A Comparison-contrast Of Available Rebreathers

[almitywife]

in reference to this original thread; http://www.scubaboard.com/forums/rebreathers/210392-comparison-contrast-available-rebreathers.html

Gill Envy, ScubaBoard - View Profile: Gill Envy, has spent alot of hours in formatting this very infomative article on current rebreathers and options

many thanks


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Part I
Introduction

As promised I have gone through and made some corrections and suggested additions. I have diverged from my original intent of having a relatively short synopsis in order to be more comprehensive.

Understanding what the various rebreathers have to offer is a formidable challenge and there are practically as many varying opinions out there as there are rebreather divers. I remember how mind boggling it was when I first started out trying to make sense of it all, and how frustrating it was to ask for opinions of which rig is the best, only to be given some nebulous one line answer like, “it depends on what you want to do” or being given what amounted to a sales pitch from a distributor or instructor who has a stake in promoting one type over another. Getting an objective answer is nearly impossible so it’s best to get as wide a variety of opinions as you can. While I respect the opinions of manufacturers, retailers and instructors, I thought it might be helpful to put something together that was from the perspective of a diver who has no commercial interest to protect or promote and is not beholden to any certifying agency or manufacturer. Some of this write up is fact and some is just my personal observation and opinion.

The bad news is that the answer to “which unit should I buy?” does ultimately depend on what your needs and preferences are, and ultimately you are the only one that can determine that. Now that I am a couple of years into the journey, I have attempted to go back and explain some of the basic differences as I now understand them in hopes that it might be helpful to others just getting started. The good news is that there are a lot of wonderful choices out there. It’s an exciting time to be getting into rebreathers as the industry seems to be hitting a critical mass where many solid options are available. I would recommend gathering information from as wide a variety of sources as is practical for you to determine for yourself what would best suite your needs before taking the final plunge. My hope is not to impart “the truth” but rather to leave you with helpful questions and perspectives that will help you on your quest to develop your own understanding of your priorities and needs. While I started out in pursuit of the one perfect unit, I have begun to respect them all for their own unique qualities.

To give you some idea of my background, to date I have 130 hours of CCR diving under my belt, my wife and I have owned and are mod 1 certified on an eCCR and a mCCR, the Evolution and now the Shearwater Copis Meg (about 230 combined CCR hours between us). We enjoy both tropical and cold water dry suit diving. I have trained to the dive master level and done over 700 dives since getting my original C-card 13 years ago. That said, I by no means wish to promote myself as an authority on the subject of rebreathers and, try as I might to be objective, I have my own evolving experiences, opinions and bias, which I am choosing to express openly. I encourage anyone to post variations in opinion or corrections. The feedback has been very helpful so far, thanks to all who have helped on this “little” project. I’ve done my best to incorporate new information and update my original, somewhat sloppy post.

Before diving in to the individual makes and models, I’d like to go into some general background on current rebreathers and trends that I am aware of.

There are two main differences between available CCR's. There are eCCR’s and mCCR’s. ECCR's rely on an automatic computerized set point controller with a solenoid (an electronically controlled piston valve) to help monitor and maintain o2 balance automatically by injecting o2 into the loop as needed. MCCR’s require manual o2 injection, assisted by a constant mass flow orifice. Near continuous vigilance is required for the safe operation of both types. In general, the design of mCCR’s and eCCR’s appear to be aiming at a similar goal, balancing safety and convenience, they just go about solving some of the main challenges in very different ways. Many deep dives are being done successfully on both mCCR and eCCR’s, so the choice between the two major styles is no longer thought of as a matter of depth; it ultimately comes down to a matter of personal preferences and priorities…there are merits to both.

Research and Design of each rebreather manufacturer is currently governed by a wide variety of individual manufacturing standards (often not available to the public) and even in some cases governmental standards such as CE certification. Unfortunately there is not much agreement on basic standards.

One of the challenges that CCR’s address in different ways is that while oxygen consumption ebbs and flows with changes in metabolism, the basic metabolic tolerances for o2 on a cellular/molecular level do not change with depth, while on the other hand the loop volume and gas density changes dramatically with depth. Keeping po2 relatively constant while gas volume and density in the loop change throughout the dive is key to enjoying the decompression benefits of a rebreather as well as staying within life sustaining o2 limits. Essentially, a rebreather is a nitrox blender on your back, optimizing the gas mix to match the ideal ratio of o2 and nitrogen for changing depths throughout a dive. The ideal threshold for o2 on a cellular level is measured in partial pressure of oxygen (po2). Too much o2 or too little can both be just as deadly.

