Review Diving the Avelo System

[EdMcNeill09]

Avelo will be at Scuba Show in LA June 1 & 2. If you're in the area you can go meet the CEO/Inventor Aviad. I'm sure our Course Director Jay will also be there. You can check out the gear and I understand pricing for Avelo Systems will be announced.

In other news Shearwater will be releasing the Avelo Mode for all its AI computers over the next year. First up will be the Teric. That will happen in the next couple of months. The Avelo Mode shows you the percentage of remaining gas available. It's pretty cool. I saw a beta version of this on Maui. I love this as someone who leads charters. I can tell my divers to be on the line with XX% gas remaining and not have to worry about how many times they may have run the pump.

 

[EdMcNeill09]

From what I can tell, failures would pretty benign.

You use the pump when you're getting light (approx +1 lb) and don't want to breath a little shallow any longer. If the pump fails, you'd swim up (while being a little light). Thicker wetsuit could have an issue as it expands (*), but shallow breathing with a bit of finning down would make for a safe ascent. Honestly, I suspect even without finning it will be slower than many normal OW diver ascents (where the BC expansion outpaces their reactions).

The purge (ballast removal) is non-electrical, with water being pushed out by the air bladder. One cannot take on much ballast in the first place, so if the purge failed open at the worst time (end of the dive at reserve pressure, losing all your ballast), you could be up to +9 lb buoyant. Finning downward can overcome that.

If the purge could not be opened for whatever reason, you might be around -1 lb negatively buoyant (you'd put in around 2 lb when getting light). Easily swimmable and you have to climb the ladder with that ballast (similar to a normal rig where you climb with your lead).

What is not obvious to me is if the pump continues to pump: I would hope there is an overpressure facility of some sort for the water release valve (similar to an OPV on a BC). We know there would be one on the air valve, but it would suck if the continued pumping would take up more and more of the tank volume, compressing the breathing gas beyond the capability of the burst disk. However, I suspect the pump would not be capable of pumping to such pressure. So you might be a few lbs negative, again swimmable.

(*) Avelo claims you don't have to worry about wetsuit expansion/compression. I don't believe this, as there is objective evidence of a 30% surface buoyancy loss at 33 ft (10 m). I've measured an XXL 7mm Bare Reactive suit at 16 lb of surface buoyancy, so that's at least 5 lbs that will be regained (obviously more from deeper). [Bardy, Erik; Mollendorf, Joseph; Pendergast, David (October 21, 2005). "Thermal conductivity and compressive strain of foam neoprene insulation under hydrostatic pressure". Journal of Physics D: Applied Physics. 38 (20): 3832–3840.]

In the case of a continuously running pump the greater risk is exceeding the 300 bar limitation of our regs. Uncontrollable free flow can result if this happens. We train divers to handle excess water in the tank by swimming in a slightly heads up position as they move towards ending their dive. In the real world, if this happened to me I would simply crack open the purge valve a bit as needed to bleed off the excess pressure. The pump will drain the battery eventually and stop running.

 

[scubadada]

During the Avelo Certification Dives we train for 2 possible failures: a continuously running pump and a failed dump valve. In the first case we have the diver simulate a continuously running pump by running the pump twice thus adding an additional 4lbs of water to the tank. In the second we have the diver vent all of the water from the tank. Both scenarios result in about a 4lb change in buoyancy. Not a lot. This requires the diver to swim in a slightly head down or up position as they work their way back to their exit point and end the dive. During our certification dives we swim for 30 seconds under these conditions before ending the skill and adjusting our systems to get back to neutral.

I described the 2 failure modes and the associated skills from the second RAD certification dive in the initial post of the thread.

 

[gordonscuba]

I had the opportunity to get certified on avelo recently. Normally, for either recreational or technical dives, I use a DIR / Hogarthian configuration because I find that most comfortable and the reasoning behind it makes a lot of sense. So, my usual rig for single-tank recreational level diving is a minimalist single-piece webbing harness, stainless steel backplate + STA, Apeks MTX-RC regulators, and no extra lead weight at all. I usually dive in warm tropical water with no wetsuit, or neutrally buoyant sharkskin and my buoyancy control is excellent. One of the things I like about the Hogarthian setup is that it is minimalist, hence in particular, it has eliminated any unnecessary source of drag so that the frog kick propels the diver efficiently (when in perfect trim). In principle I'd always like to remove anything unnecessary from my rig, but everything still there now is necessary. Naturally, I was intrigued by the idea of removing the wing, because in a minimalist configuration, the wing is the largest remaining source of drag. (I know that it's possible to dive a single tank with no buoyancy compensator as in the early days of scuba, but that involves starting the dive negative and kicking during most of the dive, so let's put that aside for now). If you want to be neutral all through the dive, something must compensate for the change in buoyancy due to breathing the tank contents, so removing the wing implies a tradeoff for something else that can do the wing's job. I hypothesize that the battery/pump combo might present less surface area and hence, less drag than a typical single-tank wing (even a mostly empty wing). I also like the idea of replacing the heavy steel backplate with a much lighter one, while still not requiring any lead weights, which is what happened. Hence, the system overall is less mass, which should imply less energy burned moving it through the water by F = ma. Less mass and less surface area. It doesn't really add any serious points of failure, because with the avelo system it's physically impossible to get too far off neutral buoyancy, so if the pump fails during the dive it's just a minor annoyance. You aren't actually dependent on the pump for safety. If I were going to dive avelo often, I would definitely replace their harness with the usual kind of DIR harness I made for my other backplates, based on a single piece of webbing, and of course continue to use my usual regulators with a long hose primary + backup regulator on a necklace.

