Northwest Dive Club

I have to say, the one that caught my interest was the Poseidon Discovery/Cis-Lunar unit. There are some very interesting and different things about its design, in particular how it uses its two O2 cells. I had read Andrew Ainslie's piece about voting logic in cells, and this looks like a very intriguing way to avoid some of the problems that input from three cells can cause.

I wasn't able to do as much research on the CCR's as I had hoped. I did talk to Peter at Tacoma Scuba's booth and he did a show-n-tell on the KISS Sport. I looked very interesting. I Liked the simple, mechanical concept. Maybe someday!

Thanks for the links Lynne. Nice side by side comparison of the basic differences between the most common units.

Joshua Smith wrote:Must say, though: that particular piece of clothing looks way, way better on my wife than it does on Pez.

Not a fair comparison, I still had my shirt on!

How often, does your average CCR diver call a dive because of some "technical" issue with the unit? I can think of at least three occasions that I've witnessed myself on three different models. Is this common? Is it user error? What issues will keep you out of the water?

Pez7378 wrote:

Joshua Smith wrote:Must say, though: that particular piece of clothing looks way, way better on my wife than it does on Pez.

Not a fair comparison, I still had my shirt on!

How often, does your average CCR diver call a dive because of some "technical" issue with the unit? I can think of at least three occasions that I've witnessed myself on three different models. Is this common? Is it user error? What issues will keep you out of the water?

I have not seen many if any dives called because of equipment issues, usually if that did happen it would be because the user did not do a proper pre-dive check of the equipment or did not perform the needed maintenance on their unit. The reliability of the equipment is greatly dependent on the user doing their job properly.

The more complicated the rebreather and the more possible failure points, the greater chance of a problem, good electronics redundancy also helps with the ability to continue a dive is something fails.

Pez7378 wrote:

Joshua Smith wrote:Must say, though: that particular piece of clothing looks way, way better on my wife than it does on Pez.

Not a fair comparison, I still had my shirt on!

How often, does your average CCR diver call a dive because of some "technical" issue with the unit? I can think of at least three occasions that I've witnessed myself on three different models. Is this common? Is it user error? What issues will keep you out of the water?

I've only had to scrub 1 dive due to issues with my unit- an 02 cell failure. Out of, I don't even know how many dives, but I've been diving it for a year and a half now. Maybe 150 dives?

Joshua Smith wrote: I've only had to scrub 1 dive due to issues with my unit- an 02 cell failure. Out of, I don't even know how many dives, but I've been diving it for a year and a half now. Maybe 150 dives?

In six+ years of rebreather diving, I think I've scrubbed only one dive on the Evolution, ever, because of the unit. I had one of a bad batch of handset LCDs and pushed it and dove anyway; after about 20-30 minutes underwater, the handset eventually because unreadable, and I had to finish up the dive. Sent it back to APDiving, and it was repalced free of charge, even though the unit was two years post warranty. Perfectly safe to keep diving the unit, as the controller kept right on chugging just fine, but an annoyance, as I had to rely on my VR3 for deco/timing info.

I've had a few delayed dives because of a bad O2 cell, or something stupid like not checking the batteries prior to going to the dive site and needed to pause and change one before I get in the water. O2 cells and spare batteries are up there with O-rings in the save-a-dive kit.

On an old Drager unit which I had for a couple of years, I scrubbed quite a few -probably around 6 a year, I'd say. The Drager mouthpieces are poorly engineered and they dry out after a while which causes them not to hold neg/pos pressure...gurgle, gurgle. I also flooded the unit on a number of occasions - pinholes in the lungs, nick in the scrubber rim sealing surface, p-port springs on the clips that wore out and didn't engage fully, unsealing underwater, etc. There were a couple due to the crappy electronics that Uwatec puts out. Their Aladdin AirZ O2+Oxy2 combo never did work quite right, flooded several times, and ultimately lead to my decision to NEVER, EVER dive a piece of Uwatec gear again. (In fairness, the factory replaced the transmitter 3x and the handset 2x, but that's not a good track record for life support.) For those not in the know: while the Drager is a semi-closed unit, it's fundamentally similar in how it works to an mCCR, and if you cut the cut the flow dramatically, use pure O2, and plumb a second dil bottle into the loop, then it's identical to a KISS style mCCR.

So, I've scrubbed a lot of manual unit dives, but only one electronic unit dive (and I'm now well into year 4 of eCCR time.)

I chose the Sport Kiss for its simplicity and mainly for its size. I travel frequently with this rig, and I can fit it nicely in my roll-aboard carry on.

'nough said.

cheers,

RBN

Pez7378 wrote:...

How often, does your average CCR diver call a dive because of some "technical" issue with the unit? I can think of at least three occasions that I've witnessed myself on three different models. Is this common? Is it user error? What issues will keep you out of the water?

We've had whole dive trips screwed because of electronics issues that couldn't get resolved in remote locations but I do think we had exceptionally bad luck with our first rebreathers even though we took exceptional care of them. We switched style and type of rebreather and haven't missed a dive yet, we like to think it's because we switched to a manual set up but who knows, there are plenty of happy eCCR divers out there.

g

Well this is coming (obviously) from a complete layman so maybe this is a stupid question but CCRs seem to be really pretty basic in their design. It doesn't really seem like there's a whole lot to them that couldn't be swapped or fixed with little more than a Leatherman and some spare parts at the dive site. Does it have alot to do with the users mechanical apptitude/diagnostic skills?

