A rebreather (closed circuit diving system) is a piece of equipment designed to rebreathe the air or other gas you breathe in during a dive without exhaling it. While doing this, it absorbs the carbon dioxide in your exhaled breath with a chemical (soda lime) and adds oxygen as much as the oxygen that has decreased. In this way, we can stay underwater for hours with a high rate of gas savings.
If we recall from our open water or advanced scuba diving lessons, while the oxygen in the air we inhale is 21% and nitrogen is 78%, the air we exhale still contains at least 16% oxygen. Nitrogen is still the same, 78%. Of course, the decreased oxygen is replaced by 5% carbon dioxide. The device we call a rebreather basically absorbs this 5% carbon dioxide and adds oxygen instead. Well, in this way, the 95% of the air we breathe, other than the 5% we use, does not go to waste by becoming bubbles in the water. Especially if we are diving with trimix that includes helium, it is a total shame, the bottle of helium costs I don't know how many dollars (I try to forget every time).
If what a rebreather is is starting to become clear in your mind, let's get to the facts and details. A rebreather system, although it may have dozens of differences depending on different brands and models, basically has the following main components:
Breathing hose and mouthpiece
Diver surface valve - dsv
Counterlung
Scrubber canister
Oxygen Cylinder
Diluent Cylinder
Breathing hose and mouthpiece; It is the component that provides one-way gas flow and allows the diver to breathe the gas in the circuit with a mouthpiece in the middle.
Diver Surface Valve - DSV; It is the component that allows the circuit to be closed from the mouthpiece on the surface, allowing breathing from outside and preventing gas in the circuit from escaping. At the same time, when it is necessary to remove the mouthpiece underwater, the diver's surface valve is closed to prevent water from entering, thus keeping the circuit closed.
Counterlung; It is one of the most critical components of the rebreather system. The design should be such that the entire gas volume that the diver breathes in a single breath can be provided by these breathing bags (counterlung). Many rebreather systems have two counterlungs; an inhaling bag and an exhaling bag. As the diver exhales, the lung volume will decrease and the volume of the exhaling bag will increase. As the diver breathes in, the volume of the breathing bag will decrease and the lung volume will increase. In this way, with the lowest possible breathing effort, the total gas volume will remain constant between the diver and the unit, and unlike open circuit scuba, there will be no effect on buoyancy during breathing.
Scrubber canister; It is the component that contains the carbon dioxide absorbing chemical. In the circuit, the gas in the exhalation counterlung passes through the canister, the carbon dioxide is absorbed and oxygen is added to the loop.
Oxygen Cylinder; The cylinder which the pure oxygen added to the system is kept. While it is generally 2 - 3 liters in volume, cylinders with different volumes up to 12 liters can also be integrated in various brands such as JJ CCR.
Diluent Cylinder; It is the cylinder that carries the gas that we will dilute pure oxygen with during diving. Likewise, they are generally 2-3 liter volume cylinders.
Essentially, all rebreather systems are designed to save more gas, and they do this very efficiently. They differ from open circuit scuba diving in two main ways.;
Since there is almost no gas release in the system except for the ascends the surface, it provides much more gas savings and allows staying underwater for long periods.
In open circuit systems, gas mixtures with a fixed oxygen ratio can be used, while in closed circuit systems, gas mixtures with a fixed oxygen partial pressure and therefore variable and with the highest breathable oxygen ratio can be breathed.
In other words, with a closed circuit system, we breathe different gas mixtures at each depth. Thus, we breathe the highest amount of oxygen we can without getting oxygen poisoning, which dramatically reduces deco times. We will examine this topic in more detail in future articles.
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