O2 Flush

[JonG]

I have been struggling with the 6m o2 flush recently, I consistently get to around 1.5 but rarely anywhere near 1.6.

I have changed to a Predator recently, and cells were changed in October but flushes were fine on the GF.

That said I am only diving in a quarry at 350m at present, the Predator accounts for the altitude change, but the GF doesn't.

In addition obviously temps are low so there is s big difference between checking the cells at home for 0.21 and 0.98-1.00 in 21 degs and then checking at 6m in 5 degrees.

The other possibility is that I've lost the ability to flush properly!

[Paulo]

Try doing a complete neg pressure before adding the o2.

1.6 is hard to get and maintain. 1.5 @ 6m is 93.75% so not too bad.

If you want to spike the cells, drop a few cms.

Anything at all apart from o2 in the loop wont get you 1.6 @ 6m.

[JonG]

Just for clarity it's the 6m descent flush to cell check, not running up enough deco to merit high PPO2 on stops.

[gobfish1]

Old money and new money
Try 6.4 should have your cells at the right depth to hit
The 1.6.
Depth depth gauge on rist cells on your head your
3 foot of the make all ready. In old money . 20 foot is not 6m

Hence no feel er is clocking up 2.2 per minute CNS at 6m
Ps just do the test at 7m :)

[Dave1w]

Some people said they had no problem but on my Kiss I would struggle with O2 flushes getting past 1.5. It never really bothered me to be honest


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[jb2cool]

Could it even be that since the head is behind you that it’s shallower than your wrist mounted computer or is that bullshit?

[Paulo]

Could it even be that since the head is behind you that it’s shallower than your wrist mounted computer or is that bullshit?

If you can crack the code, that is what Gobber said as well

[Capt Morgan]

How do you stop the Dil entering, isolate the tank?

[jturner]

Just for clarity it's the 6m descent flush to cell check, not running up enough deco to merit high PPO2 on stops.

As others have said, assuming you can stop on the descent, check them at 7-8m or at maybe 5-6m when dropping fast (and you'll get a spike created for you). personally, I do the latter if I'm checking them before the dive, though typically I check them at the end or give them a quick spike at depth.

[JonG]

Thanks gents last night after posting it did occurr that 6m is not an absolute necessity, given that they have been checked at 0.21 and 0.98-1.0, I just need to know they will climb above set point to approaching the matching PPO2 so as others have said 6m is really too shallow taking into account differentials gauge drift etc.

Dave I do find the unit a pain to flush TBH, but its rare that a dil flush is required in fairness.

[Vanny]

To be honest I don’t do this until I reach bottom. A squirt or 2 of O2 sees the cells climb above set point so I know their not limited. A dil flush is easy enough on the AP but rarely needed after this. Stopping at 6 or so on most of the shot lines would be a hang on with 1 hand and work with the other , not great really. I aim to do this a couple of times during the dive , particularly around 20 mins in as the scrubber is up to full temperature and apparently that is when a cell may begin to exhibit issues , obviously could play up at any time.

[JonG]

I only do it on FW dives Vanny, like you I check at depth and then on ascent for next dive, but with time in the quarry I have just got into the habit of checking, plus wanted to know new(ish) cells and computer were all in line.

[Paulo]

I have been known to spike the cells on the bottom. Up to 2.0 for a second or 2 and back below 1.5 after 2 breaths. Lets me know they are working.

Other than as a skill on a course I cant say I have ever done it at 6m. Not sure I would want the o2 in as I was descending. I know it will drop with the DIL adds on descent but as Mike said, you end up clothes lining and in everyones way on the way down.

[nigel hewitt]

A nice warm humid scrubber contributes 0.05bar of H2O.
On most rebreathers getting 1.6 at 6m is a fault unless you are injecting straight into the head.

[JonG]

A nice warm humid scrubber contributes 0.05bar of H2O.
On most rebreathers getting 1.6 at 6m is a fault unless you are injecting straight into the head.

So does that mean that 1.55 on the handset would really be 1.60 or 1.50 Nigel.

[nigel hewitt]

So does that mean that 1.55 on the handset would really be 1.60 or 1.50 Nigel.
1.55 on the handset is just O2 plus a saturated level of H2O at an absolute pressure of 1.6bar
So that is, for example, a day when the air pressure happens to be 1000mbar and you are 5.94meters deep in 1030kgm/litre sea water.

So basically, yes but I can quibble the last digit forever.
It's 1030mbar on my barometer today so that's another 0.03Bar but does that effect your depth gauge too or are you using 6 meters of wire to the calibrated float to set the height of your rebreather and what part of the rebreather sets the gas pressure in the loop. Remember that water pressure changes cm by cm but air, within tolerances you can measure, doesn't?

[WFO]

I worried about this for a while, then decided that 1.5 or above would be right and anywhere over 1.6 would make me think I had a problem with a cell

[graham_hk]

...

[JonG]

Was probably/definitely over thinking stuff, too many changes in a small time frame, cells, computer and altitude and lost sight of what I was actually trying to achieve, namely checking for current limiting which beyond 6m isn't depth limited.

Many thanks for the replies though.