Chapter 1- Diving Equipment Diving Equipment 29 Inter-Stage Pressure Gauge 1 2 condensation of most of the moisture. Water collects at the bottom of this “moisture trap,” which requires periodic draining. The air may then pass directly to a fill station or through a manifold system into large storage cylinders, each equipped with a separate shutoff valve. A storage system, sometimes called an “air bank,” allows high pressure air pumped over a relatively long period of time to be used to fill scuba cylinders in a comparatively short period of time. The storage cylinders are charged during periods of low demand, and air from both the storage cylinders and the compressor is used during periods of high demand. One or more filler hoses with cylinder connectors, on-off valves and bleed valves are connected to the storage cylinder bank (figure 1-33). Small, portable compressors are available for filling scuba cylinders at remote locations. Portable compressors are usually rated at about 85 to 150 L/min (3 to 5 CFM) and are similar to larger, fixed position compressors with the exception that storage cylinder banks are not used - cylinders are filled directly from the compressor. Careful positioning of the air intake and faithful maintenance are extremely important for safety when portable compressors are being used. Low-pressure, high-volume compressors are available for surface-supplied diving, often referred to as hookah diving. A standard regulator second stage is attached to a harness that is attached to an air hose leading to the compressor on the surface. Such a compressor usually has a “volume cylinder” on its output to provide a limited emergency supply of air in case the compressor should stop. A backup air supply in the form of scuba cylinders on the surface or a bailout bottle– a small scuba cylinder carried by the diver–should also be used for surface-supplied diving operations. Divers should be trained for diving with an umbilical hose prior to engaging in surface-supplied diving. Intake Filter Cooling Fins A 1 2 1 1 2 2 B C D Non-Toxic Oil Oil-Pump Petcock Drain Expansion Demoisturizer To Final Filter FIGURE 1-32. 4 STAGE COMPRESSOR FIGURE 1-33. CYLINDER FILLING STATION 1 Intake Valve 2 Exhaust Valve A Stage 1 B Stage 2 C Stage 3 D Stage 4
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