First called the cylindrical pressure vessel, the diving tank is probably the most important component of your diving equipment. Storing and transporting high pressure gas to the diver is the main and sole purpose of this diving tank. The divers life depends on this piece of equipment as it is the reason for they are able to keep alive and breathe underwater. The demand valve of the diving regulator is where the gas comes through and this is the part that the diver puts in their mouth. 80cu. ft. is the common measurement for dive tanks which most average adults use. Teens and petite women may use other smaller sized scuba tanks depending on their fitness, lung size, and other health factors.