(nearly) Hard earned lesson

[sea_ledford]

I think it was lack of loop circulation while I was alternately on and off the loop. Gas path would go from solenoid through the scrubber, into the counterlung, then back up past the cells. If the gas isn't being circulated, the solenoid will keep adding O2 since the cells never get a chance to read it, and you end up with a big slug of O2 in the loop.

-Chris

 

[lv2dive]

Have you thought any more about shutting off the ADV once you get to depth (instead of on ascent)? I started off diving on a Meg and never really used an ADV. When I started diving the SF2, I decided to try the ADV. I did a few dives with the ADV on for the majority of the dive and I used a LOT more dil (at least twice as much).

I decided to go back to shutting the ADV off when I get to depth. I also periodically check (physically) over a long dive to ensure it remains shut off (contact could push it to the "on" position). In addition to keeping up with my PPO2, obviously.

Thanks for sharing your story!!!

...ADV is open, I'll shut it off on ascent though. I don't think I'm unaware of when I'm bottoming out the CL (most of the time anyway), since I learned on the SM unit and it beat me up everytime I had other than ideal loop volume.

Certainly could have contributed though...

 

[StuartAcklam]

I think it was lack of loop circulation while I was alternately on and off the loop. Gas path would go from solenoid through the scrubber, into the counterlung, then back up past the cells. If the gas isn't being circulated, the solenoid will keep adding O2 since the cells never get a chance to read it, and you end up with a big slug of O2 in the loop.

-Chris

when leaving the Loop was it below your SP and did you switch to OC (new version: "Bail"? If "yes" the question is... does the SF2 keep adding O2 into the loop when your in bail mode... i am pretty sure it doesn't. BUT! I will test this to be certain. You can test this pretty easy. in the water and dry.

Stuart.

 

[joshk]

when leaving the Loop was it below your SP and did you switch to OC (new version: "Bail"? If "yes" the question is... does the SF2 keep adding O2 into the loop when your in bail mode... i am pretty sure it doesn't.

Switching to bailout triggers a low setpoint switch. It will add oxygen to maintain that low setpoint.

 

[sea_ledford]

when leaving the Loop was it below your SP and did you switch to OC (new version: "Bail"? If "yes" the question is... does the SF2 keep adding O2 into the loop when your in bail mode... i am pretty sure it doesn't. BUT! I will test this to be certain. You can test this pretty easy. in the water and dry.

Stuart.

While trying to address the issue, I didn't bail out on the computer. This whole thing took maybe a minute from recognizing the problem to deciding to fully bail out. Once that decision was made I did swap over to OC on the controller and my backup.

Last fall I did a complete bailout from depth drill, and was surprised to find out that the SF2 keeps adding O2, even though the controller is set to OC. I don't know if it automatically switches to low as joshk said, I didn't think to check. I fumbled around with trying to vent the loop as I ascended, but the reality is I'm still negative with a completely full loop (once my wing is dumped), so I just let it leak gas out the OPV on ascent and didn't worry about it.

-Chris

 

[sea_ledford]

Have you thought any more about shutting off the ADV once you get to depth (instead of on ascent)? I started off diving on a Meg and never really used an ADV. When I started diving the SF2, I decided to try the ADV. I did a few dives with the ADV on for the majority of the dive and I used a LOT more dil (at least twice as much).

I decided to go back to shutting the ADV off when I get to depth. I also periodically check (physically) over a long dive to ensure it remains shut off (contact could push it to the "on" position). In addition to keeping up with my PPO2, obviously.

Thanks for sharing your story!!!

I'll most certainly give it a try! I don't think I'm going through dill like crazy usually. My typical profiles are 150-170 for about an hour run time each, and I can get 3 dives out of a 3L cylinder before I need to top it off, so maybe 500-700 psi used per dive. One of the main issues with being the only CCR diver is I can't compare that sort of thing to someone else though.

 

[TotDoc]

(at 150) I notice my HUD is flashing red for cell 1. That’s no good. Check my hand set and cells are reading 1.67, 1.28 and 1.29. Solenoid isn’t going crazy, so I do a dill flush to confirm that cell 1 is the bad one. I really lay on the MAV, circulate the loop, nothing seems to be changing.

