nickel and carries the fuel. The outer pipe is steel andserves as an armor casing. The outer pipe also servesto contain a protective jacket of inert nitrogen gas at3 psi around the inner piping. A pressure gage for thedouble-walled piping is installed in the pump room toindicate the pressure in the piping. The gage has arange of zero to 15 psi.If the outer casing is pierced, the nitrogen gas willleak out. The resulting drop in pressure will be indicatedon the gage. Also, if a rupture should occur in the fuelline inside the steel casing, the resulting increase inpressure will be indicated on the gage. Isolate the pipinguntil the cause has been determined.Expansion bellows are provided in the outercasing to avoid strains in the casing due to unequalexpansion, which may result in leakage of thenitrogen gas. Drain plugs in the bellows can be usedto determine whether any leaks have occurred in theinner piping. Brass liners soldered to the outside ofthe inner piping and steel spacers welded to theinside of the outer piping are placed at intervals ofabout 5 feet. These serve to hold the inner piping inthe center of the outer piping and still allow formovement caused by expansion and contractionbetween the two pipes. The outside piping is about 2inches larger than the inner piping.An inert gas connection, for charging the outerpiping, is provided at the lower or inboard end of thedouble-walled piping. The outer piping is alsoprovided with a relief valve to avoid excess pressure.The released inert gas is vented to the atmospherethrough separate piping. The relief valve is set at 15psi.AUTOMATIC PRESSURE-REGULATING SYSTEMThe pressure-regulating system (fig. 6-12) used inMOGAS risers is identical for all class ships except forsize and pressure settings. This section deals with atypical regulating system without reference to sizeFigure 6-12.—MOGAS pressure-regulating system.6-12
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