 

[almitywife]

part II

Automatic Injection Rebreathers:

ECCR’s address the need for constant po2 by employing an electronic set point controller, a po2 monitoring system that generally requires three o2 cells. O2 cells are notoriously unstable so 3 cells are typically used in eCCR’s where the computer employs an automatic voting logic; the set point controller automatically goes with the two closest readings. While the user is expected to monitor proper function, staying mentally engaged on an automated process has its challenges. The set point controller uses the readings from the o2 cells to drive a solenoid to inject an exacting amount of o2 to maintain constant po2 throughout the dive. Because eCCR’s are able to monitor and maintain a set point, pressure-compensating first stage regulators are used, I get into the reasoning later but this gives them a deeper depth potential in their stock configuration than most mCCR’s in their typical stock configuration.

The firm believers in eCCR's like the convenience of a set point controller, and often believe that it is a “safety net” in case of getting overly task-loaded or distracted. Some even going so far as to run their eCCR’s manually, relying only on the set point controller minimally…however, the injection rate required to do this is significantly higher than on an mCCR because there is no assist from a constant mass flow valve. ECCR's seem particularly attractive to photographers, deep penetration wreck divers and cave divers, those for whom hands free function is a high priority.

Critics of automatic systems refer to them as something more akin to a “safety blanket” which can all too easily encourage dependence and charge that they encourage complacency, leaving the diver vulnerable to the possibility of being “checked out” in that rare but possible moment that they stop functioning properly. For reasons yet to be determined, there are many fatalities associated with eCCR's and this has lead many people to fear rebreathers of all kinds. The trends in eCCR development have been to overcome the apparent added dangers of complexity and dependence by providing ever more sophisticated warning systems to alert the diver before a problem becomes critical. It appears to me that significant strides in this direction are being made.

The drive for solid research into fatalities is growing. Until recently, the efforts to find answers has been hindered by an apparent resistance within the CCR diving community to take a cold hard look at the numbers and create a standard for gathering objective data. The wishes of the families of deceased CCR divers and the closed-book stance of manufacturers to reveal total units produced and causes of fatalities they research have all contributed to an inadequate database for conclusive and objective study…thankfully this is beginning to change. Now that rebreathers are becoming more popular, DAN, with the help of many generous folks, is starting to work on a database and look more squarely at the cause of CCR fatalities to help make improvements in training and manufacturing standards.

 

[almitywife]

Part III

Manual Injection Rebreathers:

When I first got into rebreathers, it seemed like manual injection rebreathers were yesterday’s news…obsolete, unsophisticated and just not cool. At that point eCCR’s looked like the ultimate way to go. Two years later, it seems like quite a few people, myself included, are discovering just how valid and sophisticated an option mCCR’s actually are. There seems to be a surge in interest in manual systems and recently the number of available units has expanded exponentially. For these reasons I will go into considerable detail about them and why I think this trend is occurring.

“Manual” vs. “electronic” only refers to the o2 injection, as both eCCR’s and mCCR’s are becoming more and more electronically advanced. In-line deco, a HUD (heads up display) and ever more sophisticated and user-friendly computer monitoring systems are being added to each.

Even with the trend toward greater complexity, manual systems continue to adhere, with near religious conviction, to leaving out the solenoid/automatic set point controller. To lessen the need for frequent manual injection, a constant mass flow orifice is used to administer a continuous flow of o2 molecules into the loop at a rate that is tuned to just below the diver’s average metabolic rate, requiring the diver to pay constant attention and “top off” with manual injection to keep up with o2 metabolism and changes with depth. The mass flow rate is verified regularly during pre-dive set up and can be adjusted by increasing or decreasing the interstage pressure (IP) of the o2 first stage regulator. The intent is to have the diver custom adjust the IP between dives initially and thus get the flow rate of oxygen to nearly match their own minimum metabolic rate… some mCCR divers get this so fine tuned that they only have to add o2 a few times during the constant depth parts of the dive.

