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The oxygen rebreather (OR) is the most simple rebreather there is. The OR also is the most used rebreather in the diving market. This is because this unit is in use with many army's in the world. UPDATED 24 may 2010
The reason why the OR is the most used rebreather is because it can be dived for clandestine operations. Because the OR is a type of diving gear that does not produce bubbles it is the type used by the military all over the world. If you want to dive an oxygen rebreather you need to do a specialised course. The principle of the unit seems very basic, and in fact also is, but there are some dangerous aspects that need to be trained an known.
 

The basics:

The oxygen rebreather consists of a breathing loop usually with flapper valves that force the breathing gas in one direction. Also there is a scrubber that absorbs the carbon dioxide. The gas supply consist of a dosage system and oxygen cylinder. Finally the unit is completed with a counterlung. The counterlung is needed for the gas storage when the diver exhales the gas. Now when the diver swims he will use oxygen. Typically the oxygen consumption is :

Action

Oxygen usage

Breathing volume l/min
rest 0,3 l/min 7
slow swimming 0,7 l/min 18
medium swimming 1,2 l/min 30
heavy swimming 1,6 l/min 40
very heavy swimming 2,4 l/min 60
extreme working > 4,0 l/min >120


The oxygen inhaled by the diver is metabolized and approximately 90% of the oxygen is exhaled as carbon dioxide. This gas is forced through the valves in the direction of the scrubber. In the scrubber the carbon dioxide is chemically absorbed by the absorbent and the oxygen-poor gas follows its route to the counterlung. From the counterlung the diver inhales the next cycle and so on. When a certain amount of gas has been used by the diver he feels the need for additional gas. Depending on the system this gas is added manually or by mechanical means. It is of great importance when the diver starts diving the nitrogen content from the system is purged. This is because normal air contains 79% nitrogen. When the oxygen is used the diver still has enough volume to breath and he does not feel the need for adding oxygen. He will breath an oxygen poor mix and loses his  consciousness. Therefore is is of extreme importance the system is flushed with pure oxygen several times before he starts diving.

Warning symbol

Numbers flushing versus fraction

This is the old  version of the oxygen rebreathers explanation page. There is a new full accessible database in English now with much more info on this kind of rebreathers HERE

This page describes a CMF (constant mass flow) rebreather with manual bypass
Diagram

The Parts of the oxygen rebreather are:

  1. Mouthpiece

  2. DSV (diver surface valve)

  3. Upstream valve

  4. Downstream valve

  5. Scrubber

  6. Counter Lung

  7. Dossage unit

  8. Overpressure valve

  9. Oxygen cylinder

  10. Cylinder valve

  11. Pressure reducer

  12. Manual bypass

Through a dosage unit a constant MASS of oxygen is added to the rebreather. The quantity of oxygen is normaly just a little below the metabolic use of the diver. Usually 0,9 ltr/min. The diver breathes through the inlet valve (see # 3)  the rich oxygenmix. After breathing out the gas leaves through valve (see # 4) in the direction of a scrubber (see # 5). The scrubber removes the carbondioxide. Now new oxygen is added in the next cycle.

The dosage unit is also made in other ways:
For additional ways of adding oxygen please check this page
  
NEVER USE THE OXYGEN REBREATHER FOR DIVING DEEPER THAN 6 METERS
ALWAYS FLUSH THE REBREATHER 3 TIMES
ALWAYS DIVE IN BUDDY PAIRS
ALWAYS FOLLOW A COURSE FOR YOUR SPECIFIC TYPE OF REBREATHER

OXYGEN REBREATHERS EASILY KILL, PLEASE READ THE DISCLAIMER!
   
         
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