Review Diving the Avelo System

[lowwall]

It doesn't work that way. After the initial pumping of ballast water, you are neutrally buoyant, and it is depth independent. You pump some more ballast when you become light from breathing down your gas.

Experienced divers like yourself can handle a few pounds of positive or negative buoyancy with breath control and perhaps some subconscious finning, so it makes sense that you only need to add some ballast once or twice during the dive. But I'm curious how often inexperienced divers will be hitting the buttons as they try to deal with small changes in buoyancy from wetsuit compression/expansion and the gradual increase in positive buoyancy from breathing down the gas.

You can certainly see a big difference in how often the inflator and dumps are used by experienced versus novice divers with conventional BCDs or wings.

 

[arkstorm]

So if the ballast water compresses the air bladder (thus decreasing its volume and increasing its pressure), how do you know how much air you have left without completely purging the system and making yourself positively buoyant in the process?

 

[scubadada]

So if the ballast water compresses the air bladder (thus decreasing its volume and increasing its pressure), how do you know how much air you have left without completely purging the system and making yourself positively buoyant in the process?

The Avelo mode on the computer gives you the % of gas remaining. Otherwise you calculate % remaining from the boosted pressure, Avelo provides a slate if you do not want to do the math.

 

[arkstorm]

The Avelo mode on the computer gives you the % of gas remaining.

How is that calculated?

Is that precise or an estimation?

 

[Dan]

How is that calculated?

Is that precise or an estimation?

You are referring to the air remaining in the bladder (annulus part of the cylinder), not the breathable air in the aluminum cylinder inside the carbon-composite hydrotank, right?

 

[Still Kicking]

You are referring to the air remaining in the bladder (annulus part of the cylinder), not the breathable air in the aluminum cylinder inside the carbon-composite hydrotank, right?

Ballast water is pumped into the bladder and the pressure of the breathable air increases.

 

[Dan]

Ballast water is pumped into the bladder and the pressure of the breathable air increases.

I guess I misunderstood the concept. I thought the breathable air is independent of bladder pressure as that breathable air is coming from aluminum cylinder inside of that carbon-composite hydro tank. So, the breathable air is like the normal SCUBA tank, except smaller diameter & taller plus rated at 300 bar instead of at 200 bar for normal SCUBA tank.

 

[Still Kicking]

I guess I misunderstood the concept. I thought the breathable air is independent of bladder pressure as that breathable air is coming from aluminum cylinder inside of that carbon-composite hydro tank. So, the breathable air is like the normal SCUBA tank, except smaller diameter & taller plus rated at 300 bar instead of at 200 bar for normal SCUBA tank.

I think I was wrong -- I think the water is pumped into the tank and the air bladder is compressed. Either way, the air pressure varies with the amount of ballast.

 

[Wibble]

I see a potential advantage to photographers. Having neutral buoyancy without depth dependence could save critical time and effort in setting up "the shot".

Or use any Buoyancy Control Device for neutral buoyancy.

Maybe someone could develop a BCD that doesn’t need batteries, electronics and a water pump to vary the gas volume within a bladder.

In engineering, simple always prevails over complexity.

 

[Dan]

I think I was wrong -- I think the water is pumped into the tank and the air bladder is compressed. Either way, the air pressure varies with the amount of ballast.

Avelo has the following sketch of the hydro tank (as shown, below). The bladder is in between the OD of aluminum breathable cylinder and the ID of carbon composite hydro tank. As you pump water into that annulus space you displace the volume of the bladder, squeezing the bladder into smaller volume, hence, increasing the air pressure in the bladder. And from what I understood the hydro tank pressure is slightly higher than ambient pressure so you can purge some out later if you over pump it, hence, the water pressure would be slightly higher than at whatever depth you are in. If you are at 30m, the hydro tank pressure would be slightly greater than 4 bar, which is much lower than the 300 bar for the breathable air from the aluminum tank inside the hydro tank.

The air bladder is just there to keep the water from sloshing around the cylinder and shifting the system weight around.

The main difference between Avelo system and the regular BCD are:
1. The buoyancy device for Avelo is in a rigid form (between the aluminum tank & hydrotank). While BCD is flexible like a balloon.
2. Water is used for ballast in Avelo system and air is used for ballast in BCD.
3. No battery, water pump, electronic is required in BCD system (KISS design).