When first looking into rebreathers, many folks, having heard that they are “dangerous”, have a hard time getting over the idea that one’s life is really in one’s own hands with a manual system. The idea of manual injection steers many people away from mCCR’s as it does not sound as safe and reliable as an automated system. Training and experience with manual injection lead many to come to the opposite conclusion. Firm believers in mCCR's often conclude that manual injection is the corner stone to safer habits and ultimately reduces overall risk. They postulate that having to monitor and adjust loop o2 balance throughout the dive entrains one to the requirements in o2 injection rate, to become more instinctive about making the necessary adjustments to changes in dive profile, particularly when something unexpected happens. In practice I have found that adjusting and monitoring on my own o2 is surprisingly reassuring and intuitive, I feel plugged in to the process. I believe that giving the brain something to monitor that actually fluctuates, as opposed to an electronic set point controller, which nearly always says the same thing, keeps one alert and motivated to check the gauges frequently and make the necessary adjustment. I have found that after a while, this process actually becomes an enjoyable challenge, a skill which one is constantly honing. It is believed that this connectedness reduces the likelihood of critical lapses in attention, inadequate reflexive reactions in times of high anxiety and ensures that a malfunction would be detected in time to adequately respond. To sum up the sentiment, many believe that the only set point controller you can trust is the one between your ears. This theory that mCCRs are safer seems to be supported by the near zero fatality rate associated with them, though reasons for this low fatality rate have yet to be empirically determined. It is interesting to find that many eCCR divers are also so convinced of the value of manual injection that they advocate running eCCR’s on a low set point and inject manually most of the time. The one thing we all seem to agree on is that the brain is the most trust worthy monitoring system and must be fully engaged nearly continuously no matter what system you choose.

MCCR’s have been known as the less expensive option and while you can get started with them on more of a restricted budget, I have found that if you compare equally capable mCCR’s and eCCR’s (equal redundancy in electronics with equal depth capacities) that they come surprisingly close in cost, all things considered. It would seem that the current trend in mCCR's development is not so much focused on maintaining simplicity or being less expensive overall, but rather allowing the user to choose the level and type of additional electronic integration, often allowing for many of the amenities of eCCR’s while continuing to require the user to inject o2 manually and continuously monitor the effect of injection, pressure change and metabolism on the loop’s po2. Some mCCR users claim that regardless of whether they are safer that they have chosen to dive a mCCR for the fact that they are less likely to malfunction due to being simpler and they have a better chance at finding a remedy for in-field repairs should something need repair or replacement. MCCR’s tend to be more modular and field serviceable, reducing the prospects of missing dives or whole dive trips. MCCR’s can be configured so that the electronics can be swapped out in field without having to be a computer technician.

Some mCCR’s are based on a design of only 2 o2 cells, diverging from the custom of having 3. The argument is that the brain can employ a much more sophisticated voting logic than a computer, by checking the cells at the beginning of a dive for current limitations and by flushing the loop with diluent to confirm which cell is responding properly when there is a discrepancy. Some manufacturers are beginning to produce their mCCR with only two cells but leave room for a 3rd. It is becoming common for the manufacturer to leave the option of additional cells and choice third party po2 monitor up to the customer. A 3rd cell is often added in this case with a completely independent po2 monitor, often combined with a decompression computer to more closely track decompression limits and as a comparison with the readings on the primary po2 display.

In response to the challenge of maintaining constant po2, most mCCR’s use a first stage on the Oxygen side that is plugged (as in non-pressure compensating) preventing it from changing much in flow rate of o2 molecules as pressure changes and depth increase. Manual injection, by the use of a simple inflator valve, is combined with a constant mass flow (CMF) valve, a nifty device that in simplistic terms meters out molecules of o2, which varies little with depth/pressure, rather than gas volume, which would fluctuate drastically in atomic density with changes in pressure. The combination of a mass flow orifice and non-depth compensating first stage helps make maintaining a more constant ratio of o2 in the mix easier for the diver. Because the spring in the first stage is blocked, however, there is a point with increasing depth where ambient water pressure will match the inter stage pressure of the first stage causing the o2 flow to cease…this is typically around 300 ft FSW. To give some buffer, a 250 ft depth rating is often given by manufacturers. Most mCCR’s are therefore considered “depth limited” in stock configuration. But the term “depth limited” is a relative term, especially if you are coming from the OC perspective, as 250 fsw is more than enough for many divers and even this can be overcome with off-board o2 from a standard, depth compensating regulator for the deep part of the dive. Both mCCR’s and eCCR’s require addressing high po2 in the same way…diluent is added, gas is expelled from the loop.

