rEvo III
Diving a rEvo is the easy option for me on day one of the International Rebreather Event. As a rEvo owner I know how to set it up and dive it, so borrowing one from Orca Safaga’s stock keeps things simple while the event it is organising settles down.
It also saves me having to wear a weightbelt. A rEvo is quite light out of the water, but its compact stainless-steel casing makes it very negative when immersed. Even Paul Raymaekers, its creator, uses only 2kg as a trim-weight with his drysuit. Everyone else at the event is diving in wetsuits.
Thomas, an experienced APD Inspiration diver, is preparing for his first rEvo dive. Like me, he is wearing a 7mm wetsuit. “John, tell Thomas he doesn’t need any weight,” says Paul.
“Thomas, you will be nicely neutral without any weight,” I say obediently.
I don’t want to say too much, because I don’t want to bias Thomas’s feedback.
After the dive, I ask him about the experience. “I was surprised that I didn’t need any weight,” he says. “My previous experience helped, but the rEvo is very easy to handle. It felt natural and nicely trimmed in the water.
“With the counterlungs in the box behind me, my front was uncluttered and head movement unrestricted.”
A unique feature is the dual scrubber. While other rebreathers have a single tube down the middle for the scrubber, the rEvo has a flat ovoid lid concealing two stubby half-scrubbers.
“It’s all very logical and simple, just one nut to remove the lid, the scrubbers, access the cells and the inside of the counterlungs,” says Thomas. “The dual scrubbers keep the profile low and make a lot of commercial sense.”
He is referring to the extended overall use of scrubber material if just one of the scrubbers is changed when an appropriate time has elapsed.
Another unique feature is a slide-down backplate extender. “This took the weight off my back and onto my buttocks, making it very comfortable.”
The basic rEvo is an MCCR with PO2 shown on the rEvodream, a combined O2 monitor and HUD. Additionally, most owners fit an optional Shearwater ECCR controller.
“The HUD slightly obstructed my nose when I wanted to clear my ears, but that could be moved. The Shearwater was clear and intuitive,” says Thomas.
Unlike other rebreathers at the Orca event, the rEvo has no BOV or octopus connected to the on-board diluent, so divers have to carry separate bail-out.
“The narrow casing brought the side-mount in close, and I am convinced that a rEvo would be easier to use inside wrecks, but it also got in the way of the diluent add valve,” says Thomas, referring to the MAV for diluent and O2 located at the bottom of the casing behind the diver.
I had not found it a problem, but there is a solution anyway: “I would want the over-the-shoulder MAV option Paul has on his unit.”
Thilo, also trying a rEvo for the first time, offers broadly similar comments, adding “for an easy shallow reef dive I would have preferred an octopus, and to leave the stage on the boat”. I notice that another diver at the event has already made such an addition to his own rEvo.
The rEvo addresses many issues by lateral thinking and alternative engineering. It’s like Marmite; divers either love it or hate it.

Poseidon Discovery/Cis-Lunar Mk VI
Day two, and I have been quick to get my name to the top of the list to dive the Discovery, Poseidon’s recreational rebreather. It nearly doesn’t happen; Poseidon’s shipment of pre-packed disposable scrubbers had been held up in customs and had only been cleared
late the previous evening.
The Discovery doesn’t come with a harness, though Poseidon does make one that marketing team and instructors Sverker and Marcus are using with their units. They tell me that the Discovery can be used with any BC. Is that a challenge I somewhat stupidly give them my scruffy old travel BC to fit.
The consequence is that everything rides up, and I spend my first dive struggling against hanging between the over-shoulder counterlungs.
Sverker comments that I looked perfectly in control in the water, but it doesn’t feel right.
Keeping my own BC on the Discovery, we spend time between dives adjusting the fit and trim-weights. With a total of 11kg, 6kg of which is in trim-pouches, my second dive is much better, but it is only a couple of days later, when I try Sverker’s Discovery fitted with the Poseidon harness, that I feel really comfortable. With this sorted out, it is a beautiful rebreather to use.
Neil was at last year’s rebreather event but unable to try the Discovery because of technical problems. This year he has a positive experience. “It breathes very smoothly and quietly, even compared to other CCRs, and balances easily at any angle in the water,” he says.
While other rebreathers use voting and averaging between three cells to monitor PO2, the Discovery uses dynamic calibration and validation throughout the dive, with one cell used to monitor the PO2 and a second cell checking up on the first.
“The sound of the regular calibration was distinctive and reassuring,” says Neil. “The PO2 was stable on the display and easy to read, as was all the other information, though it did feel like a paddle on my arm. I suppose that’s the price you pay for such clarity.”
The setpoint is automatically adjusted from 0.4 to 1.2 in small increments, rather than the single step that other rebreathers make.
“The change was smooth and without buoyancy blips,” says Neil. It’s an experience similar to my own, though I find it a bit aggressive at about 10m.
While half of the divers at Orca’s rebreather event are there to do 100m-plus dives on their own rebreathers, the other half, including me, are most of the time simply enjoying diving and photographing without bubbles in the normal sport-diving range.
The no-decompression limitation of the Discovery matches these parameters well, and the controller gives a warning when we push the limits.
Both Neil and I receive warnings to ascend a little because of insufficient bail-out for depth during second dives when our diluent is half-full.
“The buzz from the vibrating mouthpiece gave a clear warning,” says Neil. It is very effective, though I am disappointed with the HUD which, integrated tight to the top of the bail-out valve, I can’t see with my mask on.
I can’t help but feel that the Discovery is not quite finished. It has a very thorough self-test, but failures are shown as error codes that you need a cheat sheet to interpret (plain text error messages are a scheduled software revision).
It has pre-packed scrubbers, but the fittings to secure them are fiddly compared with the simplicity of other units. The exposed head looks a bit of a rat’s nest of hoses, especially once PADI’s required octopus is added to the diluent.

