Checklists in Rebreather Diving

[rddvet]

There is a difference between Open Circuit, with all the compromises that system imposes, and Closed Circuit which has a whole host of other compromises.

As mentioned, OC has valves up because of the weight of the cylinders. Commie divers invert them for ease of access to the valves, but have "dive butlers" to dress/undress them. Some people dive inverted doubles/twinset but this requires a protective stand around the valves to protect them when sitting on the bench.

A backmount CCR is completely different. For a start there's the low amount of oxygen and diluent which means 2 or 3 litre cylinders. The "box" includes a convenient scrubber unit to attach the cylinders (plus suit inflate, batteries, etc.) and normally has a stand as you don't want your fragile $£€10k+++ unit falling over. Most people can reach valves near their hips; not all people can contort themselves to twiddle knobs behind their head -- hence the endless valve drilling on twinsets/doubles.

As for the suggestion that I deliberately put the valves in the most vulnerable position -- behind my head -- is a crazy non-starter. The valves live near my backside just like all normal units. They're nicely tucked away from any danger; along with the hoses.


When diving on wrecks, you need to ensure that the top of the unit's as streamlined and tough as possible as you will -- not might, you will -- bash the wreck and any other fishing apparatus strewn over the wreck. Cave restrictions will be the same; bashing the top of the unit is not uncommon. Why are "cave shields" sold for JJs and other rebreathers?


Appreciate that we dive with what we have. Just making the point that some of the design decisions are common sense as CCR isn't OC.

How many times have you tried it? I'm assuming none. If the answer is none, then try it before lamenting over it being the wrong way of doing it.

BTW thank you for explaining the basics of rebreathers. I always wondered what the "box" was, but was afraid to open it cause it could have been Pandora's.

Anyway, if you don't like it so be it. It works, but you don't think it does. You've never tried it. But I've tried valves down. So I'd say go get the experience to be able to back what you say. Do you have cave training?

 

[Germie]

Is anyone running 7 litre / "LP50" onboard dilout cylinders with valves down? How does it dive & trim?

It's not surprising the DIR / GUE manifolded twinset CCR has the valves up. It might even trim the rig well. I'm not sure I would want two other additional valves right next to my oxygen valve, mixups could happen. But those upright valves are definitely asking for a beating. Maybe that's why they need all the extra valves

It probably makes sense for packing boat divers onto a high end boat (with a lift) since there's one less extra bailout cylinder to wrangle.

How much longer is the GUE CCR checklist?

The biggest problem in this picture is the weight of the configuration. I like my ccr because it is less heavy than my twin12, haha. Another problem with this in caves is that it is more bulky than a normal backmount ccr or twinset. I have seen people entering a cave with a normal JJ and that fits, but this configuration did not fit. In wide caves, this will also fit, as a twin20 also will do.

For boatdives, yes, this will work probably. But there are also disadvantages of this config over taking an extra bo cylinder. I would say as always take what works for the dive you want to make. But there is not a right or wrong.

 

[bubblemonkey2]

The biggest problem in this picture is the weight of the configuration. I like my ccr because it is less heavy than my twin12, haha. Another problem with this in caves is that it is more bulky than a normal backmount ccr or twinset. I have seen people entering a cave with a normal JJ and that fits, but this configuration did not fit.

For boatdives, yes, this will work probably. But there are also disadvantages of this config over taking an extra bo cylinder. I would say as always take what works for the dive you want to make. But there is not a right or wrong.

Agreed and I'll reason the JJ-CCR guys + substantial high-level diving community actually knew what they were doing when they designed the "stock" configuration, well before the Florida business decided to make their OC cultists keep diving a twinset config at all times, even on CCR.

But to get back on topic, how much more does it complicate the checklists?

 

[Germie]

Agreed and I'll reason the JJ-CCR guys + substantial high-level diving community actually knew what they were doing when they designed the "stock" configuration, well before the Florida business decided to make their OC cultists keep diving a twinset config at all times, even on CCR.

But to get back on topic, how much more does it complicate the checklists?

deploying a long hose in the water?

 

[Wibble]

How many times have you tried it? I'm assuming none. If the answer is none, then try it before lamenting over it being the wrong way of doing it.

BTW thank you for explaining the basics of rebreathers. I always wondered what the "box" was, but was afraid to open it cause it could have been Pandora's.

Anyway, if you don't like it so be it. It works, but you don't think it does. You've never tried it. But I've tried valves down. So I'd say go get the experience to be able to back what you say. Do you have cave training?

Tried what exactly? Turning my O2+dill tins upside down so the valves are in the wrong place for absolutely no benefit?

 

[Wibble]

Checklists in Rebreather Diving​

Where does that say CAVE DIVERS ONLY????

Obviously cave divers like to do things their own way for whatever made up reasons they want, then have a go at other people for the hell of it.


Adding to this, the OP mentioned a Revo, something that most of the above know sod all about, but love to spout opinions.

All rebreather divers should know one thing: all boxes** are different and have very different challenges. Even filling a scrubber is completely different according to the box, the scrubber and the rules.

The checklists, whether it written or mental, varies between the units.

