NAUI Master Scuba Diver 28 Diving Equipment Thinsulate® and radiant insulating material are both efficient insulators, even when wet. Open cell foam maintains good efficiency when damp but will not keep you warm if your suit floods. “Woolly bears” rapidly lose their heat trapping capabilities when damp. The dry suit and insulation combination worn will determine the amount of weight you will need for diving. The more insulation worn, the more air will be trapped in the suit. In general, most dry suit underwear combinations require some additional weight beyond what you might wear with a full 7 mm (1/4 inch) thick wet suit. Polypropylene liners can be worn next to your skin, beneath the dry suit undergarments. The purpose of the liner is to wick moisture (sweat) away from your body to keep you feeling dry. The liner also serves as an extra bit of insulation in colder waters. Other equipment adaptations must also be made when using a dry suit. Extra large fin pockets are often a necessity with dry suit boots. Back mounted buoyancy systems work better with many dry suit valve configurations. Low pressure swivel “T’s” may be needed on some regulators to accommodate the addition of the dry suit inflator hose. Ankle weights may be used to help distribute additional weight, and to help keep the legs from floating up. Careful selection of all of the components of your dry suit system will give you the greatest comfort, safety, and productivity for cold water diving. AIR COMPRESSORS There are two main types of compressors used in diving: high-pressure, low volume, used to fill scuba cylinders (figure 1-31); and low-pressure, high volume, used for surface-supplied diving. High-pressure, low volume compressors are similar to other types used for industrial purposes except that non-toxic oil must be used for lubrication, and special attention and filtration are required to prevent contamination of the air. A compressor operates on the principle of Boyle’s law – pressure is increased by reducing volume. The air is compressed in stages. The volume of each successive stage in a compressor is smaller in order to achieve an increase in pressure at that particular stage. Air is prevented from returning to a previous stage by the use of one-way “check valves” located between each stage. To protect the machine from damage, each stage is equipped with an overpressure relief valve. Compressors may be driven by either internal combustion or electric motors. Fewer toxins or emissions are produced by an electric motor. Air compressors are rated according to how many liters per minute (LM) cubic feet per minute (CFM) on the average they can pump. If an empty 2300 L (80 cubic foot) capacity cylinder were pumped full in 10 minutes, the rating of the compressor would be 230 L/ min (8 CFM). Air from a compressor usually passes through two or more filters in series (figure 1-32). These filters remove odors and further reduce the humidity of the air, but will not remove carbon monoxide. Air is heated when it is compressed and is able to contain more moisture than when cool. Water is undesirable in scuba cylinders. Air from the final stage of a compressor is usually directed into an expansion chamber, where the expansion reduces the temperature and causes the FIGURE 1-31. SCUBA AIR COMPRESSOR
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