Everything to know about SCUBA:
The SCUBA full form is Self-Contained Underwater Breathing Apparatus. Prior to the 1940s, practically all diving was performed while wearing a diving helmet attached to a hose that allowed air from the surface to be pumped to the diver. Then, in 1943, Jacques Cousteau introduced the SCUBA apparatus, a self-contained underwater breathing device. The open-circuit demand system depicted in Figure 44-4 is the type of Self-Contained Underwater Breathing Apparatus. The device is used in more than 99 percent of all recreational and commercial diving. The components of this system are as follows: a first-stage “reducing” valve for lowering the very high pressure from the tanks to a low-pressure level, one or more tanks containing compressed air, or another breathing mixture.
Moreover, a combination inhalation “demand” valve and exhalation valve that permits air to be pulled into the lungs with slight negative pressure of breathing and then alter exhale into the sea at a pressure level slightly positive to the surrounding water pressure and finally a mask and tube system installed with small “dead space”.
The way the demand system works is as follows:
In SCUBA the first-stage reduction valve lowers the pressure coming from the tanks so that the air delivered to the mask is only a few millimeters Hg higher than the water pressure in the immediate area. There is a pause in the flow of the breathing mixture into the mask. The mask’s demand valve, on the other hand, pulls the diaphragm of the valve open with each inspiration, automatically releasing air from the tank into the mask and lungs. The SCUBA full form is Self-Contained Underwater Breathing Apparatus in this manner, the mask only receives the necessary amount of air for inhalation. When the air is exhausted, it cannot be returned to the tank and instead is released into the ocean.