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This post disappeared from the "dressing for tech" thread so I thought I would start a new thread for the RB80. This is a very DIR specific rebreather so I believe this section is where it belongs.

Quote from FreediveWI
"Not being an expert on all forms of rebreathers I'll still take a stabe at the RB80 question. It's my understanding that the gas usage,and dosage, on the RB80 is directly tied to the divers own work of breathing. This cannot be said for other SCR's, like the Dolphin or the Ray, which can have widely fluctuating F02's in the bag due to work load. The RB80 is tied to the workload so the F02 stays much more constant. From what I understand this is the reason for one rebreather over the other.

Maybe you can help me out with this. I "thought" that the Gator, or the Frog, was suppossed to work on hte same prinicple, but can't remember for sure."


You are pretty much on the money with the RB80. It is the only true RMV keyed rebreather on the market. What is unique about it is a bellows designed counterlung which sits on the bottom of the canister. When the diver exhales the bellows fills and a portion of the exhaled gas is trapped (with moisture) in a series of check valves and then jettisoned with the following inhalation.

The greatest advantage of this system, as you mentioned, is a much more stable FO2. This can be within 8% variation on the surface and as low as 2% over 80fsw. The disadvantages are the amount of offboard gas needed for optimum PO2, and a "relative" loss of efficiency compared with other RB's because gas use is directly related to the divers breathing rate. At least one of the deaths on an RB80 was due to an OOG situation.

To a diver used to wearing doubles the RB80 will seem very intuitive. As was mentioned it is noticeably larger and more cumbersome than many other RB's, but nevertheless still a viable player in the RB market. If it was priced more reasonably it would likely be more popular but $8,000 is a bit high for an SCR. It has a built in OC DSV (open circuit dive surface valve) which means to go "off the loop" from SCR and OC is merely the flip of a switch. Definitely a nice feature, but it does add bulk to the mouthpiece.

As for the FROG it is a complete POS! I have seen the unit at a number of trade shows and how people are not killing themselves on the unit is a mystery to me. The design flaws in the unit are too many to list here, but the scrubber is the biggest concern. The canister is roughly the size of a large soup can, contains about 1/5 the amount of scrubber material than the Inspiration yet they claim a 3 hour duration? :o The canisters themselves are "disposable" and look like they were made in arts and craft time at the local kindergarten. To answer your question the FROG runs more along the lines of a KISS style rebreather and is not RMV keyed.

Hey thanks Chuck,
You beat me to it. When we were in Costa Rica diving in September, we had a diver on an RB80. One of the things I didn't like about it was that he spent more time on maintenance than the rest of us on CCR's. One of the biggest advantages SCR's usually have over CCR's is their simplicity, but the RB80 has so many moving parts that you lose that advantage.
Please feel free to correct me if I'm wrong, but doesn't the RB80 have manually controlled check valves on the dil/o2 supply lines that the diver themself can manually turn on and off? What I didn't like about the unit was that if the diver was in a tight squeeze where the environment contacted and turned, or the diver reached for the wrong knob and accidently turned the wrong valve, a serious problem to have to deal with might occur? These lines are simply coated red and green, and to me could be very hard to distinguish in low light, low vis. Other than not relying on computer controlled inspiration or voting logic, I don't see how these possible diver or environmental error-prone valves could be considered DIR?

Please feel free to better educate me.


The RB80 doesn't have DIL/O2 - just two supply bottles of bottom mix and off-board gasses that can be plugged in, so no worries about rolling off one tank and just getting O2 in the loop. Basically it's a set of doubles with a gas extender in the middle. Roll offs when contacting an overhead environment are exactly the same as with a regular set of doubles. The RB80 was designed with a very specific goal in mind: cave exploration. DIR is all about bringing the right tools for the right job and that's what the RB80 is all about. As far as its size is concerned, it is bigger than some of the CCR's on the market, but if you're riding a magnum Gavin, towing 2 or 3 more and hauling 5-6 stage bottles (if not more) the size of the RB becomes very relative. There's a very detailed description of the unit on .
Here's a link to a RB80 rebreather site:

The website also includes "DIR Tips".

As DRE already clarified, the "oxygen problem" does not exist. The RB80 is SCR not CCR. The highest PO2 gas you could possibly breathe is based on the analyzed FO2 in the bottles you have plugged in. Wink The back gas consists of two cylinders of whatever size you prefer. They are connected by a manifold so the gas would be identical in both cylinders. I have heard of divers side mounting the system and therefore removing the manifold, but I am not sure if that reflects the true design of the unit. The efficiency of the RB80 would make AL40's the equivalent of almost 400ft3 of gas. The only time you would plug in an oxygen whip is when you where doing deco, and of course you would be at the appropriate depth to avoid O2 issues.

Features like a 10 hour canister (the longest duration for a "stock" unit) and the moisture removal process reflect the RB80's design fundamentals (cave exploring). DRE's example of the scooter and bottle laden RB80 diver is fairly accurate. With the RB80 you would need to carry a separate bottle for every gas you wanted to breathe. The real advantage here is getting more time out of your cylinders. The true role of the RB80 is as a gas extender. The same benefits can be produced on a CCR with fewer encumbrances, and if a Halcyon CCR is released I am sure it would be an interesting unit. If a CCR with the same intuitive operation and rugged construction of an RB80 were available I think GUE would endorse it.
I feel people can be too quick to dismiss the RB80, partially because they dislike the people associated with it. The truth is there are as many "benefits" as "drawbacks" to the RB80 and there is probably enough demand for it to increase its presence in the rebreather market.


I have looked briefly at the design of the RB80, as I recall it was referred to as something like a "keyed RMV" system.

Is the size of the exhaust bellows in the counter-lung adjustable so that you can "tune" it to a particular diver, or is it fixed?


With the RB80 you can set the amount of gas is added to the loop with each breath, i.e. the inner bellows discharge can be set in relation to the total volume of the outer bellows. Factory setting is 10:1, which is brought down to 8:1 in realtime operation due to some loss clearing the mask, exhaling through the nose upon ascent, etc. Apparently, it is possible to set it so the ratio increases, but it becomes much harder then to notice some of the passive failure modes right away.


Which version of the RB80 are you familiar with?



Which version of the RB80 are you familiar with?


From GI on Dirquest:

"The original [i.e. the old PVR-BASC rebreather] was supposed to shrink the inner bellows with depth and therefore give you an increasing ratio as you went down so that your actual
gas consumption at any depth would be the same as at the surface. Even with Bill Gavin's changes to the system ( which were of course very clever ), it was still too big. I artificially reduced the throw on mine and made it much smaller, but that did me no good since my partners were still four inches higher. Reinhard [Reinhard Buchaly - the RB in RB80] came up with the current design, which is much smaller and does not
have the variable ratio. What he does is change the bellows assemblies for different dives ( smaller discharge bellows for greater ratios, larger for lower ratios)

So it is fixed but changeable depending on what useage you would like to get from it. Thanks for pointing it out Chuck - I knew you could change the ratio but didn't remember the exact details.

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