Rebreather or not?

[Peter69_56]

Ok so how have I gone with my CCR experience? Well I sure have had an interesting time (read a number off issues). In the main due to a previously poorly maintained CCR unit combined with inexperience due to just starting to use it.

Issues
During the course I had multiple electronic faults, to the point where I ended up replacing every bit of electronics.
An inflator failure at depth which shot me from 30m to 0 in about 40 seconds while I tried to work out if it was my dry suit or wing.
Loss of CCR solenoid power at depth, so went to manual control (so glad my training kicked in).
Caustic hit at depth (even more so glad my training kicked in, and so glad I was carrying the correct gas volumes for total bailout at depth).

So now have MOD 1 & 2 done and looking forward to Mod 3.

What have I changed on my unit;
Replaced all electronics
Serviced the Predator controller
Replaced all the thermocouples
Replaced the REVO Dream with a NERD2 (and love it)
I am currently fitting a Bail Out Valve mouthpiece as (as posted previously by others), often its hard to get onto the bail out gas if things go very pear shaped.
Put a light weight stand onto it so its much more stable
Fitting soft bands for tanks
Fitted spacers to increase loop volume as I was always hitting no gas/excess gas in loop due to it being a micro unit with me having big lung volume.

I am anal about O2 sensors and testing maxing out the PPO2 at depth to prove operation, and also about how to pack canisters properly with sorb to prevent channeling. Also made a decision if I am not happy with something on the unit, fix it, dont try and struggle on until a convenient moment, its not OC, sort it or it could sort you out permanently.

My bouyancy control still sucks compared to OC but I am getting better, in particular when I have a dry suit on. As someone stated earlier, learn OC go to CCR then relearn CCR.

I hated my CCR for about the first 20 dives, but now I appreciate very much how much time you can have with an emergency to sort through the issue, in comparison to OC where if you lose air its DO SOMETHING NOW. Also I love the options you have with extending the time if things go very bad indeed, like being stuck in a wreck. OC you have maybe an hour and its all over, or you are badly bent in the rush to the surface with no gas, with CCR I can have maybe on a good day 7 hrs before I become a encrustation. As my instructor said, you have a lot more time, usually, however problems can be much more subtle, so remain vigilant, other wise you might not see the warning signs. If in doubt, bail out.

CCR Trimix diving is so cheap I now am currently running 16/45 on all dives at about $20/dive AUD for all consumables. All in all, very happy even if it has been a bit of a money pit. Bought it cheap, cost a bit to get it to a safe level of operation but in the end I now have a unit with all the goodies for the cost of a standard good second hand CCR unit.

 

[Gareth J]

Garath,

Also there is the mushroom valves in the mouthpiece (2 off one each side to ensure the flow through the mouthpiece to ensure one way flow) that can fail and cause a CO2 hit. When I bought my breather, I found that both the mushroom valves were totally RS and had to be replaced. How the previous owner used them without killing himself I fail to understand, as all that would have happened in use was that the gas would have just flowed in and out the same lung, without any path through the Sorb, and thus immediate build up of CO2 with no mechanism to remove it.

I think I mentioned one way valves in the first paragraph!

I'm glad you are enjoying your rebreather experience.

 

[Peter69_56]

I think I mentioned one way valves in the first paragraph!

I'm glad you are enjoying your rebreather experience.

I stand corrected, must have missed it first time. Thats what happens when you read stuff at 3 am while at work

 

[telemonster]

Old thread but noticed the first post said that CCRs are illegal in Saudi Arabia. Interesting, quick google didn't shed any light on that.

 

[InTheDrink]

Everyone that’s posted on here has more experience than me.

You sound meticulous and a good candidate for CCR altho the 100m goal seems a little arbitrary and contrary to using the right tool for the right job.

I narrowly missed death on CCR after a few hundred dives. And then realized l like shallow dwelling sharks and pretty fishies. So a CCR was pointless for me and I don’t have the right temperament for it. It does involve a lot more task loading and looking a your gear rather than what’s in the water. If you want to stay alive that is.

Good advice on here. I think the best advice has been a good few try dives and then think and also see what an instructor says/observes. My first CCR one asked me if I was ready to risk my life as he wasn’t sure I was right. I persevered, passed, crosses to another unit and came pretty close to dying. I wasn’t ready. I’ve the bones of a thousand dives now and I’m still not ready. CCR is awesome. But forgiving it is not.

Enjoy your adventures

 

[JacquesM]

The AP units CAN have CO2 sensors, these are a plug and go accessory (they are a consumable, like lime and O2 sensors). I am aware that there where early issues with reliability - i.e false positives. Again, having been through the learning curve they are a lot more reliable.

Hello
I am an AP diver and owner, did think a good bit around these sensors, and did not buy them.
Why not use it as it is available ?

Because AP units already have a terific tool built in, sold as an option but part of any unit that I saw till now. That is their Temp Stick, a patented tool that measures temperature in various parts of the scrubber and shows,from it, the effectiveness of the soda lime in real time.
Yes : unused lime is cold, the captation of CO2 is exothermic, so the active part becomes hotter, and you see it. Then the lower (starting) part is exhausted, is cools down and is displayed as inactive.
So you can see that your scrubber works, that it becomes older, that it will soon be overused ... Oh no, you shall never wait till that moment, at least duringa dive. When a good ^part of it was used, you did throw away the mixture and repacked a fresh one.

On the opposit, what would detect a CO2 detector ? That it is too late, scrubber was overloaded, CO2 is there, you should already have ascended, please jump to OC, ascend, and pray to succeed quickly enough.

Make your choice, get advice in advance, or alert at the last minute ? And one who knows he will get Alert could easily rely on it, just for one more dive ...

 

[JacquesM]

From your post, you don't understand the operation of a CCR unit. To explain it i a post is not ideal but I will try to give you a simplified overview.

That was nice reading.
One important point to add : point is not only on the unit, it also is on the diver.
Remember your old OC lessons, why and how you could face troubles with CO2 : not enough exhalation.

An important difference between OC an CC is that in CC the only engine that runs the loop and moves the gazes, allowing CO2 absorbtion, O2 measure and mix, is the diver's lung.

No help here from the input pressure, and these marvelous venturi help and other tricky pieces in the OC reg 2nd stage. So in order to run the unit, you need to push the loop content.
When tired, because you made an effort, you have more CO2 to eject and less natural tendency to do it. The more you need it, the less ease is there. And that makes it very difficult to overcome the beginning of breath shortness

Of course this also worthen the troubles brought by the hardware, if any.