Some folks have concluded that since eCCR’s keep a more consistent po2 than someone diving a mCCR can and therefore that eCCR’s are better at fully maximizing the decompression advantages of CCR’s. Others say that the fluctuation in po2 typical of an mCCR diver’s manual injection is negligible once a diver gets good at maintaining a relatively constant po2. Critics of mCCRs say that the constant mass flow valve is a potential weak link in the chain, being prone to getting clogged. The typical rebuttal is that having a spare is cheap and they are easy to swap out and that such occurrences are rare, and since you are monitoring your po2 so much anyway that a problem would get noticed quickly, only requiring an increased rate of manual o2 injection.

Manufacturers of both mCCR’s and eCCR’s offer multiple size options (KISS: Sport and Classic, Megalodon: Standard and Mini Meg and Expedition, AP: Inspiration and Evolution). The size difference relates mostly to scrubber duration and o2 and diluent tank size. There are also front and back mounted counterlung options. Proponents of over-the-shoulder counterlungs say they offer better buoyancy, reduced work of breathing and reduced chance of Caustic Cocktail/more reaction time during a flood. Proponents of back mounted counterlungs enjoy the lack of clutter in their chest and report no difference in buoyancy… and they say the difference in WOB (work of breathing) is insignificant, except when turned on to one’s back, which is avoidable most of the time.

There are quite a few third party frames available for some CCRs, intended to help create flexibility in areas like tank sizes, weight trim and wing configurations.

A common variation in design for administering diluent to the loop is with the use of an ADV (Automatic Diluent Valve) or BOV (Bail-Out Valve). ADV’s come in two main styles, a regulator style that works just like a standard OC second stage (the purge button has been employed to allow for manual addition of diluent if needed) and a Schrader valve style that is more like a plunger that requires pressure on the plunger in order to administer gas.

Both mCCR’s and eCCR’s address the dangers of Co2 build in very similar ways. All use some kind of chemical absorbent that reacts and binds Co2, “scrubbing” it from the exhaled air. The most common type of co2 scrubber canister is Axial, where the exhaled air flows from one end to another. Radial scrubbers, one’s that flow from the inside to the outside of a cylinder are gradually becoming more popular as they can handle being flooded and still be breathable and they are also enjoyed for their increased efficiency…allowing one to use less co2 absorbent over time. There is a new kid on the block, the EAC or Extend Air Cartridge. Some rebreathers can be adapted to them and one is designed exclusively for it. See the portion on the Optima for details.

 

[almitywife]

Part IV

The Redundancy Debate

One of the areas of great debate with respect to design of all rebreathers is the need for true electronic redundancy and what design actually amounts to true redundancy. Just about everyone knows from experience with cell phones, computers and other electronics that electronics are not 100% reliable, and the more complex they are, the more likely they are to have problems. Just about every rebreather diver agrees that carying OC bail out is a must but many will debate the value and definition of electronic reduncancy. Many folks believe that a fully integrated system that lacks true redundancy can not be trusted, as a problem in one function would leave doubt about the function of the rest. True redundancy is important so that if there is a failure in one system that you still have another, presumably unaffected system to compare on and rely on for bail out, as many folks like the idea of being able to stay on the loop if they can verify that it's safe to do so. Having a completely independent po2 reading through a truly separate device in order to compare readings to determine if it’s safe to stay on the loop is considered by many to be essential. This comparing process also helps to keep the mind engaged. The other major reason for true redundancy is that you will have more options available to continue diving on a trip in a remote area after the dive has been ended and the problem identified.

There seems to be two very divergent trends in rebreather design. Some eCCRs are going in the direction of more fully integrated systems, a kind of all in one approach. Fully integrated systems offer the advantage of global monitoring of the system. The disadvantage of integration is thought to be that it leaves one vulnerable to a malfunction leading to a lock out or one element causing problems in the entire system requiring factory service before additional dives can be made. Quite a few manufacturers of both eCCRs and mCCRs are going in a very different direction with the development of more fully modular systems, with elements that can be removed and replaced if there is specific malfunction, increasing the prospects for in-field repair by the diver. For instance, some eCCRs are made in such a way that a constant mass flow valve can be easily added for running manually, quite a few divers are finding that it’s surprisingly easy to add a constant mass flow valve to the save a dive kit, leaving them with more options in case of controller failure. One manufacturer of eCCR electronics even comes stock with an mCCR's cmf valve and a solenoid…a very wise step forward in design in terms of convenience, IMHO.

