At the first sight, rebreather construction doesn't look complex at all. Probably because of this almost every day new rebreather designs are created, made and fail. Reality shows that the devil is in the detail and construction of really good rebreather, meeting the standards and demands is not easy. 

How then the rebreather comes into existence? First comes the design which - with little luck, enormous perseverance and considerable financial outlay - turns into final product. This product should be then tested in real conditions. The manufacturers use for that the services of trusted bunch of experienced divers, who dive with prototype units and give back their observations, data and informations. Based on the collected data, the design is improved or changed and all starts again. It is expensive and time-consuming process. If the designer had the opportunity to check the effects of his work on site, in his own office - that would be an ideal situation. That would give huge possibilities of development and a chance to create well designed and - what is most important - proven in reality rebreather. 

Such possibility exists and rEvo makes use of it. The rEvo manufacturer, as one of the few in the world, owns the ANSTI unit. ANSTI is a device that combines hiperbaric chamber and arificial lung and can monitor and analize breathing parameters. Thanks to ANSTI, rEvo manufacturer can "dive" many times a day in his office, simulating 99% of diving conditions, including pressure, temperature, breathing cycle, gas humidity, and CO2 retention. That priceless opportunity allowed to create the rebreather nuanced to perfection in every inch, at relatively low cost.

The rEvo story

The first rEvo was built in 2006 and it was mCCR. Just one year later manufacturer made significant changes in the construction and introduced version II and after next 2 years, in 2009, the first model of rEvo III was made. rEvo III is produced till present day. In 2014 rEvo 2014X (Expedition) had its debut. rEvo 2014X (Expedition) is complete, lightweight, titan rEvo III hCCR with rMS system and all necessary options.

rEvo I: 2006
rEvo II: 2007
rEvo III: 2009
rEvo III X (Expedition): 2014

rEvo III

mCCR + eCCR = hCCR

In general, due to the way of oxygen addition, we can divide rebreathers into 2 types: mCCR i eCCR.
mCCR - manual or mechanical rebreathers - are based on the fundamental principle of close circuit diving: human metabolizm consumes a fixed amount of oxygen (at constant effort) and it's about 1 liter per minute. A diver with 3l tank filled with oxygen at 200 bar can - in theory - spend 10 hours under water. In fact oxygen is "wasted" during ascend and some other procedures but all in all we use it very little. Furthermore, the depth does not affect the oxygen consumption. So all we need is the system providing fixed amount of oxygen to the breathing loop, exactly as much as is metabolized. CMF (Constant Mass Flow) is such a system, providing fixed oxygen flow to the loop by constant flow orifice. In ideal conditions (during relaxed swimming) the amount of oxygen provided by CMF is the same as amount metabolized by the diver, which ensures fixed amount of oxygen in the breathing loop. At higher effort and during ascend the diver has to add more oxygen to the loop, using manual inlation valve, to keep its required amount. The advantages of mCCR are simple construction and relatively small quantity of possible failure sources. These units don't have computers, electrovalves and other elements susceptible to failure. It's just an orifice (a hole of microscopic diameter) providing oxygen to the system regardless of the other elements. Drawback of this sollution is the need for constant monitoring of ppO2 and manual "refilling" it to the setpoint, what - in stressfull situation and during ascend - significantly increases the risk of hypoxia (too small amount of oxygen).

eCCR - electronic CCR - is a system equipped with solenoid, an electrovalve which opens on demand, adding oxygen to the breathing loop. Electronic rebreathers are controlled by computer connected to oxygen sensors, using special algorythm to maintain oxygen setpoint in the breathing gas. Let's say that we want, during all the dive, to breath the gas with oxygen partial pressure at 1.3 bar - that's what we call setpoint. After correct setup the computer is monitoring ppO2 and in case opens the solenoid to add oxygen in an amount providing ppO2 of 1.3 bar. The advantage of this system is convenience - the diver doesn't have to manually maintain fixed ppO2 in the breathing loop - the computer does it for him. The drawback is higher possibility of critical failure - for example solenoid blocked in open possition or electronic failure.

