WHEN APD BOSS Martin Parker sent me the recreational version of the Evolution closed-circuit rebreather (CCR) to try, he told me that I’d have to try to think like a novice diver. Not a problem for me – I’m a novice every time I go diving.
The question was, where would be a good place to use a CCR intended to go down to only 18m What would be the advantages of such equipment
The solution was to go somewhere that required a covert approach to diving. If you want to see a tiger, you hide up a tree and wait. If you want to see schooling hammerhead sharks, you need to hide somewhere under water and wait it out too.
The isolated seamount that is Cocos Island, 350 miles off the coast of Costa Rica, is a magnet for Eastern Pacific
sea-life. One can expect to see schooling hammerheads, Galapagos sharks, tiger sharks, mantas and mobulas and, hopefully, whale sharks during a visit.
It’s a place where whitetip reef sharks are as common as anthias are in the Red Sea, and large marble rays pile up in clusters on the seabed.
I set off for Cocos on board Undersea Hunter’s mv Sea Hunter, with Terry Fisher from APD. The vessel is a favourite with film-maker and CCR-user Howard Hall, and known for its sympathetic approach to rebreather divers’ needs, as its owners and many of the long-time crew are users themselves.
The operation was able to supply us on-site with the scrubber material and 2-litre cylinders we needed, so no air-transport problem for us. Not only that, but Avi and Yosi the owners invited me as their guest. It would have been churlish to turn them down!
Scubatours then sealed the deal by sponsoring my international flights.
An Evolution in its shipping crate without cylinders weighs in at 23kg at the airport check-in desk.
We took with us Evolution+ rebreathers in Rec 1 mode with the option to upgrade the software to Rec 2.
The Evolution+ has the small size of the Evolution, but with the bigger scrubber duration of the Inspiration.
One prerequisite of the PADI specification is that either you employ pre-filled scrubber cartridges or have your scrubber refilled each time by a suitably qualified person (ie, a PADI rebreather instructor). Well, that gave Terry something to do in the evenings while I sorted out my camera.

So what’s new Well, first of all, the three versions of the APD rebreather, the Inspiration, the Evolution and the Evolution+, are each available in Type R (Rec) specification.
The Inspiration has 3-litre cylinders and a 3-hour scrubber canister; the Evolution has 2-litre cylinders with a 2-hour scrubber canister; and the Evolution+ has the bigger scrubber combined with the smaller cylinders. Intelligent monitoring of the tempstick display can extend scrubber durations.
In Type R specification, each model comes with an open-circuit bail-out valve (BOV) integrated into the mouthpiece, an automatic diluent addition valve so that air is added to make up the loop volume as you go deeper, a tempstick that will monitor the progress of the active part of the scrubber as it passes through the stack, and automatic activation on contact with the water.
Refusing to give up the success with safety benefits of the tempstick, APD has decided against the prefilled scrubbers as used by Poseidon and has stuck with the industry-standard Sofnolime 797 and loose O-ring and spacer system familiar to standard APD rebreather users.
In addition, however, we had the benefit of the new built-in CO2 monitors, something that would have instantly revealed any possibility of having installed this loose O-ring incorrectly.
Because of the nature of our project, our rebreathers had every bell and whistle available to allow us to progress through all the levels of rebreather diving throughout our trip.
However, Type R units do not have a shut-off to the automatic diluent-addition valve (ADV) or a separate manual oxygen-addition control.
This is intended to minimise the risk of mistakes being made by the user. Nor is any non-manufacturer-approved addition allowed.
The point is that, should a diver wish to progress to Tec 60 and Tec 100 levels of certification, these can be added to an existing unit later.
Each unit comes with the Vision handset, which takes information from two separate oxygen controllers within the rebreather electronics head. This handset is operated using three large buttons, and you should turn it on before diving.
If you were to jump into the water without turning it on, the unit would provide life-support provided you opened the oxygen-cylinder valves, but would also sound a non-suppressible alarm and display “Dive Start Error” on the handset display. It would be a very foolish diver who did not ascend immediately and abort the dive.
In addition to the handset, a head-up display (HUD) is visible before your eyes. It would show red lights at this time. The HUD is operated from a set of LEDs in the electronic head, and the light is transmitted to it via a heavyweight fibre-optic cable – a very elegant engineering solution.
This HUD can be used to monitor the dive once you’re familiar with the code, but I find that two green lights (yellow at depth) are very comforting, whereas anything else means “look at the handset”. I’ve rarely seen a red light in all the time I’ve used Vision electronics.
In Rec 1 mode, the unit is intended for use to a maximum depth of 18m, with a visual alarm at 19m, although the audible alarm that you can’t turn off comes on only at 20m.
If you go deeper, ignoring this alarm, the unit continues to give deco information, but you should turn back.
We soon uploaded the software to change the units into Rec 2 mode. This allowed us to go as deep as 40m, and you don’t really need to go any deeper at Cocos. The audible and visual alarm comes on at 41m.
So with scrubber canister and oxygen and air diluent cylinders filled, and the units tested for leaks with both positive and negative pressure checks, we were ready to go diving.

