Different types of rebreathers

We have seen in a previous article (see "Rebreather: advantages and disadvantages") what a rebreather is of scuba diving with the basic principles, its interest and also its limits. We will try to introduce you in a slightly more advanced way the different types of recyclers.

What exists ?

As you have just seen, there is not only one type of recycler and one could say that there are as many recyclers as there are users or at least manufacturers because each machine is unique with its specificities. Three main types of recyclers are distinguished: pure oxygen, semi-closed rebreathers (SCR) and closed circuit recyclers (CCR).

Oxygen Rebreathers

These are the simplest of the CCRs, only one diving bottle is connected. This bottle contains oxygen (O2 more precisely) pure that the diver will breathe in the machine, the lime will filter the carbon dioxide and the oxygen metabolized by the organism will be replaced by that coming from the bottle. The advantage with these recyclers is that you always know what you breathe. The limits with this recycler come from the physiological properties of O2. It is therefore strongly advised not to exceed 6m of depth with this type of device. These recyclers, often worn in front of them, are mainly used by the combat swimmers of the armies (example: Aqualung FROGS).

What is a semi closed rebreather exactly?

Semi-closed recyclers allow the use of other gas mixtures. There is always a single bottle connected at the same time. To compensate for the diver's O2 consumption, an automatic injection by continuous leakage (eg the Dolphin Draeger) or by injection proportional to the respiratory rhythm renews the volume contained in the rebreather on a regular basis (eg GEM Kiss). The rebreather is then purged automatically when the false lungs are full. The advantage of these machines is the increase in autonomy multiplied by between 3 and 10 on average compared to using the same bottle in open circuit. To realize, it's like using a bottle of 2l instead of a 15l with a conventional regulator for the same dive. With little or no electronics, semi-closed rebreathers are very reliable. These rebreathers are less encountered nowadays except for demining divers and some speleologists. With the technological advances of recent years, closed recyclers have increased reliably to the point of dethroning those semi-enclosed.

APDiving Evolution Rebreather

The supremacy of multigaz closed rebreathers!

Indeed with a fully closed circuit rebreather you have to check that the breathing mixture you are composing all along your dive because it is paramount to make sure of its composition. On these models two diving bottles are connected, one of pure dioxygen and one of diluent to allow to exceed the limit 7m depth when one has that the bottle of O2. This makes it possible to have the most optimal mixture with a ppO2 (partial pressure of oxygen) constant whatever the depth of evolution which improves the decompression. The injection of oxygen and diluent must therefore be finely managed. Closed recyclers exist in two forms, mechanical (mCCR) or electronic (eCCR) but sometimes both (hybrids). The mechanical ones are piloted entirely by the diver and require great vigilance, the electronic ones inject the quantity of oxygen necessary to maintain a minimum ppO2. But do not fall asleep either with an eCCR and make sure of all its parameters and not to breathe too much oxygen either. These rebreathers are the most frequently encountered at the water's edge and the most sold by manufacturers. Their efficiency is even higher than semi-closed rebreathers. These machines allow very complicated immersions or impossible to implement in open circuit.