Most CCRs are basically pretty simple. Most of them can be taken most of the way apart without any tools. Of course, there are usually electronics and computers involved, too, which raises the stakes. I'm not sure what your question is, exactly- did that help?

Mattleycrue76 wrote:Well this is coming (obviously) from a complete layman so maybe this is a stupid question but CCRs seem to be really pretty basic in their design. It doesn't really seem like there's a whole lot to them that couldn't be swapped or fixed with little more than a Leatherman and some spare parts at the dive site. Does it have alot to do with the users mechanical apptitude/diagnostic skills?

Mattleycrue76 wrote:Well this is coming (obviously) from a complete layman so maybe this is a stupid question but CCRs seem to be really pretty basic in their design. It doesn't really seem like there's a whole lot to them that couldn't be swapped or fixed with little more than a Leatherman and some spare parts at the dive site. Does it have alot to do with the users mechanical aptitude/diagnostic skills?

that is an astute observation, in basic concept, they are remarkably simple. It's a desire for hands free function that has lead to them being, IMHO, unnecessarily complex, at least for what the average diver is doing with them.

the more integrated and complex the electronics are, IMHO, the more likely an issue with one element will trip up the whole system.

I like a rebreather that has a dedicated primary computer and isolated battery, devoted exclusively to po2 on at least 3 cells (with no set point controller). In my set up, that computer is the shearwater HUD, giving me real time po2 all the time on all three cells. I'd have no problem with the secondary being integrated with all sorts of functions, co2, deco, temp stick, maybe even a set point controller... for now my secondary shows po2 and deco and that's it. o2 injection is all manual and MFO. simplicity to me is relative to primary importance, and that is po2, the rest is just icing on the cake and best left to the secondary, as long as you can cross check po2 periodically on the secondary and still get po2 if the complex system has a melt down. That said, I'd now be happy with two po2 only sytems (with a total of 4 cells, 2 devoted to each) and off board deco. As I now have had lots of dives with in-line deco and off board at the same time and the deco comes out nearly identicle on every dive between computers, and that's diving manually with a max of 30 mins deco.

I think the KISS was the first rebreather to hit the nail on the head in this respect, although I prefer the copis or rEvo.

it took me quite a while to realize just how simple a rebreather actually can be. Simplicity is a beautiful thing when it comes to life support and in field repairs!

g

Gill Envy wrote:

Mattleycrue76 wrote:Well this is coming (obviously) from a complete layman so maybe this is a stupid question but CCRs seem to be really pretty basic in their design. It doesn't really seem like there's a whole lot to them that couldn't be swapped or fixed with little more than a Leatherman and some spare parts at the dive site. Does it have alot to do with the users mechanical aptitude/diagnostic skills?

that is an astute observation, in basic concept, they are remarkably simple. It's a desire for hands free function that has lead to them being, IMHO, unnecessarily complex, at least for what the average diver is doing with them.

the more integrated and complex the electronics are, IMHO, the more likely an issue with one element will trip up the whole system.

I like a rebreather that has a dedicated primary computer and isolated battery, devoted exclusively to po2 on at least 3 cells (with no set point controller). In my set up, that computer is the shearwater HUD, giving me real time po2 all the time on all three cells. I'd have no problem with the secondary being integrated with all sorts of functions, co2, deco, temp stick, maybe even a set point controller... for now my secondary shows po2 and deco and that's it. o2 injection is all manual and MFO. simplicity to me is relative to primary importance, and that is po2, the rest is just icing on the cake and best left to the secondary, as long as you can cross check po2 periodically on the secondary and still get po2 if the complex system has a melt down. That said, I'd now be happy with two po2 only sytems (with a total of 4 cells, 2 devoted to each) and off board deco. As I now have had lots of dives with in-line deco and off board at the same time and the deco comes out nearly identicle on every dive between computers, and that's diving manually with a max of 30 mins deco.

I think the KISS was the first rebreather to hit the nail on the head in this respect, although I prefer the copis or rEvo.

it took me quite a while to realize just how simple a rebreather actually can be. Simplicity is a beautiful thing when it comes to life support and in field repairs!

g

That is why i like my rEvo mCCR you really cannot get any simpler in design than that.

As far as electronics go I imagine that O2 sensors and maybe electronic solenoids would be the main culprits?

certainly 02 censors are dodgy, thus three and sometimes four are used, hoping that only one goes at a time. I've watched them decay, mostly in plenty of time to replace them, but what i've witnessed in just 3 years has been eye opening, on occasion they fail suddenly or even worse, they act up intermittently!

while solenoids have common issues, while two set point controllers are common, only one solenoid is typical, creating a common failure point for many eCCR's. Of course using multiple solenoids would be problematic. Some folks are adding redundancy in o2 addition by adding a MFO to an eCCR, though then you have issues with IP (i'm not sure how that's handled).

g