Karl´s Rebreather Page

Principles

Preliminaries

Oxygen-Rebreather

Chemical-Mixedgas-Rebreather

Semiclosed-Rebreather

Active Flow

Passive Flow

Electronic-Closed-Rebreather

Liquid-Rebreather

Skaphander

The Prelimary of any modern Rebreather is just a Bag that is operated as Counterlung. This system was already in use more than 2000 years ago. The trick is quite simple: breathing is stimulated by stress and CO2, fainting by lack of Oxygen. So it´s easier to breath into and from a bag than to stop breathing the same time although it does not really prolong the Oxygen. Breathing from the Live-Jacket, rebreathing and changing the gas any 4th breath was (by principle) the next step. This could prolong 100barl to last up to 10minutes (depends on depth, training etc.).
Classical Helmet-Diving works just the same way: the pump on the surface brings down enough bar*l air to give the diver enough Oxygen to preserve fainting, the divesuit is also in function as counterlung, and sometimes a wet flannel towel with tartar (Potassiumhydrogentartrat = Kaliumhydrogentartrat) already acts as CO2 Absorber ("scrubber").

Oxygen-Rebreather are the next Step. They just realize the fact that the body needs O2 and dumps CO2. It depends to the intended purpose if the O2 is added manual, if required or by constant flow. The IDA57 is a tiny oxygen-rebreather. In most Oxygen Rebreathers for SCUBA usage the O2 is added if required by an under-pressure triggered demand valve. Manual Add was used on submarine escape units, constant flow on fire escape units and by oldtimers (because they called gases "Oxygen" what we would call "Nitrox" or "Hydrox"). The CO2 is absorbed, in most cases by lime. It is vital essential to keep the loop clean of other Gases than O2 to prevent fainting. This means getting rid of Nitrogen that was in the Lungs before the dive, the Nitrogen that was in the body of the diver and "dirt" that was in the Oxygen tank. High Oxygen partial pressures are toxic, this causes the limits in using time and depth.

Chemical-Mixedgas-Rebreather extend the range, because they allow to use mixed gases in a simple circuit. A chemical produces O2 while consuming C02. The most popular of those Rebreathers is the Navy CCCR from CCCP the IDA71. How deep you can use those Rebreathers depends on the diluent you use, but also don´t forget to keep the loop clean.

Semiclosed-Rebreather (SCR) are in use since about 1726, long before Cousteau and Gagnan developed the Aqualung. The CO2 is scrubbed out by lime like in the O2-Rebreather, the difference is how Gas is added:
Active Flow (CMF-Rebreathers): The Dräger-Atlantis (new name: Dräger-Dolphin) is such an SCR. A constant mass-flow of mixed gas is added to be sure that the diver gets enough oxygen (O2). That´s why those Rebreather produce bubbles: a sure amount of Nitrox (or for deep dives: Trimix) is added and the over-volume is dumped.
Passive Flow means that the amount of added mixed gas depends on how much the diver breathes. Passive flow semicloed rebreather in most cases bubble less than the active-flow type. A Passive Variable Ratio-Biased Addition Semi-Closed (PVR-BASC) like the Halcyon-Rebreather is keyed to your Respiratory Minute Volume (RMV) and to the depth you dive in, it does not change the same ratio of gas per breath, it changes the same mass of gas (bar*l) per volume (liter) you breath.

Electronic-Closed-Rebreather are controlled by an electronic unit, they make no bubbles. (Sure, when you ascend and dump expanding gas this makes some bubbles.) The electronic sensor measures the oxygen partial pressure (ppO2) and the electronic adds O2 to the breathing loop by triggering an electromagnetic valve (the so called "solenoid") when nessesary, the CO2 is scrubbed out by lime like in the O2-Rebreather. ECCR´s have two bottles with gas: 1) the oxygen, to be added by the electronic and 2) the diluent gas, to be added manually or by volume control. The "Buddy Inspriation" is a CCR (fully Closed mixed gas Circuit Rebreather) with manual diluent add, it allows to dive the twilight-zone when using trimix as diluent gas.

Liquid-Rebreather do not use gas to ventilate the divers lungs but special liquids, this allows unlimited deep diving, even without decompression stops. It is unknown if that is still science fiction like in the movie "the abyss" or if it is/was in military use. Liquid ventilation already is in hospital use, the chemical named "Liquivent" is manufactured by Höchst. I heared about diving experiments in 1994 that were abandonated due to problems with CO2 and with eye sight (how to see without an gas-bubble for the eyes / how to decompress the eyes in the case of having used a gas bubble). It is known that Liquid-Rebreathing can not solve the HPNS-Problem.

Rebreather-Index