Submatix Quantum
I had enjoyed diving the previous Submatix rebreather, the SMS100, when it first came to the UK in 2006. Unfortunately it never had the distributor support necessary to become established as it has in other countries, particularly in eastern Europe.
The SMS100 is a fairly compact MCCR aimed at air and intermediate trimix diving, but the Quantum is built like a battleship, and designed to survive the harshest of extreme expeditions with many fallback levels of operation. There is space for up to six cells in the head!
It is in the final stages of development before being put through the CE process. On the bench, it is the biggest rebreather at the event. On my back, it is the heaviest.
The Quantum’s creator Matthias Lessmann has two units with him. Many divers want to try it, so I get only one dive with it.
The size makes it hard to guess just how much lead I will need. Off the back of the boat I make a buoyancy check and end up removing all but the 2kg of shoulder trim-weight and 4kg of keel-weight slotted into the backplate.
I could have done with removing another 1kg, but that would have meant more hassle than we had time for.
“It trimmed out well, though it pulled a little to the right from the separate BC feed cylinder,” says Thilo, who like me is having a go on all the rebreathers available. He is diving the MCCR version.
I haven’t noticed any pull to one side or the other on the ECCR I am diving.
It balances perfectly in a horizontal position, though the weight pendulums when I tilt to one side or the other to take photographs. It also tends to open the ADV when I roll to the right.
This may be desirable when hands are busy in a cave, but as a photographer I would tighten it.
I also suspect that the single large back-mounted counterlung traps and then releases pockets of gas, as I notice an occasional blip in the PO2 if I roll to the left. This is a glitch rather than an issue, because physiologically it all averages out. Buoyancy control is easy, even in shallow water.
Alexi, an SMS100 instructor, is also trying the Quantum for the first time. He dives the ECCR after me, drawing a comparison with the SMS100. “The OPV is a great improvement, much smoother, but the overall weight will not be good for travel,” is his assessment.
Neither trial unit is fitted with hose-weights. “Hose-weights would make it much more comfortable,” says Alexi.
“I have hose weights on my SMS100 at home.”
Thilo agrees, adding: “The mouthpiece was hard and pulled into my mouth – it needs to be softer.”
Swimming behind Alexi, I admire the transparent scrubber. The indicating scrubber material shows a purple band where CO2 is being absorbed. This is not a definitive measure of usage, but it is reassuring to see.
More importantly, I can also see that there is no water in the loop, and the outside of the scrubber is packed evenly.
While the colour display of the handset is easy to read under water, both Alexi and I think that some of the surface information is a bit small. Matthias explains that the next version of the software is already planned to correct this.
With distributor support, I can see the Quantum appealing to some UK divers.