What is the hCCR?

Why not use in the same time the advantages of mCCR and eCCR while minimizing their drawbacks? hCCR - hybrid CCR - is such solution. rEvo is the first rebreather in the world which is mCCR and eCCR at the same time. Constant flow orifice adds oxygen to the breathing loop all the time. There is manual oxygen inflation valve of course but  we also have the solenoid, controlled by the computer, which opens to maintain the setpoint when ppO2 drops below the setpoint. What this solution gives us?

How to use hCCR efectively?

It's very simple - diving with rEvo we setup its eCCR part (Shearewater electronics) for setpoint of 1.20 - 1.25 bar and then "manually" maintain required ppO2 in the breathing loop at 1.3 bar. During normal, stresless dive the constant flow orifice adds the same amount of oxygen as metabolized by the diver. In that way, ppO2 once set manually (at 1.3 bar for example) stays constant so the solenoid doesn't work at all. In stresfull situation or when diver's effort rises or during ascend, ppO2 drops below 1.25 bar (oxygen loss is higher than its constant in-flow) so the solenoid opens to stop further ppO2 drop. This solution minimizes the possibility of solenoid blockage (because it doesn't work almost at all) without sacrificing the comfort of being protected by the computer watching the oxygen partial pressure not to drop below safe level.

 ELECTRONICS

rEvo uses Shearwater Petrel as a handset, decompression computer and rMS System computer. Readable, LED display provides all necessary information in clear, very intuitive way. Petrel receives information about oxygen cocentration in the breathing loop from 3 independent sensors. At this base it calculates non-decompression time and - after exceeding this limit - mandatory decompression schedule, using ZHL-16C algorythm (VPM upgrade is avilable as an option). In addition, the computer offers the possibility to switch between CCR and OC mode underwater, what makes it an ideal solution to calculate decompression for bailout. 

Depending on whether rEvo is equipped with rMS System or not, Petrel can be also solenoid controller (Petrel Hardwired) or just an interface between diver and rMS System (in that case separate rMS computer controls the solenoid). 

NERD (Near Eye Remote Display) is a modern display system providing all necessary information. Using special lens system, NERD displays diver accurate projection of display of the Petrel mounted on the breathing loop. This solution enables constant monitoring of inormation displayed by the computer, without "taking a look" to the wrist - you only need to accomodate the eye on the closest point. During "normal" watching the world around you the NERD seems to be "invisible" and doesn't disturb the field of view in any way. This solution is ideal for photographers, who have both hands full and do not want to give up the possibility of constant monitoring of ppO2 and other dive parameters. In addition, NERD increases comfort by elimination of the wires wrapped around diver's arms.

rEvodream is another noteworthy element. Technical divers know the concept of redundancy very well. According to good diving practices, every element which is essential for diver's life should be doubled (redundant). The key rebreather element is the electronic module, informing diver about oxygen content in breathing gas. Most rebreathers have two independent electronic modules, however in most cases they get the information about ppO2 from one set of oxygen sensors.

rEvo made one step forward. The main computer, informing about oxygen content in breathing loop, calculating no-decompresion time and mandatory decompresion is Shereawater Petrel. Exceptionally readable, equipped with dual power supply and connected to 3 oxygen sensors. But it's still not enough. Every rEvo can be equipped with additional electronic module: rEvodream. rEvodream has own power supply, independent wires and oxygen sensor (or even 2 sensors for 1 rEvodream). Thanks to such sollution it's completely independent, separated from any other electronic systems module that informs the diver about oxygen content in the brething loop. rEvo can be equipped with 2 rEvodreams. In such configuration the unit has 3 independent (own power supply, wires and oxygen sensors) electronic systems, what means that even if one of them fails during the dive, we still have 2 (redundant!!!) working electronic systems. rEvo is the only rebreather on the market offering 5 oxygen sensors connected to 3 independent measuring systems.