Turning on the handset takes you through a series of automatic checks of the four CR123A lithium batteries, the tempstick and the three O2-sensing cells, combined with prompts to turn on both the cylinders, check the OC bail-out valve and the mouthpiece valves, and open the over-pressure valves on the counter-lungs.
It then tells you to open the mouthpiece (to the CCR setting), and automatically flushes the unit with neat oxygen and calibrates the cells. This takes a couple of minutes.
I lost one dive when I discovered thatmy diluent (air) cylinder had been inadequately filled, and Terry lost a dive to a temporary solitary cell connection error, but that wasn’t bad for a total of 17 consecutive dives.
The twin sets of batteries in their waterproof compartments are no longer sited within the air-space of the breathing loop, as they have been with earlier models.
There’s an integrated-weight system, and I tended to install my weight pouches once we had arrived at the dive-site after a somewhat bumpy high-speed ride in one of the Sea Hunter’s fast panga pick-up boats.
You can also stow lead high in pockets at the back of the wing if you so wish.

WE HAD UNITS WITH THE LATEST back-mounted counter-lungs, which gave us an uncluttered chest area and got rid of the “Mae West effect”. I noted that I had much more freedom to look around than with the front-mounted counter-lungs, and the hoses with their T-pieces were no longer intrusive.
The back-mounted counter-lungs come over the top of the shoulders, so that effective breathing resistance is virtually unnoticeable.
They are almost like front-mounted counter-lungs but reversed. However, they are of lower capacity, which may prove significant.
An over-pressure valve is mounted on each counter-lung. These have pull-dumps fitted, but whatever you may be told, they need a little feeling for should you need to use them. I found it more convenient to exhale expanding gas during an ascent through my nose.
On descent, it’s necessary to vent the loop through the nose, letting the ADV take up the slack on the first inhalation at depth. In this way a minimum amount of lead is required.
I used 8kg while wearing a 5mm suit, and I’m not known for my compactness.
Because the counter-lungs were a little small for me, I could feel the over-pressure valves belching as I descended, indicating that lung capacity was at its maximum. If at any time I took a deep breath, the ADV cut in.
I would have preferred a slightly bigger set of counter-lungs, and would then have used less diluent on each dive than I did.
You use a wing for buoyancy control. Things are different with closed- than with open-circuit in that your lung capacity does not affect your overall buoyancy from moment to moment. So it’s better to stay at a consistent depth and swim around obstructions than swim under or over them.
We were often in a led group of open-circuit divers without this restriction, which meant a lot of fiddling with the wing, adding and jettisoning air. This in turn was wasteful of the small supply of diluent.
I preferred dives such as the one on Alcyon, a seamount, where we went down and stayed there until it was time to come up again.
Decompression obligations are at a minimum, because the unit always gives you the ideal mix. However we
did get up to 10 minutes of ascent-time displayed on dives of around 35m deep.
This ascent time is quickly shed as one goes up, so that although one could say we were doing deco dives and staying at the bottom for much longer, we were usually back in the boat before the accompanying no-stop open-circuit divers had done their 5m safety stops.
I also monitored my dives on a stand-alone Suunto DX computer that tied in nicely with the deco information given by the Vision electronics.
I merely needed to do an additional brief deep-stop at 18-16m to satisfy the DX. I got to 38% recorded oxygen toxicity units each day.
The rebreather was set to give a consistent partial pressure of oxygen of 1.3 bar once we were deeper than 20m.
At a constant PO2, as you go deeper the O2 in the breathing loop represents a smaller percentage of the total gas mixture. Conversely, as you near the surface at the end of the dive the O2 percentage increases, which can lead to buoyancy control problems and a waste of O2 if you use too high an O2 setpoint.
On the other hand, it would be quite impossible to maintain a PO2 of more than 1 bar when the ambient pressure is less, so you start off with 70% (PO2 0.7bar) at the surface.