 

[John C. Ratliff]

Well, it’s taken me a few days to read through this whole thread, but I don’t have one answer that I really would like to have. That is how is the HP cylinder hydrostatically tested? How does it come out from the other cylinder? That question was asked early in this thread, but never addressed.

SeaRat

 

[inquis]

how is the HP cylinder hydrostatically tested?

It's a single, carbon-fiber wrapped AL cylinder, with a flexible barrier between air and ballast water. My speculation is the barrier can be easily removed before hydro. Also presumably, the purge valve can be locked closed to achieve the higher test pressure.

 

[EdMcNeill09]

Well, it’s taken me a few days to read through this whole thread, but I don’t have one answer that I really would like to have. That is how is the HP cylinder hydrostatically tested? How does it come out from the other cylinder? That question was asked early in this thread, but never addressed.

SeaRat

Hydros are done at any testing center that currently does Hydros. Because there are openings on both top and bottom of the tank there are some different protocols that are provided to the Testing Center by Avelo. Before the Hydro the bladder is removed. This leaves the Testing center with a COPV (Carbon Fiber Over wrapped Pressure Vessel) similar to those used by the Fire Department. The thin walled Aluminum vessel is not removed from the Carbon Fiber. They are tested as a unit. The gas bladder is removed and a new one installed after the testing is completed. I hope this answers your question.

VIPs are performed annually by an Avelo Technician who is also certified to do VIPs. At this time the gas bladder is removed. The COPV is inspected and a new gas bladder is installed.

 

[lowwall]

Hydros are done at any testing center that currently does Hydros. Because there are openings on both top and bottom of the tank there are some different protocols that are provided to the Testing Center by Avelo. Before the Hydro the bladder is removed. This leaves the Testing center with a COPV (Carbon Fiber Over wrapped Pressure Vessel) similar to those used by the Fire Department. The thin walled Aluminum vessel is not removed from the Carbon Fiber. They are tested as a unit. The gas bladder is removed and a new one installed after the testing is completed. I hope this answers your question.

VIPs are performed annually by an Avelo Technician who is also certified to do VIPs. At this time the gas bladder is removed. The COPV is inspected and a new gas bladder is installed.

Thanks. Do they have a price yet for VIPs or the bladder?

 

[EdMcNeill09]

Thanks. Do they have a price yet for VIPs or the bladder?

Not yet. I imagine pricing for VIPs will be a little higher than for a standard tank as it will likely include the bladder. And honestly removing and replacing the bladder is a serious pain. This was the hardest part of doing the Avelo Technician Training. Perhaps it will become easier in the next generation of tanks. One lives in hope.

 

[John C. Ratliff]

Hydros are done at any testing center that currently does Hydros. Because there are openings on both top and bottom of the tank there are some different protocols that are provided to the Testing Center by Avelo. Before the Hydro the bladder is removed. This leaves the Testing center with a COPV (Carbon Fiber Over wrapped Pressure Vessel) similar to those used by the Fire Department. The thin walled Aluminum vessel is not removed from the Carbon Fiber. They are tested as a unit. The gas bladder is removed and a new one installed after the testing is completed. I hope this answers your question.

VIPs are performed annually by an Avelo Technician who is also certified to do VIPs. At this time the gas bladder is removed. The COPV is inspected and a new gas bladder is installed.

Now I’m really confused. So the inside cylinder is not the pressure cylinder, but a thin-walled aluminum vessel inside, which is not removed. But the valve appears from your diagrams to fill this thin-walled aluminum cylinder? How does the air get into the main cylinder when it is introduced into the thin-walled aluminum cylinder? Also, Inquest mentioned above in a different post that the purge valve can be closed to achieve the higher pressure. This unit, if I remember correctly, is rated at about 4,000 psi; does this mean that the hydro pressure will be 4/3s of 4,000 psi, or a test pressure of about 5300 psi? (That is from memory, and may be incorrect.).

SeaRat