At this point all eCCRs, no matter how redundant they are only have one solenoid and this leaves even redundant set point controllers vulnerable to a common failure point. MCCRs, lacking a solenoid, lend themselves particularly well to modularity because they lack such a common failure point. The disadvantage of modularity with the intent of leaving some fixes up to the diver is that they may encourage one to venture into the realm of technician, beyond one's actual abilities, in order to swap out malfunctioning aspects of the system and many people believe this is too much to expect of the average user, even arguing that this could invite divers to put themselves at unnecessary risk, and continue diving it when it should instead be sent back to the manufacturer to be worked on by a certified technician. The flip side to that argument is that modularity often means replacing something is a matter of unplugging it, unscrewing the port in the head and adding a new element and replacing it without having to do anything more technical...leaving that to a certified technician when it's convenient to send the offending widget in for proper service. Each diver has to make a call on the level of involvement and risk they are comfortable with, ultimately deciding how much it’s worth to them to have options to continue diving in the event of a malfunction.

Debates are also made as to whether a HUD can adequately act as a redundant back up. It is my opinion that for a HUD to be considered a true back up it needs to be independent (separate battery and brain) and able to communicate actual po2.

In many ways it is argued that true redundancy is a matter of both safety and convenience. More and more mCCR’s are being designed with the idea that the user will add their favored back up system for such redundancy. It is my feeling that all rebreathers should come with provisions for running them manually with a mass flow assist option if for no other reason than to give a diver options for continuing to safely dive on an extended or remote trip, should some aspect of the automatic set point controller fail where certified repair is not possible.

There are several electronics packages that are being offered by third party manufacturers for just about every eCCR and mCCR rebreather. They are often used to create added redundancy (even a 4th cell on an eCCR) or to replace the stock electronics altogether. The Shearwater GF, Pursuite and the Shearwater HUD , Hammer Head electronics , The Universal Rebreather Monitor, and the VR3 are all third party electronics that are commonly used. Third party computers are often used “in line” to a 4th cell, for additional redundancy on eCCR’s. To date it is my understanding that the Shearwater HUD is the only truly independent real time po2 HUD monitor, offering continuous po2 display with it’s own separate battery and wiring, making it a convenient and simple addition for true redundancy in many systems.

Certainly the single most impacting factor with respect to safety and CCR diving is the awareness and attitude of the diver. Ultimately rebreathers don’t kill divers. All to often what kills divers are lapses in attention and making the kind of simple mistakes that anyone at any level of training and experience can make if they become too confident and fail to maintain adequate vigilance. The best attitude to take while diving rebreathers of any kind, no matter how much experience and training one gets, is that you are 100% responsible for what is happening and you should be prepared and practiced for a variety of failure modes. Getting certified to operate a CCR takes about a week of fairly solid training and is unit/brand specific. Much of the training involves drills on how to deal with various challenges and failure modes and calculating adequate OC bail out to return safely to the surface should the unit fail during a dive.

With all the choices and opinions out there, it can be very challenging to choose a rebreather. Getting enough experience to distinguish one’s actual needs and preferences from the variety of opinions takes extensive time, and ideally, first hand experience in a swimming pool on each of the available units; or even better, to really understand the differences between CCRs you’d need to put quite a few hours on each unit in the field. This would be completely impractical for most of us because it would require getting certified for each one! Maybe when I win the lottery I’ll write that report ;~).

 

[almitywife]

Part V

The Automatic injection Rebreathers
The following list of available units is not entirely comprehensive, I invite additions and corrections.

The rebreathers that I am familiar with in the eCCR camp are the Inspiration/Evolution with Vision electronics, the Megalodon (mini, standard and expedition), the Optima, and the Prism.

The main features of distinction among brands of eCCR’s as I know them:


The Vision Inspiration and Evolution are often referred to as the creme de la creme of eCCR's...the most complex, sophisticated and integrated of them all…at the opposite end of the spectrum from the philosophy of the KISS. Both the Evolution and Inspiration come with the famed Vision electronics…an intelligent global monitoring and warning system including a HUD monitor, a warning buzzer for all detected malfuctions and a temp stick that tracks the heat given off in the scrubber and approximates scrubber duration through a graph on the screen. The vision electronics are credited as being the most user friendly, plug and play out of the box. The monitoring system helps the diver monitor proper set point controller function. The single handset displays readings from two somewhat independent controllers that, to some extent share batteries. Both units come with an integrated weights/wing/harness/counterlung configuration as one piece and don’t easily accept other harnesses/wings/counterlung configuration without significant modification. They both also come stock with a regulator style ADV, and an integrated BC inflator and octopus style extra regulator to administer bail-out gas from the diluent bottle. The main difference between the Evolution and Inspiration is size and duration...the Inspiration takes a larger scrubber and tanks. The Inspiration and Evolution come with proprietary valves and a hard case, requiring brand name tanks and valves if used in the stock case. However, there are third party frames that open up the options, not requiring one to travel with the tanks. It is recommended that they receive annual factory maintenance. They can be costly to maintain but offer state-of-the -art technology and world-class customer care. The very thing that makes the Vision electronics so appealing also makes it vulnerable to malfunction. A nifty fourth cell adapter is offered by a third party and there are rumors that one is being created that will allow the Shearwater Pursuit to be hooked up to all 3 cells for manual diving in case of a primary failure on a remote trip where factory service is inconvenient or impossible. The addition of a fourth cell adapter with the capacity to allow for 3 cell monitoring and manual injection would allow one to enjoy one of the best eCCRs with the true redundancy recommended for expedition diving.


The Megaladon has over the shoulder counterlungs , two fully independent hand sets, a po2 set point controller on the primary. This system can be used for diving in the automatic mode, or with a few modifications can also be used in an mCCR format if there is a problem with the solenoid. The electronics do not come with on board deco. It boasts tank like build quality and devoted customer care. It comes with a HUD for po2 monitoring. It also comes stock with a Schrader valve style ADV and a flow stop. The flow stop allows one to turn off the Schrader style ADV since it can administer a massive flow of diluent…not something you want to do accidentally. Built to not require a case, the Meg is becoming known for it's modularity, allowing the diver to choose everything from the type of electronics to the type of wing, to the size and type of tanks, scrubber size and the list goes on and on...not an easy set of choices for a beginner, but it has the potential to be modified as one’s tastes and diving styles change. It comes standard with an axial scrubber and a third party radial scrubber is available for the standard meg.

The Prism Topaz is a mix in philosophy between the simplicity of an mCCR and the convenience of an eCCR. It combines a simple, independent po2 display with a traditional electronic set point controller (no onboard deco). It comes with a hard back case called a cowling, clear acrylic scrubber canister (easy to tell if there is a leak) a color-coded display that can be either a HUD or a wrist mount. It has over the shoulder counterlungs. The main distinguishing characteristics of the Prism are that it comes stock with a radial scrubber and with special o2 sensors and a passive secondary po2 gauge that literally runs off the electricity produced by the sensors. All o2 sensors are basically fuel cells, which generate electricity from the reaction they have with o2, this current is measured to determine o2 concentration. The Prism employs a special high output o2 sensor that produces enough electricity to power a mechanical needle style po2 gauge…this back up display is designed to provide a comparison to the battery operated set point controller, if the primary fails, this display can be a lifeline and a trip saver, allowing for manual injection without any battery power supply. It comes with over the shoulder counterlungs and a radial scrubber. The radial scrubber distributes exhaled breath from inside a column to outside rather than from one end of a cylinder to another…as with an axial scrubber. This tends to be much more efficient, boasting exceptional duration, which can equate into fewer pails of sorb needing to be hauled to remote locations. The unit's integrated buoyancy compensator and harness assembly includes ditchable weight pockets and an alternative inflation regulator (ScubaPro Air II). The Prism technology has recently been bought out by Oceanic and a new version should be coming out soon.


Dive Rite’s Optima boasts a tried and true set point controller, the “Hammerhead” electronics. The Hammerhead has two fully independent handsets, which is generally used for diving in the automatic mode, or with a few modifications, can also be used in a mCCR format if there is a problem with the solenoid. The controller includes on board decompression. For the most part, Dive Rite has taken the approach of using already proven components, with the exception of the HUD and Scrubber. The HUD is a vibrating style called the Diva, which is designed to catch the attention of the diver if there is a problem by vibrating the mouth piece. The scrubber used employs the state-of-the-art Micropore scrubber cartridge called the Extend Air Cartridge (EAC). The EAC is manufactured from a Co2 absorbent material that has been sprayed on a Gore-Tex like mesh and rolled into a sealed cylinder, kind of like an air filter cartridge. Its fans are attracted to claims that it offers a more uniform absorption rate and reduced chance of caustic cocktail. They love the convenience when it comes time to swapping it out and are willing to pay a premium for the cartridge (about 3x the cost of standard sodasorb co2 absorbent). They can take any standard harness, particularly any one of Dive Rite’s impressive arrays of tried and true harnesses that have enjoyed the many years of R&D that Dive Rite has put into their large OC gear market. The Optima can take a variety of diluent and tank sizes.