OLDER APD CCR UNITS operate with a hard set-point change. You start off at PO2 of 0.7bar and change to 1.3bar at depth, changing back to 0.7bar on the way up when you reach the shallows.
This can mean that quite a lot of oxygen is added on the way up, at a time when you need to vent off gas to control your buoyancy.
These latest recreational units use a sliding system that gradually moves from 0.7bar pO2 to 1.3bar, so buoyancy changes are almost imperceptible, thereby doing away with another skill formerly needed by CCR divers.
The Vision electronics take care of the deco requirements, although for recreational dives I saw 999 minutes of no-stop time displayed for most of the time.
When I got to within a couple of metres of the surface I got into the habit of switching the BOV at the mouthpiece to open-circuit mode, and breathed diluent just as one would with traditional scuba. This also ensured that I had the mouthpiece closed when it was time to climb out of the water.
Both Terry and I found that we used around 150 litres of oxygen per dive (75bar from 2 litres), including the gas needed to calibrate the cells each time.
The mouthpiece with the BOV combined is quite a big lump, and I could have done with a longer one to bring my back teeth into play to grip it.
In the ripping currents of Cocos, there were times when I felt I needed to hold onto it with a spare hand, just to give my forward teeth a rest. I wished I had taken the optional mouthpiece strap.

Potential customers need to know how this APD recreational rebreather compares with the Poseidon Discovery Mk6, at the time of writing the only other recreational CCR on the market.
Well, both meet all the PADI prerequisites, and the Evolution is of a similar size. The mouthpiece of the Poseidon is easy to switch to OC and the electronics know that you have done that, whereas the APD mouthpiece is slightly harder to get to grips with.
The Poseidon uses two constantly recalibrated cells and a rechargeable battery-pack, compared to APD’s two primary-cell battery-packs, one for each oxygen controller.
On the Poseidon, one cell controls the unit while the other acts as a continual check on the first. It only gives you a red light (and vibrating mouthpiece), at which point you are expected to bail out to OC and ascend, aborting the dive, whereas the APD is reinforced with an audible alarm and gives a little more information – although you should do the same thing and abort the dive.
This uses two out of the three cells’ outputs at any one time, with voting logic to choose the most accurate.
The Poseidon automatically checks a large number of aspects, but should there be a problem one needs to refer to a key to decipher the display. The APD unit is simpler in this respect. Any fault is identified in easily understood words on the handset display.
The other difference is that the APD is modular and so easily upgraded should the user wish to progress.
The Poseidon was intended to be used only with pre-filled scrubber cartridges, but this has been undermined by people filling their own when proprietary replacement cartridges are not available.
The APD unit appears to be more robustly made, and the company has a long track record of continual development in its field.
With both models, in Rec 2 mode it is intended that divers carry an additional separate side-slung cylinder for off-board OC bail-out should it be required.
The prospective buyer should examine both units and make an informed choice.
The most crucial thing to realise is that, should you get a red light/warning with either unit, you must switch to OC bail-out and abort the dive. This mindset and discipline will save your life.
Price Complete with BC and tanks, almost identical. The Poseidon Discovery V1 costs £5800, while the APD Evolution/ Evolution+/ Inspiration costs £5840. Upgrades to the APD CCRs cost £117 to use technical nitrox and £235 for trimix.
How was the CCR when it came to getting close to big animals I’d hide behind a rock and ambush passing sharks with my camera. This always worked unless another diver equipped with traditional scuba came to join me, blowing bubbles, making a load of noise and scaring the animals away.
To get success you need to be on a rebreather-only expedition or be allowed to dive alone.
My ultimate judgment of the hardware I want one!

APD rebreathers, www.apdiving.com. John Bantin travelled at the invitation of Scubatours Worldwide (www.scubascuba.com) and stayed aboard Sea Hunter, courtesy of Undersea Hunter (www.underseahunter.com).