and have reverted to leaving the reel a metre or so below me and the string going through a double-ender held in the hand (so it doesn't cut through the drygloves).

    MOD2 was a great experience, very different to MOD1. In essence it was talking things through and learning more nuanced issues of planning, running the unit, in-water resolutions, etc. Whilst it's more team oriented, MOD2 is still self-sufficient but there's very much a limit to the bailout reserves.

    MOD2 was booked as a pre-requisite to a Malin trip in July; which was cancelled due to Irish covid quarantine requirements. Have something to look forwards to in 2022.

    Am using a second cloth in the exhale lung now. Water tolerance in the loop is Revo's weakness especially if you dive very flat as any water in the exhale lung tips back into the loop. This can even be from failing to 'squeeze' the loop dry. The second cloth, tightly rolled and tucked on the LHS, absorbs loose water and makes a massive difference even with condensate. The loop now doesn't gurgle after a longer dive.

    Aside from that, have kept the unit the same; no need for more modifications as it's as I want it. The bungees work very well with both 7s and ali80s. The harness is great. The AI transmitters work well with the Nerd.

    Christmas saw the delivery of a lovely Blacktip scooter. Been enjoying using that on various dives including a trip up to Kinlockbervie (Cape Wrath) where it was great fun hooning around in the kelp and crinkly bits. Found scooter diving's pretty straightforward after a few dives and mostly common sense.

    Only failure on the Revo was an RMS sensor (a.k.a. temp stick) in the scrubber which was intermittent. Couple of hundred quid for a new one, but sorted. The Revo's been great thus far. Changing a cell every 6 months seems fine. Having 5 cells takes away cell anxiety.


    Work's beginning to get in the way of diving. Need more holidays!


    Thanks for all your advice.
     
    jps likes this.
  4. splinter

    splinter Active Member

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    Does this mean you'll be using cells up to 30 months old? As I understand it the recommendation is not to use them past 18 months.

    I've been taught to change one every 4-6months or all of them after 12-18months (3 cells). Either way the cells aren't used past 18 months. I like the idea of one every 4 months personally. Means they're not all from the same batch and spreads the cost over the year.

    Glad you're enjoying it. Looking forward to getting my first 100 hours in.


    Sent from my SM-T580 using Tapatalk
     
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  5. Wibble

    Wibble Fish don't talk
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    That's the beauty of having 5 cells. With 3 you have to pre-emptively change them. With 5 you can see if one's failing and run them for longer.

    From the Revo checklist: is the youngest cell more than 6 months old? If so change out the oldest (or weakest) cell. Obviously if one fails, you swap it out then. I always have one "in stock" and seal old working cells just in case.

    http://www.revo-rebreathers.com/revo-downloads/
    http://www.revo-rebreathers.com/wp-content/uploads/2016/02/Understanding_oxygen_sensors.pdf
    http://www.revo-rebreathers.com/wp-...ygen-Sensors-part-II_the-complete-picture.pdf
     
    #165 Wibble, Aug 13, 2021
    Last edited: Aug 13, 2021
    jps and splinter like this.
  6. Doomanic

    Doomanic Dinosaur Wrangler
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    You're a braver man than me...

    Not that any of my cells lasted longer than 12 months anyway.
     
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  7. Dave Whitlow

    Dave Whitlow Super Moderator
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  8. nickb

    nickb Well-Known Member

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    When you read Raymakers' paper on this it all sounds very practical and even makes sort of sense.

    But, that's from the comfort of your armchair.

    At depth and whilst the shit is hitting the fan and the PO2 readings are all over the shop, trying to remember which of the 5 cells were last replaced and which were over two years old is not something I'd want to be doing. So, I can see no benefit from keeping cells in my unit once they've essentially expired. I put them in an O2 analyser after that and use them that way.

    This is very different to the 4th cell approach, where ALL of the cells are meant to be within spec.
     
  9. Dave Whitlow

    Dave Whitlow Super Moderator
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    That is bonkers!

    As the Raymaekers paper describes, oxygen sensors are made in batches and include an amount of 'fuel'. As they age, and the 'fuel' is consumed, their ability to read high is reduced. The damp, mixed gas, and high temperature environment within a rebreather scrubber is not a good place for the cell components and they can fail for other reasons. Warranty is for 12 months and the accepted wisdom is to replace any cell older that 18 months. With this in mind, having extra cells means you should be spending more on cells and not running them longer.

