Opinions on separate Wing inflate (drysuit inflation bottle?)

[Wibble]

Had a moderately deepish dive today which was using a rich diluent mix.

Descended down the shot line and inflated the wing when I reached the wreck. It's winter temperatures (11C/51F) and I want to be a little bit overweighted so I can fluff up my drysuit during the decompression. Also need to counteract the bailout gas and the SMB reel, etc.

Following on from our recent "helium is so rare and expensive" discussions, it struck me that this is such a waste of diluent -- I used about 40 bar for the whole dive, a large chunk of this for filling the wing for buoyancy at the bottom and on the surface. Got me thinking... what are the alternatives?

Do please pile in on these ideas!
N.B. a little Revo centric.

1) Use air as the diluent in the "standard" diluent cylinder. Use offboard rich helium gas for the bottom portion of the dive (possibly from the bailout cylinder)
Pros:

• Little rigging effort: just connect bailout to offboard gas connector and run manually
• Once back at deco depths has a decompression benefits as no helium in diluent -- one dil flush will empty the loop of helium (only the exhaled off-gas)

Cons:

• Must take care to not use the air diluent deep --
  1.1 (target PPO2) / 0.21 (fraction O2 in air) = 5.24ATA = 42m/137ft.
• ADV will use the air diluent. Bad if deep. Will need to disable the ADV (not easy on a Revo, standard on many other units).
• Bailout is more likely to be a standard gas which isn't compatible with diluent PPO2 rules (1.1 rather than 1.4)
• Bailout is consumed -- will need to be pumped up post dive
• Must remember to inject using the correct diluent (offboard not onboard diluent)

2) Inflate the wing from a different gas source, e.g. suit inflate
Pros:

• Doesn't interfere with the loop gas.
• Simplest: nothing to remember for ADV, manual diluent injection, solenoid
• Works with eCCR, don't need to run unit manually
• Easy to configure: run a second tail up from the suit inflate over the unit and down the elephant's trunk.

Cons:

• Redundant buoyancy relies upon separate systems; this means both drysuit and wing are inflated from one supply: one cylinder, one first stage, double the use of gas.
  • Can connect a (deco) bailout to provide suit inflate, even connect to the wing
  • Could have a disconnected tail from the diluent run down to the wing inflate ready to be switched over if suit inflate fails/empty
• Will need a larger suit inflate: the small 1 litre 200bar/7cf? won't cut it.

Seems the second option has fewer drawbacks.

Are there other options?

 

[mr_v]

I have been diving dry almost as soon as I finished my AOW. Curious, why would you use wing at all? I've always relied on my drysuit as the main source of buoyancy compensation. Not saying that my preferred way is better, so please pardon my curiosity.

Given the options above, I prefer #2, but I'd use the wing only if there is a drysuit failure, e.g., a catastrophic flood. Also, cut the off ADV air supply

 

[Heat Miser]

Solenoid will use the air diluent. Therefore have to run the unit manually.

My Solenoid valve is mounted to my oxygen line.

Something I learned on my MOD 2 course SANTI don't recommend inflating your drysuit with rich PPO2 mixes (say Nx 50 offboard) because it can cause oxidation on the glue.

 

[Wibble]

My Solenoid valve is mounted to my oxygen line.

Thanks for pointing that out. My bad!
Have edited and removed that (incorrect) line.

Something I learned on my MOD 2 course SANTI don't recommend inflating your drysuit with rich PPO2 mixes (say Nx 50 offboard) because it can cause oxidation on the glue.

Interesting. Didn't know that.

Connecting the drysuit to the (lowest, non helium) bailout stage would probably mean the 50%. It should just be for the case where the suit inflate's failed, so not a regular occurrence)

 

[Wibble]

I have been diving dry almost as soon as I finished my AOW. Curious, why would you use wing at all? I've always relied on my drysuit as the main source of buoyancy compensation. Not saying that my preferred way is better, so please pardon my curiosity.

The theory says that you need enough weight to overcome all disposable buoyancy. This means breathing gasses and also heavy reels, lift bags with built-in inflation. For OC twinset+multiple stage cylinder diving this can be a surprising weight of gas.

For CCR the O2 and diluent weight is negligible, but you must include the weight of bailout gasses: you don't want to bail out and find you're too light to hold your deco stop because your bailout & deco gas has been consumed.

I've always dived using the wing as the course control and the drysuit for comfort and a small amount of buoyancy adjustment. At deco I like to have more gas in the drysuit as it's a bit warmer.

 

[Marie13]

Thank you for bringing this question up. Made me think about what I’d do once I have my unit, although it will be a while before I’m doing Trimix.

 

[acxc]

I asked the same questions when I switched over to a rebreather. I hated wasting helium into a wing and tried to come up with any way to avoid that. In reality I realized I was putting so little gas into my wing, if at all, that it wasn't worth worrying about. If i do get light, getting rid of any extra gas in my suit and loop more than takes care of it.

That said, I have a buddy that dives a revo and did exactly what you described- steel 9cf inflation bottle, pumped up a bit, mounted in his stand. Inflator hoses running to both wing and drysuit, with a spare from his Dil running down that wing hose as a back-up if the inflation bottle runs out. Works really for him.

 

[Wibble]

I use a 232 bar 2 litre suit inflate cylinder.

(232 x 2 = 464 litres / 28 = 16.5cf)

Big enough for several dives.

 

[Jonn]

If you’re going to use a dedicated bottle for the suit and wing, might as well put argon in it. Better than helium anyway.

 

[grantctobin]

If you’re going to use a dedicated bottle for the suit and wing, might as well put argon in it. Better than helium anyway.

Except doesn’t have tangible benefit over air unless you’re flushing the suit several times before the dive…