Gill Envy
Contributor
EDIT NOTE, 17th Dec 07!
With permission from author, an updated version of this article can be found here,
http://www.scubaboard.com/forums/re...ntrast-available-rebreathers.html#post3268083
With permission from author, an updated version of this article can be found here,
http://www.scubaboard.com/forums/re...ntrast-available-rebreathers.html#post3268083
How to compare and contrast the available rebreathers on the market is an eternal question and the answers are constantly evolving with changes in market trends. Few people really want to answer this question because few people own all the rigs. I do not own all the rigs and I am by no means an authority on the subject but I have owned two very different types and gotten considerable hours under my belt. I have put some time and energy into explaining the major differences as I have observed them. This list is not comprehensive, is not all first hand knowledge… but I thought it might be helpful to folks just starting on the path of gathering knowledge.
There are two main differences between available CCR's. there are those that require manual o2 addition (mCCR's) and those that rely on an electronic set point controller with a solenoid to monitor and inject o2 in the loop (eCCR's). Manual vs electronic only refers to the o2 injection as manual injection rebreathers are becoming more and more electronic with in-line deco, HUD's (heads up displays) and more integrated electronics, but continue to adhere, with near religious conviction, to leaving out the solenoid/ automatic set point controller. To ease the injection process a constant flow orifice or “leaky valve” is used to administer some o2 into the loop, requiring the diver to “top off” with manual injection to keep up with metabolism. It would seem that the trend in mCCR's is not so much in maintaining overall simplicity anymore but rather continuing to require the user to inject o2 manually and continuously monitor the effect of injection and metabolism on the loop’s po2.
Many of the firm believers in mCCR's have concluded that manual injection builds safer habits, as monitoring and adjusting loop o2 balance becomes deeply engrained in the diver, reducing the likelihood that a malfunction would go unnoticed. For reasons yet to be determined there is a near zero fatality rate associated with them which seems to support this conclusion. Many users simply like the fact that they have a better chance at finding a remedy for in field repairs since they are simpler, reducing the prospects of missing dives or whole dive trips.
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 over task loaded or distracted. Eccr's seem particularly attractive to photographers and deep penetration wreck divers and cave divers, those for whom hands free function is a high priority. For reasons yet to be determined, there are many fatalities associated with eCCR's, which could reflect their added complexity, additional failure points, their tendency to tempt an "auto pilot mentality" or other factors yet to be determined (more people dive eCCR's, dive them more aggressively, possible need for changes in training standards, etc. etc.). the best attitude to take while diving any rebreather is that you are 100% responsible for what is happening.
The major contenders in the mCCR camp are the KISS, the Copis Meg, the rEVO and the Pelagian. the main features of destinction as I know them:
-The KISS (the name taken from the military acronym Keep It Simple Stupid) is built with a philosophy of simplicity and independence in components. 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 has back mounted, internal counter lungs (not ideal for bueyency or WOB, but reduces clutter to the chest). the KISS has non-pressure compensating first stages, which means it is depth limited in it's stock form, though this can be overcome with outboard o2 for the deep part of the dive. This can be the case for all non-depth compensating rigs. The reason for the non-depth compensating first stages is to help keep po2 relatively constant as pressure increases with depth.
-the Copis Megalodon is identical to the standard eCCR version except for the electronics...front mounted counter lungs, solid build, very modular. 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, the displays share a case and the battery. In it’s stock form it is assumed that the diver is diving only to recreational depths with adequate bail out…additional redundancy is recommended to go beyond recreational limits. it has a non-depth compensating first stage, which means in it's stock form it is depth limited, again that depth limit can easily be overcome with off board o2 with a depth compensating reg to be plumbed in for the deep part of the dives.
-the rEVO has back mounted counter lungs, a unique electonics interface that is designed to reduce failure points. One of it's destinguishing characteristics is that it contains two scrubber sections, designed to reduce the chance of breakthrough. It has non-depth compensating first stages. There is also an eCCR version...the rEvo dream.
