In ancient times, people could only rely on their stamina and courage when trying to dive underwater (e. G, for hunting purposes). The first mention of technical devices for diving is found in Aristotle's works. He writes that during the time of Alexander the Great, divers could breathe underwater, they used some kind of a pot in which air remained. In essence, this inverted pot was a prototype invented in the XVI century.
As the name implies, it is the same air breathed on the surface (21% O2, 79% N2), which is filtered to remove moisture before compression in the cylinder. For some types of diving, cylinders can be filled with other types of gas mixture (e. G. Nitrox, trimix, etc.), specific technical diving knowledge is required.
Necessarily, when the cylinder is filled with another kind of gas mixture other than compressed air visual identification alerting the diver of its contents must be shown. The cylinder is typically constructed from steel, but there are some made of aluminum to keep the weight light.
Vented equipment provides the diver oxygen due to the continuous supply of compressed air from the surface through a flexible hose. The air is periodically discharged into water (vented). Three-bolt diving equipment finds its use mainly in marine environments at intermediate depths. Most often used for various rescue and salvage operations.
Since no arms are used in underwater swimming leg movement is responsible for the displacement of water. Made of rubber or silicone, the fins may be of two designs: open heel, which almost always requires the use of a boot inside the fin and a closed heel. They vary in size according to use, as a rule there is the large (jumbo) for snorkeling, since higher speed is required for the diver to reach the desired depth. And there is no air supply beyond the limits of lungs.
The dive knife is considered a safety tool. If a diver gets tangled up in the background on some string or fishing line, the knife will be essential to free him from trouble. The diving knife can also be used as a hammer, screwdriver, saw and even yardstick. Its use is especially autonomous, and should not affect marine life. However, in practice hunting, the knife is useful for cutting and removing fish caught.
Helium-oxygen equipment is also equipped with a regenerative - injector device. But this type of equipment allows you to restore the gas composition in a suit at all stages of a dive. An injector device that operates in two modes, and regenerative box is equipped with two cartridges, which are included in an air recovery system.
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