Although scuba divers may appear to be "as free as a fish," they're actually loaded down with quite a bit of gear. The Avelo System is designed to help in that regard, as it moves the functionality of the buoyancy compensator into the air tank, making the former unnecessary.
Ordinarily – along with a wetsuit, fins, mask and snorkel – divers wear equipment that includes a compressed air tank, regulator, weight belt and buoyancy compensator device (BCD).
The latter takes the form of a big inflatable yoke-like vest, which is used to maintain neutral buoyancy. If the diver needs to increase their buoyancy, they transfer a bit of air from their tank to the BCD – they decrease their buoyancy by purging air from the BCD into the water.
As an air tank becomes increasingly empty throughout the course of a dive, it becomes more buoyant. Releasing air from the BCD helps divers compensate, although they also require a fair amount of weight on their belt to keep them from popping up to the surface.
The Avelo System is claimed to eliminate the need for a BCD, and to greatly reduce the amount of weights required. It's also said to make maintaining neutral buoyancy much easier.
The setup still incorporates a tank, but that tank consists of a carbon fiber shell with an expandable air bladder inside. An electric pump and purge valve are located to one side of the tank, while a battery is located to the other. All of the components are mounted on a backpack-type platform, as is the case with traditional scuba tanks and BCDs.
Before a dive, the air bladder is filled via a standard compressor, up to a maximum pressure of 4,350 psi (300 bar). At that point, the bladder fills the inside of the tank. Once the diver is in the water and ready to descend, they gradually pump water into the tank. The bladder compresses up to the top of the tank as it's displaced by the water at the bottom – at the same time, the added water makes the tank heavier, and thus less buoyant.
As the dive progresses and the air in the bladder is consumed, the diver simply pumps in more water to offset the increasing buoyancy. On the other hand, if they want to increase their buoyancy, they just purge some of the water from the tank.
Along with its other selling points, the Avelo System is claimed to let divers stay down longer, as some of their air supply isn't being diverted into a BCD. The absence of a BCD should also make them more streamlined, allowing them to move through the water with a bit less effort.
We're told that one charge of the battery should be good for seven to 10 dives by an experienced user, or three to four dives by someone who's still learning. Should the battery run out during a dive, there will reportedly be no immediate effect, although the diver will gradually become more buoyant – at a rate of about 1 lb (0.5 kg) every 15 to 20 minutes – as they consume the air in the tank.
Needless to say, the Avelo System isn't the type of thing that people should just buy and figure out on their own. For that reason, the Avelo company is now inviting interested parties to register for one of its training sessions in Maui, which will take place throughout next year. Commercial availability should follow in 2024 – pricing will be "competitive with standard scuba systems."
There's more information in the video below.
Source: Avelo
Agreed about Greg... :)
The web site says the tank fill pressure is 3,000 – 4,350 psi (206 - 300 bar). Let's assume the tank is filled to about the same pressure and volume as a typical aluminum 80 (10L) tank, 3000 PSI (206 bar). The web site also says no weights are necessary (with a wetsuit?? uh...) and that the system is "lightweight and buoyant when you enter the water." Okay, fine. It doesn't say how buoyant the system is, but, since it's not a metal tank, let's assume ~9 pounds (4 Kg), enough to let you float comfortably on the surface.
So the diver is buoyant and ready to dive. The diver then uses the pump system to push water into the tank, removing some of the buoyancy. How much? Well, at least 4 liters (4Kg) to gain neutral buoyancy. More if the diver's wetsuit is buoyant too. Let's say 5 liters (5 Kg, 11 lbs). That's a pretty common amount of weight to have on a weight belt for diving in temperate waters even with a negatively buoyant tank, depending on your gear and physiology. Now the diver is neutral. We good so far?
By removing 5 liters of gas volume from the tank, the diver has compressed the remaining gas to 5 liters (remember, we're assuming the same internal volume as a 10L tank) . The internal pressure has now doubled to 6000 PSI (412 bar). Your typical SPG is now pegged or broken. The regulator first stage is far beyond its working pressure has probably exploded.
But no problem! Let's assume the dive goes well, up until the diver runs out of air because his/her SPG was no longer working. OOA. Yikes! The panicking diver now wants to ascend by dumping water from the tank. But tank pressure is zero (ambient, relative to the water depth) and must power up instead of doing a buoyant ascent.
This can all be okay, if everything goes right, but let's not think about what the diver's buddy would do to make an unconscious diver buoyant if they don't have any ditchable weight. Or if the purge valve fails. Or if kelp clogs the inlet tube. Or if the battery goes dead.
I dunno man. Seems like too many failure modes, and a lot of marketing gimmicks. If they really want to convince divers like myself, their FAQ needs to address the questions I've posed above.