What dil were you running? Even if you were running air, your dil pO2 would only be about 1, so if you mashed on a dil flush with a rich pO2 in the loop, you aren't going to aggressively drop your pO2. If you had a few percent higher O2 in your dil, like the 23"ish" in your bailout, then you'd have an even harder time. Also, if you didn't turn off your O2, your solenoid will be adding O2 while you flush, as you already had 2 cells below the setpoint.

I realize that once I get a slug of air from my bailout I’m not going to be thinking clearly, but I’ve done the trimix to air swap at depth before so at least I know what I’m in for.

So SOME kind of trimix in your dil - but did you analyze this gas in the "back up" tanks? I always get suspicious when someone refers to the bailout as "23% maybe" that maybe you aren't being super vigilant about checking your mix

So I switched to OC on my BOV...I get back on the loop, flush again, now cell 1 is 1.3, and 2 and 3 are 1.6. I have probably floated up to about 130 at this point. ...Check my dill SPG and it is empty.

So you flush repetitively in anger, have no real success at driving down your pO2, so you bail out, but don't tell the computer you did so. Now you are ascending a bit, so the loop pO2 drops, the solenoid starts to fire to keep your 1.3 setpoint, but is unable to move the pO2 because you are not circulating the loop. When you get back on and flush, you circulate some gas around the loop, and your 2 cells that are presumably reading normally are reading high..and that would make sense.

Of course, you have been repeatedly flushing at depth with a 2L dil bottle, and now your dil is empty.

Still narked...

I am betting this had a little to do with what happened, too...obviously harder to focus on problem solving when this is a factor.

Overall, just really glad to hear you're OK!

 

[sea_ledford]

What dil were you running? Even if you were running air, your dil pO2 would only be about 1, so if you mashed on a dil flush with a rich pO2 in the loop, you aren't going to aggressively drop your pO2. If you had a few percent higher O2 in your dil, like the 23"ish" in your bailout, then you'd have an even harder time. Also, if you didn't turn off your O2, your solenoid will be adding O2 while you flush, as you already had 2 cells below the setpoint.

So SOME kind of trimix in your dil - but did you analyze this gas in the "back up" tanks? I always get suspicious when someone refers to the bailout as "23% maybe" that maybe you aren't being super vigilant about checking your mix

So you flush repetitively in anger, have no real success at driving down your pO2, so you bail out, but don't tell the computer you did so. Now you are ascending a bit, so the loop pO2 drops, the solenoid starts to fire to keep your 1.3 setpoint, but is unable to move the pO2 because you are not circulating the loop. When you get back on and flush, you circulate some gas around the loop, and your 2 cells that are presumably reading normally are reading high..and that would make sense.

Of course, you have been repeatedly flushing at depth with a 2L dil bottle, and now your dil is empty.

I am betting this had a little to do with what happened, too...obviously harder to focus on problem solving when this is a factor.

Overall, just really glad to hear you're OK!

Yep, pretty much nailed it! The CCR was working just fine aside from the condensation on the first cell, everything else was a problem of my own doing.

I'm totally anal about analyzing and marking all my gasses, I just couldn't remember for sure off the top of my head what my mix was when I wrote this up. Dil was 19/43, bailout was 23% and 98%.

And it looks like I might have found some helium (after searching for 3 months) so I can put some of that in my bailout too!

-Chris

 

[Long-John-Silver]

Do you leave the head opened capsized to let sensors dry at the end of the day?

 

[sea_ledford]

Do you leave the head opened capsized to let sensors dry at the end of the day?

I take the loop hoses off, but don't completely remove the head. On the SF2, there isn't a way to keep the sections together unless the head is attached. Also this is on a liveaboard so all the dive gear is outside and getting wet between sites, and it needs to be strapped down in case it gets rough. That is why I was laying it down in the first place.

On our last trip the valve on an 80 was destroyed when the tank and BC fell out of the rack and landed on the deck valve first. At least the 1st stage wasn't attached. Just flattened the top side of the threads.

I think I'm all of the second CCR ever on the boat, so I'm still working out procedures (obviously).

-Chris