JJ CCR newbie questions

[kensuf]

Every CCR has negatives, the biggest nits IMO on the JJ are the lack of flood tolerance

Can you elaborate on this? I was under the impression you could dewater the unit, but in the event of a flood there will always be a little bit of water in the CL's.

 

[doctormike]

I actually thought that the flood tolerance was pretty good, but then again I don't have experience on any other units...

 

[rjack321]

Can you elaborate on this? I was under the impression you could dewater the unit, but in the event of a flood there will always be a little bit of water in the CL's.

I haven't dove one, but from a buddy who does... So with some salt here. My understanding was that its pretty difficult to get water to the counterlung dump and not also have it get to the scrubber. Small floods being clearable (unlike in a revo which is basically impossible to get any water out of) Bigger floods are going to end up in the scrubber just because of the backmounted lungs and T pieces. Compared to say a HH or a Meg with OTSCLs where you can basically continually clear from (e.g.) a torn mouthpiece.

 

[doctormike]

I was able to clear an (admittedly limited) flood by going slightly head up, accordianing the exhale loop, and doing a barrel roll (either partial or complete) to the right (exhale) side. That puts the CL drain in a dependent position, and a forceful exhale pushes water out from the bottom. Again, I have nothing to compare it to - I have done test flights on a revo, an Inspiration and an Optima, but never to the point of a flood drill.

 

[rjack321]

Thanks so much! This is pretty much what my instructor had recommended as well...

There's a certain number/population of divers out there who believe the eCCR is continually trying to kill you and running the unit manually on a low SP is the way to mitigate that.

The rest of us (my included) accept that absent a failure the eCCR is trying to keep me alive. Adding diluent when the volume is low or adding O2 as its metabolized. Instead of me continually diving it like its going to kill me every minute of every dive I prefer to spend my mental bandwidth looking for anomalies. The big ones being CO2, are all 3 cells telling me the same basic thing and at the correct level, and is the solenoid firing periodically.

Some people swear by running them manually, leaving the so at 0.7. This forces you to pay attention to the ppo2. For me, I think the biggest risk is failing to pay attention and missing a failure which results in low ppo2, but I prefer to try to pay attention than to run manually the whole time. I tend to intervene more for accents as I know what is happening next so have an advantage over the computer.

In my class I had mine set at 1.2 but was supposed to be running it at 1.3. What a horrendous PITA for a brand new CCR diver. Now if I decide to run a manual dive just for practice I set it at 1.0 or 1.1 and run it at 1.3, much less annoying. I don't think I'd use the 0.7 setting, I really only use that at the start of a dive prebreathing and descent and then again once I have finished my 20ft stop (if any) and I don't want it dumping O2 into the loop on the surface.

 

[sea_ledford]

@sea_ledford, unless you're diving super deep with less than 100% O2, I'm not sure how your loop would be incapable of reaching a .7 setpoint, why wouldn't you be able to hit 1.0 at sea level? Realistically you may never be able to truly reach an FO2 of 100% due to other inert gas in the loop, but it shouldn't be enough that it would be pissing O2 out all over the place in an effort to reach 70% in the loop. Do you leave it at maximum loop volume at .19? I guess I never leave anything on my rebreather open to the environment once I pre-dive it, so it never crossed my mind that it would be anything other than low setpoint at a minimum. Once pos and neg are done, a setpoint check is done and it stays in that state until the dive starts. Making sure it maintains a stable setpoint should be part of your pre-dive anyway. What scenario would you do your predive and then leave the loop open? Hitting 1.6 for a 6m cell check is gonna be a bigger waste coming from .19 than .7. I guess I just don't understand why you'd have your loop at anything other than low setpoint or higher once you've predived the unit. I'm not saying it's incorrect, I just haven't seen a scenario in my rebreather diving where it would ever arise.

I'm thinking post dive, not pre-dive. Actually between dives is when the problem would happen. Do a dive in the morning, have plenty of scrubber and gas left for another diver after an couple hour surface interval, but take off a hose or open the BOV to get let things dry out a bit between dives. Cells will be less than .7 since it is open to ambient air, and if the computer gets reactivated it'll start adding O2, which won't ever get circulated to the cells (I guess this is dependent on the specific CCR, but on the SF2 the cells are downstream of the BOV) so a .7 pO2 would never be reached. Or you could breath down the pO2 of the gas a bit while getting out of the water and just shut off the computer rather than bring the gas back up to above .7 before climbing out of your gear, not thinking that someone will drip all over your rig and fire up your computer.

I'll usually do a dil flush/ circulate some gas around using the counterlung to try to knock the humidity level down between dives, so all it would take for my specific unit would be reactivating the computer, so I use .19 all the time on the surface.

-Chris

 

[Wayne at DiveSeekers]

i have familiarity with multiple RB's, and have been diving the JJ non stop for the past couple of years. The JJ has been nothing but easy to use & reliable. I use it for all (teaching/fun dives) of my diving. It is specifically designed as an eccr and holds set point amazingly well. I use to come from the mindset of flying manually and if you have a computer use it as a parachute, but the JJ has changed that. As a RB diver you are always in tune with PO2, if not you shouldn't be diving a RB. This doesn't change with the computer. All that being said, I practice what I preach to my students and practice the skill of flying manually. Shearwater electronics are great, rock solid and you can't beat the customer service. Flood tolorance on the unit us great. Back/side mounted 4l counter lung with t-piece that is equipped with a built in baffle and OPV on the bottom of the lung. Besides the counter lung, the scrubber sits several inches above the bottom of the canister housing, so you still have some room there. You have to do something majorly wrong to flood this unit.

 

[kwinter]

You have to do something majorly wrong to flood this unit.

Been there, done that. But Wayne knows I can screw up anything if I try hard enough.

I started years ago with eCCR on an Optima. I yearned for a hCCR and leaky valve. Eventually I got a rEvo, and learned that I hated the leaky valve. It's just because I didn't grow up with it. Pop to the surface for a short bit and then descend again. But wait! Your O2 has been running the whole time. Not only do you have excess volume, but it is hyperoxic. Worse yet is that this same thing happens at depth if you bail off the loop for a while, whether by BOV or second stage. If you don't remember to turn off your O2 supply, your loop will keep being fed O2. So check the pO2 before you switch back. And then you have to remember to turn the O2 back on.

I found the leaky valve and hCCR to be a bit of a pain. I went back to pure eCCR with a JJ and another Optima. It's what I was raised on and what I'm comfortable with.

 

[Peter69_56]

I am looking at one as well.
My amount knowledge of how a CCR works you could fit on the end of a pin, as all my experience to date is OC to Trimix.
Are they good to 100m, and if so do they need any accessories to get them there or are they good right out of the box (as I want something that will allow me that deep with experience and time).
Any other info would be good

 

[KenGordon]

I am looking at one as well.
My amount knowledge of how a CCR works you could fit on the end of a pin, as all my experience to date is OC to Trimix.
Are they good to 100m, and if so do they need any accessories to get them there or are they good right out of the box (as I want something that will allow me that deep with experience and time).
Any other info would be good

This claims it was unmodified to 290m. I am guessing that would do.

UK diver claims CCR depth record

Actuall I think there will be people diving all the current mainstream ccrs to 100. The key thing is to get to play with some and see what you like. Read the manuals, read books and maybe take a course before buying.