Important features when choosing a rebreather

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LFMarm

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I am new to rebreathers and I am trying to figure out which features to have so that I can shortlist models that would be suited for me. From my research, I landed on 3 features that not all units have that would make diving easier and safer
  • ADV – Auto Diluent Valve (with or without a Flowstop isolator) — to automatically inflate counterlung when going deeper
  • Scrubber Life Monitor — the scrubber is the bottleneck for dive duration and hence great to monitor it
  • CO2 Sensor — Important for safety
Anybody would agree with these 3 being important features? Which models would fit the bill?
 
CO2 sensors are supposed to be unreliable and unnecessary; by the time they trigger it's too late.

You could also add a CMF - constant mass flow - or leaky valve. This gets into the manual vs. full automatic debate.

All of this is highly personal and gets into Zen and the Art of Motorcycle Maintenance.
 
I don’t believe there is a usable CO2 sensor for rebreathers made by anyone. It’s a hard problem.
 
My decision to go for a Revo was based upon:
  • Multiple scrubbers
    • CO2 hits would be way more unlikely
    • Cheaper to run as only one scrubber's replaced with normal diving
  • Fully redundant electronics
    • Two completely separate systems for monitoring PPO2
    • Separate sets of cells -- very happy with 3 cells on the controller and 2 cells on the backup
  • Nerd + Petrel
    • Has to be Shearwater; no other computers are acceptable
    • Extremely happy to have the Nerd as a head-up display
    • Fantastic when in compass mode
  • Fully enclosed lungs, no T-pieces, no external moving parts (loop aside)
  • Reliable system
  • Single mounting case to attach everything
    • Suit inflate, second O2, suit heater battery, second torch battery
  • Based upon a manual system, but with automatic "parachute"
    • CMF 'leaky valve' to reduce solenoid activity
    • I want to run it manually so I know what's going on
    • I don't want to run it automatically as I want to know what's going on
  • Simple, clean, clear controls
  • Scrubber monitoring system
    • As there's two scrubbers, I know when the first one's exhausted (never happened yet!)
  • Must be able to dive flat in trim (some boxes seem to require a head-up trim)
  • Must not have a reputation for problems; must have keen proponents
Am very happy with that decision.
 
I am looking for a rebreather too. Would like to add:
1. Amount of electronics; do you want to keep it simple or go all the way?
2. Weight; light config or heavy config (bigger cilinders on unit, less need for bailout cilinders)?
3. WOB; easier breathing is always nice.
4. Back mount or sidemount; I would opt for backmount.
5. Maintenance; how easy is it to clean and maintain?
6. Weight; can your back handle the dive ready weight including bailout or do you want to go lighter?
7. Computer interface; Shearwater or proprietary?
8. NERD/ADR/etc.; do you want a HUD or a whole computer with all information near your eyes?
9. ECCR/MCCR; both have their advantages and disadvantages.

I don't care much for scrubber life measurement and CO2. Scrubber time is mostly theoretical and easy administrated on a piece of paper. CO2 measurement sounds better than it is in reality.

For me, I still undecided between JJ-CCR and Divesoft Liberty. I like the Liberty because of the possibility to go sidemount later on, but I'am not sure I want that amount of proprietary electronics. JJ-CCR is simple, flexible and rugged and my primary choice for now. Still deliberating.
 
AJ:
I don't care much for scrubber life measurement and CO2. Scrubber time is mostly theoretical and easy administrated on a piece of paper.

Warning... Classic Revo diver response...

Some rebreathers work really well and can measure the scrubber quite accurately. With two scrubbers, the Revo can accurately determine when the reaction front has progressed into the second scrubber.

What's most important is that it shows you that there is a reaction front and you can watch that time drop if stressed, and as the dive proceeds.
 
I am new to rebreathers and I am trying to figure out which features to have so that I can shortlist models that would be suited for me. From my research, I landed on 3 features that not all units have that would make diving easier and safer
  • ADV – Auto Diluent Valve (with or without a Flowstop isolator) — to automatically inflate counterlung when going deeper
As a new CCR diver, an ADV will be helpful. After you have gained experience it will be less helpful. You have not given any of the reasons or type of diving you want to use the CCR for, that would be helpful. With experience a lot of CCR divers will adjust gas ahead of the ADV and find that the ADV adds gas when they don't want it. Yes, you can add a shut off to keep that from happening. When ADV's first came out I thought they would be great and got one, after time I found them more annoying than helpful and didn't use it.

Scrubber Life Monitor — the scrubber is the bottleneck for dive duration and hence great to monitor it

So far I have not had experience with a sorb monitor that is accurate enough to put a lot of faith in one. Again, as experience is gained, you will learn to gauge the life of your scrubber.

CO2 Sensor — Important for safety

There was a time when a CO2 monitor was considered the holy grail of CCR diving. The reality is that there is too much variance in human metabology for a CO2 monitor to give an accurate and meaningful alarm.

IMHO, what should be considered is configuration such as BM, SM, etc.
Over the shoulder counter lungs (CL's), BM CL's, etc.
ECCR, MCCR, Hybrid, etc.
The list of choices goes on and the wants and needs will be easier to narrow down knowing what type of diving it will be used for and the reason for going to CCR.
 
So far I have not had experience with a sorb monitor that is accurate enough to put a lot of faith in one. Again, as experience is gained, you will learn to gauge the life of your scrubber.

Have you tried the Revo RMS?


Definitely think the first rebreather should be a standard and common one as is possible so you can get the first few hundred hours well sorted in different conditions. There's plenty that meet this criteria which you'll be able to get good support and plenty of people to help you.

My first rebreather was this time last year: a Revo. Have now racked up 100 hours on the unit and am very happy, especially since MOD2 has enabled the diving which rebreathers excel at. But I know I'm just a novice and definitely need another one or two hundred hours more to refine everything. Am certain that had I have gone for the second choice, JJ, I'd be just as happy.

More diving, what's not to like!
 
I have been on a rEvo for ~8 years. It was my second rebreather. Not going to bash my 1st one, it has improved over the years and I am sure is great unit as well.

I upgraded from a pre-RMS rEVO to the RMS version when it in 2015. Overall a great unit. My only comment is the ADV is not that great. Sometimes it works way to well - others not at all. I have never been successful at getting it completely tuned correctly. My wife dives a rEvo as well and has the same issues with the ADV. We have just learned to accept it. That is not a show stopper on the unit and I would recommend it to anyone that is interested.

I am very glad we dove rEvo pre-RMS scrubber sensor. The scrubber monitor is great - but it is nice to also know the timing of scrubber canister rotation without it. Gives you a fall back plan if the sensor fails or if you don't agree with its values. I view the information as just another data point as opposed to the complete facts on the sorb. Similar to knowing your car's gas milage vs what does the fuel gauge say.

There are lots of great rebreathers out there. To me it is more of what your preferences are and how do they support it. The big debate is front vs back mount lungs. Having dove both - I prefer the back mount from cleaning up the clutter on the chest. There are drawbacks to the back mounted lungs (like the rEVO) that people will mention. That is. up to you on what you feel is important.

Good luck.

Eric
 

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