• The build checklist: putting the unit together. Gas analysis, filling, don't forget that O-ring, etc.
• The closed checklist: testing that the unit's working, cells work/calibrate, ADV, pos/neg test, gasses programmed, etc.
• The turn the machine on and climb in it checklist: connected drysuit, gases on, prebreathe, bailout checks, etc.
• The pre-jump checklist; quick check to ensure you've buoyancy and the gas is breathable and on.

Where does that vary with a cave/mine/overhead/boat/wreck/shoredive/quarry?


And finally, WTF has anyone's cave diving experience got to do with any of this aside from being massively off topic?


** Boxes. A commonly used synonym for rebreather. Like unit. YBOD.

 

[rddvet]

Tried what exactly? Turning my O2+dill tins upside down so the valves are in the wrong place for absolutely no benefit?

And this is why people use the ignore button on you. You talk alot, but don't have the first hand experience to back it up. If you're going to talk badly about something, at least do us a favor and have actually tried it. There is no major negative to bottles down, just not my choice. There's also nothing wrong with bottles up, how I prefer. I personally find reaching valves are easy with valves up, it creates the same muscle memory as in backmount, it standardizes flow checks between oc and cc, and it helps trim the unit out well. I jump back and forth between bm oc and bm ccr. Muscle memory is important. If I hear a tank bubbling there's no hesitation. I reach to the same spot in bm and ccr. Bottles down would take a split second longer for my brain to make my hand go down not up.

Just an aside, how many people you know that put weights at the top of their unit because they're foot heavy, especially revo divers? Valves up is a solution to that issue.

But at the end of the day, you have no cave experience and have no valves up experience. So maybe rather than having diarrhea of the mouth and saying things that you have no experience with, just keep quiet and ponder the ways other people do things differently and maybe even try them. The guys that developed the fathom with valves up are much better divers and have much more experience than likely all of us in this thread. I'm sure if there was a better way, it would have been done or trialed. Just because something is "always done that way" doesn't mean it always has to be done that way.

 

[Wibble]

It probably makes sense for packing boat divers onto a high end boat (with a lift) since there's one less extra bailout cylinder to wrangle.

Not to mention having replacement 7's for different mixes. Have heard that they're difficult to switch on the units, unlike on a normal unit where the 3 litre diluent is trivial to change. A pair of spare 7's with the Lola (?) valves would be a lot more expensive than one spare 3 litre cylinder as per a normal backmount CCR unit.

 

[Wibble]

And this is why people use the ignore button on you. You talk alot, but don't have the first hand experience to back it up. If you're going to talk badly about something, at least do us a favor and have actually tried it. There is no major negative to bottles down, just not my choice. There's also nothing wrong with bottles up, how I prefer. I personally find reaching valves are easy with valves up, it creates the same muscle memory as in backmount, it standardizes flow checks between oc and cc, and it helps trim the unit out well. I jump back and forth between bm oc and bm ccr. Muscle memory is important. If I hear a tank bubbling there's no hesitation. I reach to the same spot in bm and ccr. Bottles down would take a split second longer for my brain to make my hand go down not up.

Aside from a truckload of extra money to buy the cylinders plus pointless modifications to a unit to solve a problem that doesn't exist.

But there's no point in arguing here: you're happy with your way, for that I salute you. Your way doesn't suit other people's needs, something you'll have to accept.

Just an aside, how many people you know that put weights at the top of their unit because they're foot heavy, especially revo divers? Valves up is a solution to that issue.

Have no idea what you mean by this. My Revo's perfectly balanced. I have 2 to 2.8kg on the top in the sea (summer/winter) and 0 or 1kg in fresh water (depending on temperature, i.e. underclothes). It's literally open the velcro and throw in the correct weight -- actually part of the checklist.

But at the end of the day, you have no cave experience and have no valves up experience. So maybe rather than having diarrhea of the mouth and saying things that you have no experience with, just keep quiet and ponder the ways other people do things differently and maybe even try them. The guys that developed the fathom with valves up are much better divers and have much more experience than likely all of us in this thread. I'm sure if there was a better way, it would have been done or trialed. Just because something is "always done that way" doesn't mean it always has to be done that way.

Make up whatever you want... You don't dive with me, nor I with you. You don't know my background either as you ass-u-me many wrong things.

"Valves up" (meaning a pair of 7 litre soft-manifolded diluent+bottom bailout cylinders and specialist "H" valves) obviously suit your specific diving profile and works on your unit.

It is hard to see how the additional unit weight (55kg over 40kg from a previous thread -- significant if you're carrying the thing over ground to the dive site and especially if there's a low ceiling in the cave), plus the additional OC regulators (longhose and necklace), special techniques (must come off loop to donate longhose) and INflexibility (can't change diluent easily) would be better choice than a 3 litre diluent and standard bailout with a longhose.

Out-of-gas: have my longhose bailout reg on my ready-and-waiting bailout; in fact have the whole cylinder so we're not attached by a longhose. Out-of-gas at shallow, have my deco bailout -- the same donate process.

Ultimately this will all be moot. No doubt the future is bailout rebreathers. With twice the checklists.

 

[rjack321]

What does any of this valve up vs down blathering have to do with checklists?