Important features when choosing a rebreather

[kensuf]

On the ADV front, I don't think it is necessary for all units, but that will depend on the CL/loop design and volume.

On the Scrubber Life Monitor, yeah I agree stack timers are good, BUT even more important than that, is good diver habits - a scrubber with 3 hours on it that has a 6 hour theoretical life is not something I would take on a 250' dive.

On the CO2 monitor - by the time you get hypercapnia, you're screwed.

My list would have:

Dual monitoring - including either a HUD or haptic feedback
Simplicity of design - the simpler the design, the less chance for crap to break
BOV - I'm a fan of BOV's, plus they work great for adding DIL in a pinch

 

[AJ]

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.

Agree. If it's reliable it's an asset. If not, don't bother. But still, scrubber duration is not the only factor to be concerned about. If sorb is packed for too long without diving it, scrubber time can be ok but you better not use anymore. Therefore fill date and scrubber use time seem the most important factors to me which can easily be recorded without electronics.

An CCR is complex enough as it is without electronic gimmickry if you ask me. Keep it simple is my motto.

 

[tbone1004]

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?

ADV-like @Bobby and others have said above, I have a love-hate relationship with ADV's. I hated the plunger style ADV on my Meg as an ADV because it almost never worked properly, can't stand the t-piece style ADV's because they are prone to leaking and always fire when you don't want them to, but I love the concept of an ADV and for the initial descent it is quite nice. I do not use it other than rapid descents and prefer to have a shutoff since I prefer to dive a min-loop volume that is probably a smidgen past minimum and they trigger. My sidemount unit does not have a shutoff on the ADV, but it is positioned in a way that it is not terribly annoying.

Scrubber Monitor-again, great in theory but not so great in practice. They are only ever so accurate and while it's "nifty" to have, I do not know that I would recommend having it as a buying criteria.

CO2 is the "holy grail" but like @kensuf said, once it measures CO2, it's likely too late.

My list in what I believe is the order you should be whittling down the list

General Configuration-backmount, sidemount, rack compatible, etc. If you have a need for one of those configurations, it is going to seriously narrow the list. I need a sidemount unit for most of my cave diving which makes the list really short, and for my ocean units I greatly prefer a rack. For the backmount units it rules out the O2ptima, Revo, and KISS units because they aren't compatible with that configuration. Make this decision first and see if it narrows the list down at all, for most rebreather divers it may not.
eCCR/mCCR-all eCCR's can be made into hCCR's pretty easily so if you decide you really like the hCCR concept, it's a very easy addition.

The rest of these may whittle the list down, but most of them can be changed with 3rd party "kits" so it is not necessarily a deal breaker.
Counterlung configuration- BMCL, TOS, OTS, integrated. I love the way OTS lungs breathe, but I can't stand the clutter so my general preference would be to BMCL or integrated lungs
BOV vs. DSV-I much prefer good BOV's and some of them have the added benefit of doing double duty as an ADV. Again, my current primary unit has a DSV but we haven't really sorted out a good sidemount BOV yet. When I dive backmount, I LOVE my Poseidon BOV and I think that a BOV on a backmount unit is a huge improvement in safety.

 

[tbone1004]

Agree. If it's reliable it's an asset. If not, don't bother. But still, scrubber duration is not the only factor to be concerned about. If sorb is packed for too long without diving it, scrubber time can be ok but you better not use anymore. Therefore fill date and scrubber use time seem the most important factors to me which can easily be recorded without electronics.

An CCR is complex enough as it is without electronic gimmickry if you ask me. Keep it simple is my motto.

One of the recent studies begs to differ with scrubbers staying packed for too long losing their capacity.
Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters

 

[flymolo]

an adv is not really necessary. if you have a bov, you can open it a little on descent and it will function just like an adv.

having an easy way to plug in off-board gas should be on the list as well...

 

[Wibble]

ADV thoughts.

Understand the resistance to an ADV and, certainly on some units they're unreliable.

Sometimes you've got too much going on and it's really useful; double-handing down a shotline whilst trying to free your torch/whatever. It's better to make a big inhale and suck the diluent into the loop than let go and squeeze the manual add button. Most frequently caused through not thinking forward enough.

Sometimes nice to set minimum loop volume with a deep inhale.

(Obviously numpty opinions)

 

[broncobowsher]

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?

You are only scratching the surface.

ADV is great for descent. You are typically task loaded fairly well during descent with watching PPO2, drysuit squeeze, keeping track of the team, making sure there are no issues with yourself or others you are with. The ability to hit that brick wall, suck a little harder and get some dil without adding another task to your hands.

Scrubber life monitor. So many don't have this and it isn't an issue. Don't see this as a show stopper. When I got my rEvo the RMS had an exceptionally high failure rate. Both myself and my instructor decided it wasn't worth it. More of a feature to say you can get more life out of a scrubber. Oh, the monitor says I have plenty of life, keep using it. With the rEvo it is easy to dump one scrubber and not really be wasting much. And you have plenty of scrubber.

Which leads to CO2 monitor. As others stated, a too late alarm. Add in the sensors don't work well in a rebreather. No one has made a good dive CO2 sensor so far.

The holy grail that looks viable in the future is probably the solid state O2 sensor.

Dual scrubbers are not a rEvo exclusive. Some KISS and another very small (and I think defunct) brand also use them.

As for choosing a rebreather, ease of maintenance should be considered. If you plan to travel with it, how well does it travel? Counterlung design was a huge one for me. You get a hot mess of hoses, bottles, etc. when you dive. If you can get some of that stuff (like counterlungs) out of your way it is a good.
One thing I had not looked at until I was shopping was counting the number of seals. Some models look like they are trying to add failure points by adding more and more O-rings, seals, hose ends, etc. to the rebreather. Trying to minimize these reduces your chances at a leak.
Another thing to look at is dead space.

And we have not gone into local support. Or a host of other considerations.
I will avoid the "buy from me and get free training", or the local shop is making me a deal on this. Getting the wrong rebreather to save a few bucks up front will still be getting you the wrong rebreather.

 

[AJ]

One of the recent studies begs to differ with scrubbers staying packed for too long losing their capacity.

I know, I read it. It takes more than just putting the scrubber aside. Apparently you need to vacuum the scrubber in an air tight bag which means careful procedure and tools. So under the right circumstances it's doable, but you need to be cautious I guess. Same story as with all the rebreather stuff: be careful and be cautious or it will bite you.

 

[tbone1004]

I know, I read it. It takes more than just putting the scrubber aside. Apparently you need to vacuum the scrubber in an air tight bag which means careful procedure and tools. So under the right circumstances it's doable, but you need to be cautious I guess. Same story as with all the rebreather stuff: be careful and be cautious or it will bite you.

there wasn't a huge difference in the "sitting on the shelf" results though, and I think you would be just fine if you put it in a drybag and sealed it. Get as much air out as you reasonably can and seal it and I bet the results are indistinguishable from the "vacuum sealed" results.

 

[Wibble]

Is a sealed Tupperware box OK? Once the CO2's been scrubbed from the surrounding space in the tub, that's it?