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Discussion in 'Rebreathers Closed and Semi Closed Circuit' started by Doomanic, Feb 28, 2016.
Do the BMCL sit above the wing? I guess there's an issue of them interfering with each other?
No. They sit between the backplate and the wing. I've got about 15mm of spacers between them to allow clearance for the lungs. Once I get rid of the horrible plastic box I should be able to reduce the spacers.
Of course, one's lungs can contain a litre or two, but the wing is, say, 20 litres. So I suppose the BMCL have about 3 or 4 litres capacity?
Don't ever be tempted to 'save' on cells. The consequences are not pleasant. After seeing something go awry a couple of years ago I have a policy of changing a cell every four months. That means I never dive a cell has been in the unit for more than a year and they are never 18 months old when replaced (I also have a spare which is used to replace the withdrawn cell). I also aim to avoid fitting cells from the same batch at the same time as they are more likely to fail together.
BMCL are wondrous when compared to the gigantic sacks of buoyancy I acquired when I bought my unit. You will not regret the change.
With BMCL, where are the manual add valves? Don't they typically plumb into the lungs?
With all this cell changing, what do you do with the old cells? And if it's "throw them in the bin", does anyone have one they can give me for my spare time "build your own o2 analyser" project that I've found instructions for on the internet?
They do, yes. I now have remote MAVs that come over the shoulders.
I will have eventually, but there's no point sending a cell that is known to be knackered.
define "knackered": if we are talking about normal current-limiting age, so long as a cell will read up to just over one bar, it should work for a O2 Analyser at 1atm. The issue arises when it becomes current-limited to the extent that it won't calibrate properly at 1atm, or if you want to use it at higher pressures. Most of us will have tins around the 21%/50%/100% mark, which should be enough to enable a three-point calibration.
@NickPicks : I have a couple of older cells knocking around still, one of which absolutely plummeted before Christmas, so probably won't work for you, but the other may well do. (and even the duff cell will probably work enough to tell you when he analyser doesnt work!)
I have a couple of old cells that I removed last year due to routine replacement, rather than failure, both are NaNS01 cells dated 2014-06. If you want to play with one then let me know where to post it.
On Saturday it calibrated at 1.14 in 98% and was current limited at 1.2. It was also very slow to settle after depth changes, throwing cell warnings left, right and centre.
I personally wouldn't trust it in isolation.
@Doomanic: Wouldn't be a contaminated/wet membrane would it? Wandering suggests that the O2 diffusion is not happening properly.
I agree though I wouldn't trust it for life support purposes.
@furryman: I don't know, but a new cell is going in before I dive next. Calibrating at 1.14 is enough for me, never mind the wandering.
A short update.
I've now done 4 dives with the back mounted lungs and whilst the clutter-free front is great and it's easier to control loop volume with the smaller lung volume, in the water I prefer the front mounted lungs at the moment. I know it's just a case of trimming the unit out, but I guess I hit it lucky with the FMCLs and it trimmed spot on first time so it's a little frustrating.
I dropped 1kg out of the top trim pocket for dive one but I was still head down unless I consciously fought it. Dive two was a little better (familiarity?) but I still wasn't happy so at the end of the dive I asked my buddy to remove another kilo from the trim pocket. With min loop I was able to hold a 1m stop so hopefully it will be a bit better next time.
Have you tried ankle weights?
Sounds like it is quite a transition from OC to CCR, I will bear this in mind if I take that plunge.
When, not if.
A short(er) update...
Another dive done today. The new cell is calibrating closely with the old cells, so that's good.
The unit is much better now it's down to 1kg in the top trim pocket and I found it much easier to hold flat trim.
It's gone 11kg of lead with the floatanium harness to 4kg with a 5mm backplate and it feels like there's more to come off. Once I get a stainless cage on it instead of the plastic box I think the rest of the lead will be consigned to the garage again. Or I can leave it on and use my Halo...