APD Evolution Plus
Since APD kick-started the whole rebreather scene with the Inspiration in 1997, things have moved on considerably.
Other rebreathers are now available tested to EN14143 (the CE standard) and the standard itself is close to completing its first revision, but APD remains the market leader.
Martin Parker, who is in Safaga with service expert Tony Reid, tells me that the Evolution Plus is APD’s best-seller by a long way. They both have Evolution Plus rebreathers with them, and Orca has the full spread of APD rebreathers in its rental stock.
Initially, I am surprised that there is little demand for try-dives with APD. Even Thilo, who is having a go with everything else, hasn’t signed up. “Because I am doing the course next week,” he explains.
I then realise that the low demand is because nearly everyone at the rebreather event has already used an APD rebreather. I certainly have, though the last time was about four years ago. I am due for a refresher.
All Orca’s rental units are in use, so Martin arranges to borrow one from one of the APD staff ashore for the day so that I can dive with him and Tony.
My next surprise comes when I switch the unit on and the Vision handset comes up in German. Fortunately Tony services units set up for all sorts of languages, and scrolls through the menus to set it up for me.
Martin tells me that different language packs can be uploaded by users, and APD can generate a new one if needed. Anyone for Klingon
Considering APD’s worldwide market, I can understand why it does this and that others have yet to catch up.
Time to dive, and I don’t need to wonder about weight. I have 8kg written in my logbook from the last time I used an Evolution with the same wetsuit.
I get my next surprise when I find that the diluent is already on – and almost empty, having leaked out overnight.
The solution is simple. I pick up a spare side-mount of 32% nitrox with
a standard direct-feed hose and connect it to the diluent MAV on the left counterlung. Using the counterlungs for buoyancy control is not the most comfortable way to dive, but it works.
I couldn’t have done this trick with any of the other rebreathers in their off-the-shelf configuration, and I wouldn’t have done it on anything but a simple dive with an expert minder.
By my second dive I have found a decanting hose and topped up the diluent. Tony has also changed a cell that was over-reading and responding slowly. Teledyne has now left the diving market, so APD makes its own cells.
I find back-mounted counterlungs more convenient for photography. Nevertheless, I can work with the over-the-shoulder counterlungs, and there is something reassuring about the way the Evolution Plus breathes. It’s a bit like being cuddled by the rebreather through the dive.
Development of the range has been incremental, with new or revised features being retro-fittable to even the earliest units. Recent developments are a screw-topped battery-box and a BOV, which I note both breathes well and is nicely balanced in the water.
It is also the best mouthpiece for shouting into and actually being understood by your buddy!
Later in the week, Martin is testing software for a PADI recreational version. He tells me that he will soon have a stepped auto setpoint switch that is smoother in shallow water.
For the hardware, a modified scrubber that eliminates the spacer
and bypass O-ring is in development, to help avoid user-error when assembling the unit.

My final rebreather of the week is scheduled to be the JJ-CCR, guided by Dave Thompson who originally worked with APD to develop the Inspiration. Unfortunately, a tummy bug intervenes and Dave is unfit to dive.
So I can report only my observations, the comments of owners and Dave himself – as long as I don’t lure him too far away from the porcelain. It’s hardly unbiased, but it’s the best I can do. With the unit now CE-marked, DIVER hopes to bring you a full test soon.
First impressions of the JJ is that it looks very conventional – a robust aluminium tube for scrubber, sensors and plumbing; O2 and diluent cylinders to either side; and hoses to a mouthpiece. All this is controlled by a Shearwater controller, like the rEvo, but backed up by a Shearwater HUD.
On closer inspection, all this conventionality has been refined in the minutest detail. A single recessed button enables the head to be removed to change the scrubber or cells.
Counterlungs are over the shoulder, but with the majority of the lungs behind the diver’s back and manual add valves routed to the front.
A compact BOV comes as standard. Rails are built into the canister to fix cylinders with cam-bands. All this sits on a shaped stand of stainless steel rod.
The divers look comfortable and well-balanced in the water. Weightbelts vary between 0 and 4kg, depending on thickness of wetsuit and cylinders used.
Nearly all of them are using the JJ without modification, generally agreeing that there is nothing they would want to change – except for Sepp, who has added a small anode to protect against electrolytic corrosion, and an APD gas connect system for offboard diluent.

Auto Diluent Valve (ADV): Adds diluent to the loop when volume is low, usually engineered using a similar mechanism to a regulator second stage.
Bail-out Valve (BOV): Integrated rebreather mouthpiece and open-circuit regulator, allowing a diver to switch between the two without removing the mouthpiece.
CCR: Closed-circuit rebreather.
Counterlungs: Part of the loop that acts as a reservoir of gas as a diver breathes in and out.
Dive Surface Valve (DSV): Rebreather mouthpiece that does not incorporate a BOV.
Electronic CCR (ECCR): Oxygen is added by electronics opening a solenoid valve.
Head Up Display (HUD): Display in front of the diver’s eyes.
Loop: Part of the rebreather through which the diver’s exhaled breath is cycled while being scrubbed of CO2 and topped up with oxygen.
Manual Add Valve (MAV): Usually two valves for the diver to add diluent or oxygen manually to the breathing loop.
Manual CCR (MCCR): Oxygen is added by a constant trickle supplemented by the diver using the oxygen MAV.
Over-Pressure Valve (OPV): Allows gas to escape from the loop when the volume expands, typically on ascent.
PO2: Partial pressure of oxygen.
Scrubber: (a) Device for removing CO2 from the loop; (b) Chemical within the device that absorbs CO2.
Setpoint: Partial pressure of oxygen maintained in the loop.
GETTING THERE: John Liddiard flew from Gatwick to Hurghada with EasyJet, Ground transfers to Safaga take approximately 45 minutes.
DIVING & ACCOMMODATION: Orca Dive Club Safaga,
REBREATHERS: rEvo,; Poseidon,; Submatix;, APD;, JJ,
MONEY: Egyptian pound
PRICES: All Orca’s rebreathers can be rented for 180 euros per week plus consumables. A six-day 12-dive package costs 246 euros booked in advance. Accommodation in the Orca Village costs 20-32 euros a night depending on season.