    The oxygen sensor is the most critical component of a rebreather and any sensor that can't be trusted is a liability. They are essentially reliable but must be treated with suspicion. They will eventually fail and the consequences of their failure can lead to poor decisions and grim outcomes. I have seen this first hand and it is not pretty!

    I have 4 cells in my unit and cells #1 to #3 are linked to the set-point controllers and cells #2, #3, and #4 are connected to my OSTC cR to provide independent monitoring in case of catastrophic electronics or handset failure.

    After listening to John Lamb at Eurotek, and reading his books and the Raymaekers paper, my general rules are:
    - only change one cell at a time
    - keep an unused cell sealed in the bag
    - avoid installing cells from the same batch together
    - cells #1 to #3 never more than 12 months old
    - no cell over 18 months old goes diving
    - at the end of dives push the cells above 1.6 bar ppo2
    - cell #4 will always be the oldest
    - if cell #4 failed ignore it until I get home
    - if #1, #2 or #3 fail disconnect it and use #4 instead

    If in doubt there's always another day to dive and you only die once!
     
    jps likes this.
  10. Wibble

    Wibble Fish don't talk
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    When a cell's misbehaving, it gets switched out from a sealed cell kept "in stock".

    Aside from that, I stick to the Revo's process of one every 6 months.

    In reality it means that cells are replaced more frequently -- think I've replaced 4 this past year, only one of the originals left. Each cell is marked with the month/year it's replaced.
     
  11. Doomanic

    Doomanic Dinosaur Wrangler
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    I just wrapped the receipt round mine; saved time when they failed...
     
  12. Dave Whitlow

    Dave Whitlow Super Moderator
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    Back in 2013 cells were unreliable whilst suppliers recovered from the Teledyne market exit but for quite a few years cells have been reliable with just the occasional failures, or batches with a higher return rate.
    Which cells were you using that we so bad?
     
  13. Dave Whitlow

    Dave Whitlow Super Moderator
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    yeah, you've been diving CCR for ages now so clearly an expert on cell reliability!
     
  14. Doomanic

    Doomanic Dinosaur Wrangler
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    I had two Narked cells fail and one AP16.
     
  15. Dave Whitlow

    Dave Whitlow Super Moderator
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    I had lots of APD14 failures in 2013 (including one underwater in low viz in March) and switched to NANS01. Once AP sorted the process APD14s have been reliable and that's all I've used.

    BTW Nans01 and AP16 are the same cell (made by Vandagraph)

    Why not use the reliable one from the manufacturer?
     
  16. Doomanic

    Doomanic Dinosaur Wrangler
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    Not sure I understand the question.

    I used the cells that were in stock so I could go diving.
     
  17. Dave Whitlow

    Dave Whitlow Super Moderator
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    I had cells, I had spare cells, and I bought cells that were is stock. I went diving and never missed a dive due to cells. We clearly did something different.

    I have a spare cell now,in addition to the 4 in the unit (one of which is due to be changed). I am about to order a new cell so I can retire the oldest (currently reliable) cell.

    I aim to avoid equipment interfering with dive plans.
     
  18. Doomanic

    Doomanic Dinosaur Wrangler
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    I bought a unit that needed cells. I knew that APD16 and Narked were the same so I bought 2 Narked and one APD. This was for two reasons; the main reason was in an attempt to buy from different batches, the second was because Narked only had 2 cells in stock when I ordered. AP didn’t have any 14s at the time. I later bought another AP cell so I had a spare. All three of the original cells failed at less than 12 months from date of purchase. One of the warranty replacement Narked cells failed very quickly too.

    Fortunately none of the cells failed on a sea dive. Not that I got many of those in.
     
  19. Wibble

    Wibble Fish don't talk
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    Not at all.

    However, I'm not expecting all five -- or two, three -- to fail at the same time. For once I'm following the manufacturer's recommendations and my training.
     
  20. barrygoss

    barrygoss Active Member

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    Mod 1 course for fun, inspo, buddy had two cells fail, one cell read 1.8, two read 1.2 and the O2 was pumping in. Then it alarmed then it stopped. I blew the bag and the buddy went up quick.
    Now you have three cells in the Revo that are new (under 18 months) one that is mid term and one that isn’t the weakest. (By the way some cells fail by burning out high, just like some candles flare at the end)

    I guess you’re doing a dil flush to work out which ones are the twats. Just like the 3 cell people.

    Even the Revo paper states it’s all a numbers game.

    B
     
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