Review Diving the Avelo System

[lexvil]

I’m not deeply following this but in essence, as I’m getting it, you are not adding weight, since the water underwater is the same weight, instead you are reducing displacement volume. What is the total displacement swing available from a full tank on through nearly empty? What is the pressure rating of the bladder that you compress to offset volume?

 

[scubadada]

Hi @lexvil

Good questions. The 10 liter Hydrotank is rated to 300 bar/4350 psi. This includes the pressure change from pumping. The example given above by @jakeluther is a starting pressure of 270 bar and an increase to 290 bar after the first pump. An initial fill pressure of 270 bar/3915 psi would be about 95 cu ft of gas.

When my wife and I used the Avelo system in Bonaire, we used a single pump to become neutrally buoyant at the start of the dive. We added about one additional pump during the dive to maintain neutral buoyancy. Our tanks were only filled to about 3000 psi, so we started with about 73 cu ft of gas, a little less than an AL80 filled to the same pressure.

 

[lexvil]

Hi @lexvil

Good questions. The 10 liter Hydrotank is rated to 300 bar/4350 psi. This includes the pressure change from pumping. The example given above by @jakeluther is a starting pressure of 270 bar and an increase to 290 bar after the first pump. An initial fill pressure of 270 bar/3915 psi would be about 95 cu ft of gas.

When my wife and I used the Avelo system in Bonaire, we used a single pump to become neutrally buoyant at the start of the dive. We added about one additional pump during the dive to maintain neutral buoyancy. Our tanks were only filled to about 3000 psi, so we started with about 73 cu ft of gas, a little less than an AL80 filled to the same pressure.

It seems viable for nice warm water diving but for drysuit stuff, not so much without getting a max fill especially. Makes me wonder if a ridged ballast tank (like a submarine) wouldn’t be more effective using a small HP tank to blow ballast…

 

[inquis]

as I’m getting it, you are not adding weight, since the water underwater is the same weight, instead you are reducing displacement volume.

Displacement volume is constant. You are adding weight, even though it's in the tank -- mass is mass.

What is the total displacement swing available from a full tank on through nearly empty?

Realistically, ~3 kg (6.6 lb). A 200 bar air fill in a 10 L cylinder is 2000 bar.liters of gas. Pressurized to 300 bar, that gas takes up 6.7 L, leaving 3.3 L to be taken up by the water ballast.

This is reduced by any additional gas you take. The 270 initial fill for @jakeluther leaves room for 1 kg (2ish lb) of buoyancy change. The initial surface buoyancy will necessarily be no more than +1 to +2 kg (at end of a normal exhale, or up to +4.5ish lb) since a forced lung exhalation can drop up to a kg.

ETA: at the end of a dive to the equivalent reserve in a 500 psi AL80 (0.5 kg of air), the gas consumed adds 2.1 kg to the surface buoyancy. You might be up to ~4 kg (almost +9 lb) waiting for the boat. Inhalation will increase this, of course.

 

[lexvil]

Displacement volume is constant. You are adding weight, even though it's in the tank -- mass is mass.


Realistically, ~3 kg. A 200 bar air fill in a 10 L cylinder is 2000 bar.liters of gas. Pressurized to 300 bar, that gas takes up 6.7 L, leaving 3.3 L to be taken up by the water ballast.

This is reduced by any additional gas you take. The 270 initial fill for @jakeluther leaves room for 1 kg of buoyancy change. The initial surface buoyancy will necessarily be no more than +1 to +2 kg (at end of a normal exhale) since a forced lung exhalation can drop up to a kg.

First off, I’m old and I stupidly voted for Ronnie back in the day so as an American I am doomed to see talk of liters as applying to puppies and kittens, kg as an odd multiplier and bars as places to drink.

So I’m mentally disabled with such talk.

Do things float due to their weight or their volume?

 

[inquis]

Do things float due to their weight or their volume?

Yes.

 

[lexvil]

Yes.

Clears everything right up and without insulting the lmperial mindset.

 

[scubadada]

Do things float due to their weight or their volume?

Yes. The displaced weight of water, from the volume, vs. the actual weight of the object. If the object displaces more weight of water than it weighs, it floats. If it displaces less weight of water than it weighs, it sinks.

 

[inquis]

This is reduced by any additional gas you take. The 270 initial fill for @jakeluther leaves room for 1 kg (2ish lb) of buoyancy change. The initial surface buoyancy will necessarily be no more than +1 to +2 kg (at end of a normal exhale, or up to +4.5ish lb) since a forced lung exhalation can drop up to a kg.

As has been pointed out, weighting is crucial. If your rig is setup/weighted for a 3000 psi fill (buoyancy of +1 kg or 2ish lbs), and you are lucky enough to get a 3900 psi fill (@jakeluther's 270 bar fill), you will then be neutral to start -- head awash at normal exhale -- relying on top-of-the-lung breathing to keep your mouth out of the water.

Wetsuit compression then makes you negative at depth (without any water ballast at all) and must therefore be compensated with larger breaths until enough gas is consumed. Fingers crossed that CO2 retention headache doesn't set in.

I'm fairness, a normal rig has it's own issues with overweighting, as we all know. It's just something to be aware of.

 

[inquis]

I am well aware many of my posts on this topic seem to be critical of avelo, but that's mainly to give balance against the manufacture's view through (understandably) rose-colored glasses. In truth, I would totally dive this system in some situations, but I feel understanding both pros and cons is important.