The word scuba is short for self contained underwater breathing apparatus, and these initials were first formed in 1939 in the US Navy and referred to that of the US military diver’s rebreather sets. Just like radar, the acronym is so common that it is not capitalized and is instead thought of as being an ordinary word.
The modern scuba diving set consists of two distinct things and these are open-circuit, called aqualung in the European countries and the closed-circuit/semi-closed circuit also known as a rebreather. In the case of aqualung or open-circuit scuba diving gear review, the diver is able to breathe in from the set and out to waste.
This is simple equipment and is easily and cheaply manufactured though it is uneconomical when used with expensive gas mixes like heliox and trimix and most divers just use standard air consisting of 21% oxygen and 79% Nitrogen.
The air mixture is kept under pressure in the air tanks on the diver's back and must ass through a regulator to reduce the air pressure to a level that is safe and comfortable to breathe. It is vital that the air regulator is kept in tip-top condition. Never dive if you have any doubts about the reliability of your equipment and especially the air pressure regulator.