 

[almitywife]

Part VI
The Manual Injection Rebreathers

The major contenders in the mCCR camp are the KISS, the Copis Meg, the rEVO and the Pelagian. The main features of distinction as I know them:


The KISS is designed with a philosophy of simplicity and independence in components. The name is the acronym for “Keep It Super Simple”. It comes in the Sport KISS for recreational limits and the Classic KISS for deeper diving. The KISS is responsible for popularizing the use of a constant flow orifice. It has 3 independent po2 only displays, one for each cell and each one is fully independent with it's own battery...no shared wires. It comes stock with a po2 only display, with the diver choosing either the original wrist mount or a pendant display. KISS units have back- mounted counterlungs and employ the use of a BOV, an OC regulator attached directly to the DSV (dive/surface valve). The BOV is designed to make it very easy for someone who is questioning the integrity of the loop to bail-out or take a “sanity check” on a known OC gas mix with just the turn of a valve. The KISS has a non-pressure compensating first stage on the o2 side. Many of its components are claimed to be readily available intended to make service more convenient worldwide. It employs an axial style scrubber and three o2 cells. The KISS can be matched with a variety of harnesses.


The Copis Megalodon is identical to the standard eCCR version except for the electronics and mass flow orifice. As with the standard Meg is comes with over the shoulder counterlungs , solid build, very modular, comes in mini, standard and expedition. The Copis head/electronics come stock with a KISS style constant flow orifice. It has several standard threaded ports, which makes it very amenable to mixing and matching electronics from other manufacturers. The electronics that come stock are not fully independent; all three po2 displays are housed in a single handset case and share a single battery. The po2 monitor must be calibrated each time the computer is turned on. In its stock form it is assumed that the diver is diving only to recreational depths and with adequate bail-out…additional redundancy is recommended to go beyond recreational limits. The Copis comes in a mini and standard axial scrubber and tank set up, with three o2 cells. The Copis comes stock with a strap harness, aluminum back plate and can take a variety of wings. A third party radial scrubber is available for the standard Copis meg.

The rEVO has back mounted counterlungs and a unique electronics interface that is designed to reduce potential failure points by requiring a tapping sequence to operate it rather than having traditional switches on the outside of the housing. One of its distinguishing characteristics is that it contains two scrubber sections, designed to reduce the chance of co2 breakthrough and make it surprisingly slim for it’s capacity. It has a non-depth compensating first stage on the o2 side. It comes stock with three o2 cells, and two handsets, the left rEvo dream monitors two of the cells by rotation and the right rEvo dream monitors the third cell. There is an eCCR version in development.

The Pelagian has broken from the mCCR pack and incorporates a depth compensating first stage and an adjustable needle valve. This enables the diver to adjust the o2 flow, on the fly, to allow for changes in depth/pressure making it comparable to eCCR’s in terms of depth rating in it’s stock first stage configuration. The intention is to allow the diver to make their own choice of available po2 monitors for addition to a third cell for the redundancy advised for deeper diving. It is advertised as a DCCR, or “Diver Controlled CCR”, exemplifying the added manual control it offers. It also has a unique front mounted counterlung design that boasts ideal trim. The diluent and Oxygen tanks are positioned so the valves are up at shoulder level, upside up, vs the usual design of having the tanks turned down. Many of it’s components are claimed to be readily available, intended for making service more convenient world wide. It comes stock with an axial scrubber, and two o2 cells that serve two po2 only displays. It has space for a third cell with the intention that a VR3 or other po2 monitor would be used with it for added redundancy and in line deco. It is designed so that every time diluent is added to the loop it blows across the o2 cells for faster validation and clearing of moisture, designed to improve the accuracy of the reading. It takes most any back plate and wing.

That’s it for now. I’m hoping that over time folks will make additions to this thread as things evolve.

Hope you found this helpful!

edit note:
if you would like to discuss this topic/thread, please do so here,.......
http://www.scubaboard.com/forums/rebreathers/210392-comparison-contrast-available-rebreathers.html​

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