Question Bailout gas configs for tech/deep chestmount rebreathers

[inquis]

Since the unit would be run in a dil-out configuration, I'm assuming you get around the issue by being able to use both bailout cylinders to drive the unit in the chance you lose one?

On the Fathom, left post is dil, right post is long hose (manifolded). If left dies, add dil via LH inhale. I suppose you could add a drive whip to the right post, but that's another failure point -- personal call. For OW only, I'd skip the spare whip. For cave, I'd add the spare whip enabling a normal process on an up & down exit. For SM/cave, a stuffed second stage on the left bottle seems prudent to retain BO in case the right dies.

it seems the common practice is to use the onboard diluent cylinder for wing/suit inflation while using offboard gas to drive the unit

Fine for most caves. I'd want wing & suit separate for a hot drop over an abyss.

 

[Cio]

@Cio interesting point on an H valve. Does in theory address the loss of gas issue from a single cylinder. Is anyone doing that?

H valve does not address the loss of gas but the failure of a reg. Brian Kakuk, I saw, uses an h valve on his 1 dilout bottle for redundancy.

 

[whynot]

What experience do you have with a CM?

ETA: come to think of it, how many of the CM detractors actually have any time on one?

Drinking bleach is bad, and one doesn't need to first drink some bleach to know that they shouldn't.

 

[lostsheep]

Drinking bleach is bad, and one doesn't need to first drink some bleach to know that they shouldn't.

Got it, you have zero actual knowledge, you’re just talking out of your ass and grasping for straws.

Shirley you can do better than that?

 

[PfcAJ]

Got it, you have zero actual knowledge, you’re just talking out of your ass and grasping for straws.

Shirley you can do better than that?

A reasonable person can absolutely look at an equipment config and see its pros and cons without subjecting themselves to diving it.

Ridiculous to assert otherwise.

 

[lostsheep]

A reasonable person can absolutely look at an equipment config and see its pros and cons without subjecting themselves to diving it.

Ridiculous to assert otherwise.

Cool, then make an explicit assertion. The reticence here is deafening.

Allow me to demonstrate:

I assert that a CM unit with BM doubles of deep dilout and slung deco bottles functions identically to BM heavy configurations with the added benefits of easy scalability and utilizing standard OC gear.

 

[PfcAJ]

Cool, then make an explicit assertion. The reticence here is deafening.

Allow me to demonstrate:

I assert that a CM unit with BM doubles of deep dilout and slung deco bottles functions identically to BM heavy configurations with the added benefits of easy scalability and utilizing standard OC gear.

I don’t disagree buddy.

I just think that CM breathers put the thing in the worst place possible

 

[grantctobin]

I assert that a CM unit with BM doubles of deep dilout and slung deco bottles functions identically to BM heavy configurations with the added benefits of easy scalability and utilizing standard OC gear.

Zooming out a bit on this thread, I don't actually think that part is that contentious, ignoring any "there's stuff on my chest" and the large number of people that never seem to figure out how to get the lower half of their Choptima in line with their bodies.

Schools of thought that have been presented:
-Dilout with a manifolded or non manifolded pair of bailout breathable at appropriate densities and PPO2s at your deepest depth (JJ in a rack, Fathom in a rack, Choptima with doubles, sidemount bailout, what have you) with offboard deco bailout (let's assume 21/35, 50%, 100%)
-Standard BM unit with onboard dil, some number of offboard bottles for bailout and deco (let's assume 10/70, 21/35, 50%, 100%)
-Independent, non manifolded doubles on the back of different mixtures with some number of offboard bailout. We can potentially combine this with the @LFMarm discussion of four separate AL80s, one of which containing a mix breathable at the bottom. Say the same 10/70 21/35 50% 100%
-Manifolded doubles on the back with a mixture that is not breathable at max depth containing and intermediate mix. Single slung bottle of deep bailout. I think Justin Judd references 21/35 in the BM doubles in this article: Gas Planning With a Chest-Mounted Rebreather which Ben references.

Methods 3 and 4 suggest the use of only a single first stage that can deliver either bailout open circuit or a diluent feed into the unit. In the event of failure of the first stage, stay on the loop and ascend to the first breathable gas and plug in. In the event of failure of the unit, bail to this regulator and finish ascent.

There is also a variation that @kierentec suggested, which is actually closer to option 2 than it is option 4. Both the drive bottle for the unit (in his example, 21/35 drive, 32% bailout) are breathable and appropriate at max depth.

Deterministic questions:
-How much volume of deep bailout is needed? (within this, linear penetration distance? is free ascent possible? can you stage bottles? Do you make an estimate of 5min at deepest depth with heavily elevated RMV?)
-Is it within the diver's risk tolerance to rely on a first stage (or single cylinder o-ring) for deep dil + bailout?
-Does an H or Y or Lola Valve change the answer to the above question? Single dip tube, two dip tubes?)
-Do volumes line up across gasses?
-Can you stage gas? Is there a support team? Habitat?

 

[justinthedeeps]

H valve does not address the loss of gas but the failure of a reg. Brian Kakuk, I saw, uses an h valve on his 1 dilout bottle for redundancy.

How else is the gas lost?

I thought the top gas loss issue was a free flowing reg, since they are 'designed to fail that way.'

Manifolded cylinders let you close a valve (failed reg) and still save and access the gas. Otherwise we would just band cylinders together with no manifold.

Does an H valve not do the same, but for a single cylinder?

 

[Learner Diver]

80% is a trash gas.

How so?