Storage Tank Diffuser

Aviation Boatswains Mate F - Aviation theories and other practices
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sure-relief valve (set at 4 psi), a pressure gage, and a portable inertness analyzer connection. A fixed eductor is installed in the cofferdam to remove any seawater or gasoline that might escape from the storage tanks. The eductor is fitted with two suctions: one near the centerline at the forward end of the cofferdam and the other near the centerline at the after end of the cofferdam. The controls for the eductor are located in a watertight box on the pump room deck. Two static-head liquid-level gages, or electronic sensors, are installed in each cofferdam to indicate the presence of leakage into the compartment. One is located on the centerline in the forward end of the cofferdam and the other on the centerline in the after end. This arrangement makes it possible to determine the presence of leakage, regardless of the trim of the ship. Access to the cofferdam is gained through a bolted manhole cover in the pump room deck. Normally, the cofferdam manhole cover is located directly over the outer tank manhole cover. Storage Tank Diffuser The diffuser (fig. 6-6) reduces turbulence when gasoline or seawater enters the storage tanks. Diffusers are mounted on the bottom of the gasoline storage tanks around the end of each sluice pipe and seawater supply riser. They are bolted to clips or brackets that are welded to the bottom of the tank and to the bulkhead. The diffuser is a perforated cylinder with an open bottom, and it has a top plate with an opening for the gasoline or seawater supply pipe. The opening in the top plate is larger than the outside diameter of the supply pipe, which permits the pipe to move with the movement of the ship’s structure. The total area of the perforations in the diffuser is five times that of the area of the supply pipe. Gasoline or water enters the diffuser in a single stream and is broken into smaller streams as it passes through the holes in the cylinder. The distribution of flow over a large area reduces turbulence. Gaging Equipment Two different types of gages are currently used in the gasoline tanks to determine the amount of gasoline within the tanks. These gages are the water- filled, static-head type, and the TLI. Figure 6-6.—MOGAS storage tank diffuser. The water-filled, static-head gasoline gage (figs. 6-7 and 6-8) provides an accurate means of determining the amount of gasoline in the saddle-type storage tanks. It accomplishes this task by sensing the differential created, as the plane of cleavage between Figure 6-7.—Level indicating panel (front view). 6-8

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