Diving equipment

What is a scuba diver and what does it do?

"SCUBA", meaning scuba diving, is an abbreviation of the words - self-contained underwater breathing apparatus. The initials "SCUBA" originated in 1939, in the United States, to send breathing apparatus to military divers. Just like with radar, these abbreviations became so familiar that they were often no longer written in capital letters, but began to be used as a stand-alone word, for example, in Welsh it is used as "sgwba". The scuba diver provides the scuba diver with the breathable gas needed underwater.

Nowadays, two types of scuba divers are distinguished

Open loop

Open-loop apparatus in Europe, but not in the United States, is often referred to as "scuba diving," Aqua-Lung. In it, the diver inhales from the device and exhales the air back into the water. This type of equipment is relatively simple, which makes it cheap and safe. Open cycle diving is shorter than rebreathing, depending on the weight and volume of the machine. It is uneconomical to use expensive gas compounds such as helium or trimix. Many divers use standard air (21% oxygen, 79% nitrogen). The cylinder is almost always pulled backwards. The "twin apparatus" with two cylinder backpacks was more common in the 1960s, twin cylinders are usually used by skilled divers due to the increased diving time with which they provide the diver. These underwater items were sold by air sports divers, which consisted of three-cylinder backpacks. Sometimes beer divers tend to hang these cylinders in front of them.

Closed loop

Also called rebreathers. In this case, the diver inhales from the apparatus and exhales back into it, where the exhaled gas is processed to make it breathable again. Since 80% or more oxygen remains in the normally exhaled gas, it can be concluded that the gas is used very sparingly in rebreathers, making the diving process longer and the cost of special mixtures cheaper, which is required for more complex technologies and wider training and experience needs. , twin closed - loop and fully closed - loop rebreathers.

Both types of scuba diving involve the supply of air or other breathable gas, usually from a high-pressure cylinder strapped to the diver's body. Most open cycle scuba divers and also some rebreathers have appropriate regulators that control the supply of breathing gas. Some reboilers, like jets, only have a constant supply of air. Sometimes divers use the word "scuba" to refer only to open-loop equipment.

Open loop apparatus

Newspapers and television often misrepresent open-loop scuba diving, calling it the "oxygen" supplier, probably because of its indirect resemblance to aircraft pilot oxygen cylinders. Until very recently, in the 1990s, the use of enriched air nitrox was widely accepted, and almost all sports divers still used simple compressed air. Technically, it allowed the scuba industry in the United States to remain intact from the Food and Drug Administration (FDA), which bans the use of air gas mixtures to treat or prevent disease. The use of exotic gas mixtures is currently intended to suppress decompression sickness in diving, but officially, the FDA believes that scuba divers use only compressed air.
At partial pressure, about 1.6 atmospheres, oxygen becomes poisonous. Open-cycle scuba diving can supply a variety of breathing gases, but rarely pure oxygen, except during decompression, in technical diving.

Some divers use enriched air nitrox with a high percentage of oxygen, usually 32% or 36% (EAN32 and EAN36, respectively). This allows them to stay under water for longer because its body tissues absorb less nitrogen.

With the required regulator

This type of apparatus consists of one or more diving cylinders containing a breathable gas which connects to a diving regulator at high pressure (usually 200-300Bar). The regulator supplies the diver with the required amount of gas at the appropriate water depth. Colloquially, this type of respirator (depending on the English-speaking country) is often referred to as the aquapulmonary, although the word 'Aqua-Lung' is the exact name of a product protected by the Cousteau-Gagnan patent.

"Twin tube" open cycle scuba

This is the first type of valve required for diving, which came into general use, it could be seen in typical 60's scuba adventure shows, such as "Sea Hunters".

For this type of apparatus, two (or usually one or three) stages of regulators are contained in a large valve arc mounted on the top of the cylinder backpack. This type is characterized by two wide breathing tubes, as in many modern rebreathers - one for inhalation, the other for exhalation. The exhaust pipe is not intended for inhalation, but because the air extraction must be at the rear, at the same depth as the second stage bulkhead of the regulators, in order to avoid pressure changes. This causes a free flow of gas, or additional breathing resistance, in line with the diver's position in the water, and modern single-pipe apparatus has avoided the intended second-stage movement of the regulator in front of the diver's mouthpiece. The twin tube device comes with a mouthpiece, a full face mask is an option. Another option is a mouthpiece that is connected to the scuba tube and a valve to connect the scuba and tube.

The comics show thousands of images that incorrectly depict two-cylinder twin-tube scuba dams, with one wide breathing tube coming from the top of each cylinder, without a regulator.

