NAUI Master Scuba Diver 4 Diving Equipment LEARNING GOALS In this chapter, you will: 1. Learn about the equipment terms presented in bold letters. 2. Learn about the basic types, theories of operation, care, and maintenance of the various items of equipment discussed in this chapter. 3. Read about the items that may be displayed on a dive computer. 4. Learn about the theory of operation of a breathing air compressor; high-pressure, low-volume compressors, and low-pressure high-volume compressors; and how compressors are rated. 5. Read about the primary components of an air or other breathing gas fill station. TYPES OF SCUBA EQUIPMENT There are three categories of Self-Contained Underwater Breathing Apparatus (SCUBA): Open- circuit demand, semi-closed-circuit and closed-circuit. Open-circuit demand scuba is the most commonly used by recreational divers, but closed-circuit and semi-closed rebreathers are now available. A scuba system where the breathing gas is inhaled upon demand from the breathing apparatus and exhaled directly into the water is called open-circuit demand scuba. Closedcircuit scuba units, often referred to as “rebreathers,” are complex systems that remove CO2 from exhaled breathing gas and add oxygen as needed. They are unique in that they do not give off bubbles underwater. Semi-closed scuba recycles part of each exhaled breath while allowing some gas to escape into the water. Semi-closed or closed-circuit scuba equipment has been used in the past by specially trained military and scientific divers, but now is beginning to be used by recreational divers. SCUBA CYLINDERS Scuba cylinders are made of steel or aluminum, and there are different metal alloys of each type. They are manufactured in different physical dimensions and capacities. Although aluminum is a lighter material, steel cylinders can have thinner walls because steel is a stronger material. The following chart (table 1-1) lists the specifications for the many popular sizes. In the U.S., scuba cylinders range in capacity from very small “backup” cylinders or “pony bottles” to well over 100 cubic feet. Cylinders prepared for enriched air nitrox and other breathing gases are also available. Every high-pressure cylinder has markings stamped into the metal on its shoulder that provide valuable information for those who use and service cylinders. These stamped codes reveal the cylinder’s material, capacity, service pressure, manufacturer, testing information, etc. Regulations for cylinders and their markings are established by governmental agencies around the world and vary from place to place. There are two general patterns of cylinder nomenclature in use. The first is typified by the system in use in the United States; the second, by the metric system in use in Europe and elsewhere. The primary difference between them is how cylinder capacity is measured. In the U.S., system service pressure is given in pounds per square inch and the stated capacity is the volume of air which the cylinder contains when it is fully charged. In the metric system, service pressure is given in bars and the measured capacity is the actual internal volume of the cylinder (the total air capacity = service pressure times actual volume). U.S./Canadian Cylinder Markings For US/Canada type cylinders the stamped marks include (see figure 1-1 Scuba Cylinder Markings- US/CAN): • Regulating agency: “DOT” for the Department of Transportation. “CTC” for the Canadian Transportation Commission may also appear. Cylinders manufactured prior to 1970 will have the code “ICC” for the Interstate Commerce Commission. • Metal alloy code: “3AA” stands for the specific
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