-the Pelagian has broken from the mCCR pack and offers a depth compensating first stage and an adjustible needle valve...allowing the diver to adjust, on the fly, the 02 flow to allow for changes in depth/pressure making it presumably appropriate for diving to practically any depth. it also has a unique front mounted counter lung design that boasts ideal trim. Many of it’s components are claimed to be readily available making service more convenient world wide.
-there are several electronics packages that are being offered by third party manufacturers that are often used to create added redundancy or replace the stock electronics altogether. The Shearwater, Hammer Head electronics, Universal Rebreather Monitor and VR3 are all third part electronics that are commonly used with eCCR's and mCCR's. Third party computers are often used with a 4th cell, for additional redundancy.
The rebreathers that I am familiar with in the eCCR camp are the Inspiration/Evolution with vision electronics, the Megalodon, The optima, and The Prism. One of the main distinctions among eCCR’s is weather they include truly independent handsets and weather they come stock with in line deco computers. The main features of distinction among brands as I know them:
-The Vision electronics are often referred to as the crem de la crem of eCCR's...the most complex and sophisticated of them all. They apparently dominate the current market. The main difference between the Evolution and Inspiration is size and duration. The inspiration and Evolution come with proprietary valves and a hard case, requiring brand name tanks and valves if used in the stock case, though there are third party frames that open up the options so that you don’t have to travel with the tanks. It comes with a temp stick to help confirm scrubber duration, a HUD (heads up display) and buzzer to help confirm proper set point controller function, onboard deco and a somewhat independent set of controllers. They require annual factory maintenance, and being more complex, it's usually back to the manufacturer for fixes as well. They can be costly to maintain but offer state of the art performance and impressive customer care. They have an apparent low mortality rate associated with them, at least the Vision version though it’s hard to determine mortality rate with any rebreather brand because manufacturers unfortunately hold on tightly to total sold unit numbers and mortality figures. The original classic version is often referred to as the YBOD, or yellow Box of Death as many people perished while using them. One of the big suspected culprits of the classic was the excessive tolerances in the scrubber…allowing for co2 bypass.
-the Megaladon has front mounted counter lungs, a po2 set point controller, no on board deco. It boasts tank like build quality and devoted customer care, even assistance with in field repair. It comes with a HUD for po2 monitoring. Built to not require a cover, the meg is becoming legendary 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 and 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 well into the future, as new advances are made and ones tastes and diving styles change.
-the prism is a mix in philosopy between the simplicity of an mCCR and the conveneience of an eCCR. It combines a simple, independent po2 display with a traditional electronic set point controller. The distinguishing characteristic of the prism is that it comes with special o2 sensors. All o2 sensors are basically fuel cells, which generate electricity from the reaction they have with o2, this current is measured and a concentration extrapolated. The prism employs a special high output o2 sensor that produces enough electricity to power a mechanical needle style po2 guage…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. It comes with front mounted counter lungs 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.
-diverite’s Optima, boasts a tried and true set point controller, the hammer head electronics with two independent displays. For the most part, diverite has taken the approach of using already proven components, with the exception of the scrubber, which employs the state of the art micropore scrubber cartridge called the Extend Air Cartridge (EAC). An Co2 absorbent material that has been sprayed on a gortex like mesh and rolled into a cylindar. It’s users love it’s convenience and are willing to pay a premium for it. The optima is more modular than the inspo/evo in that it can take any standard harness, particularly, any one of diverites impressive array of tried and true harnesses that have enjoyed the many years of R&D that Diverite has put into their large OC gear market.
Hope that is helpful. Please add corrections or additions!
EDIT NOTE, 17th Dec 07!
With permission from author, an updated version of this article can be found here,
http://www.scubaboard.com/forums/re...ntrast-available-rebreathers.html#post3268083
With permission from author, an updated version of this article can be found here,
http://www.scubaboard.com/forums/re...ntrast-available-rebreathers.html#post3268083