"Single tube" open loop scuba

Most modern open-cycle scuba machines have diving regulators that consist of a first-order pressure relief valve located above the scuba cylinder power valve. This valve distributes the pressure in the cylinder (which can be higher than 300 bar) at a constant lower pressure, about 10 bar above the ambient pressure, which is used in the "low pressure" part of the system. A relatively thin low-pressure pipe connects it to a second-stage regulator or the required valve in the mouthpiece. Exhalation takes place through a one-way septum in the required valve chamber, directly in the water, quite close to the diver's mouth. This type is called "single pipe". The first model of this type of scuba was the Purpoise (Dolphin), made from a scuba machine made in Australia.

All modern scuba machines have a spare second stage valve located on the second tube, this configuration is called an "octopus" because it usually comes out of the top of the master cylinder with many tubes for different tasks. The second "second-stage" regulator, or "backup air source", or "additional safety" or "second safety", is usually yellow (signaling its use as a backup or emergency device). It is usually pulled in a special friction plug on the diver's chest. Here it is easy to grab it, or offer it to another diver, when he needs air. In this way, this second mouthpiece allows two divers who have to share one cylinder to breathe each of their mouthpieces. The original "octopus" idea was conceived by Sheck Exley as a single swimming kit for beer divers to distribute air in a narrow space, but is now used as a standard kit for recreational diving. Modern "octopus" main level regulators are characterized by high pressure ports used with computer sensors, and additional ports for additional low pressure pipes to inflate the buoyancy kit mechanisms.

Increasingly, in the 21st century, additional "safety" mouthpieces were combined with an inflator and pumping component, a buoyancy compensation mechanism. Some diving schools recommend that a diver first give his or her mouthpiece to the person in distress while using an extra safety mouthpiece. This is because a diver who is not in an accident has much more time to group his equipment after a loss of breath.

Cryogenic open cycle scuba diving

There have been several cryogenic open-loop scuba designs with liquid air tanks instead of cylinders.
Jordan Klein modeled the cryogenic open-loop scuba "Mako" and created an almost prototype for it.
Russian Cryolang (From Greek cryo- (frost) + English "lung") was copied from Jordan Klein's "Mako" scuba. Janwillem beach rebreathers feature pictures of 1974 Kriolang. The duration of diving is probably a few hours. It must be filled immediately before use.
The SCAMP (Supercritical Air Mobility Pack) is a surface-to-air liquid air open-circuit breathing apparatus modeled by NASA to fit into a space suit.


In rebrizers, the gas exhaled by the diver is stored "counterlung" between breaths. In some rebrizers, a non-return valve directs the gas directly through the "loop". In other rebrizers, the inhaled and exhaled gas goes back and forth through a single tube, called a valve system. The oxygen used by the diver is usually replenished from the cylinder, the carbon dioxide exhaled by the diver is removed by passing gas through a purifier: a tin can filled with soda lime. The gas is then valid for re-inhalation. This type of scuba diving is known as the "closed loop".

The economical use of gas by rebreathers, usually 1.6 liters of oxygen per minute, allows them to stay underwater for longer than is possible with open-cycle equipment, where gas consumption is at least 10 times higher. Despite the fact that with oxygen rebreathers the maximum diving depth is about 6 meters / 18 feet, with some fully closed type rebreathers, diving depths of up to 100+ meters / 330 + feet are possible when using a helium solvent. The main limiting factors for rebreathers are the duration of the carbon dioxide purifier, which usually operated for about 3 hours, and the efficiency of the purifier at depth.

Duration of diving

The duration of the open cycle dive depends on the capacity (gas volume) in the cylinder, the diving depth and the diver's breathing regime.

An open-cycle diver with a respiration rate above ground (atmospheric pressure) of 15 liters per minute will use 3 * 15 = 45 liters of gas per minute at a depth of 20 m. [20m / 10m per bar) +1 bar atmospheric pressure] * 15 L / min = 45L / min). If an 11 liter cylinder filled to 200 bar is used up to a reserve of 17%, then there is (83% * 200 * 11) = 1826 liters. At 45 L / min, the duration of the deep dive will be a maximum of 40.5 minutes (1826/45). These depths and times are typical for experienced sports divers who want to explore coral reefs in a leisurely way, using 200 bar aluminum cylinders rented from commercial sports divers' associations in tropical islands or seaside resorts.

Diving with a closed-loop reedger is about three times longer than with an open one; the gas is recycled, but fresh gas is independently supplied to replace the oxygen used, and any excess gas is released. Because this type of machine uses gas more economically, the diver has to hold smaller cylinders in terms of weight. Still, the closed-loop system allows diving that is twice as long as open-loop diving (approximately 2 hours).

Divers who use oxygen rebreathers consume about 1 liter of oxygen per minute, which is as much as fully enclosed rebreathers. Except during ascent, when a fully closed loop rebreather that functions properly does not actually use solvent. So a diver who has a 3 liter oxygen cylinder filled with 200 bar and who has left 25% in reserve has the opportunity to dive for 450 minutes (3 L * 200bar * 0.75 / 1). The limiting factor for this diving is that the shelf life of the purifier soda lime is shorter.
In practice, the duration of diving is influenced by various factors, such as water temperature and safe ascent requirements.

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