Operating Troubles procedures onboard your ship, refer to your ship’s Cargo Fuel Operational Sequencing System (CFOSS) Some operating troubles may be evident from a manuals. low discharge pressure, excessive or unusual noise, or an overloaded driving unit. The following paragraphs discuss the most likely causes of operating troubles. LOW DISCHARGE PRESSURE.— A low dis- charge pressure generally indicates that not enough oil is being pumped. This condition may exist because the pump needs priming or because of leakage. A gradual decrease in discharge pressure over a period of time is generally the result of pumping oil that contains abrasive particles, which causes the housing and rotors to wear. The theories and laws of physics apply to all fuel systems, but you must understand them completely before you attempt to operate a fixed MOGAS sys- tem. U-TUBE PRINCIPLE OF THE MOGAS SYSTEM Hydraulics is the study of the behavior of fluids in their application to engineering problems. The fun- damental law underlying the whole science of hydrau- NOISE.— Excessive or unusual noises may be lics was discovered by the French scientist Pascal, in caused by cold oil, dirty strainers, air in the oil, vapor- the seventeenth century. Pascal’s law states: “Any ization of the oil because of increased temperature, or pressure or force applied to a confined liquid will be misalignment of the coupling. transmitted equally and undiminished in all direc- tions, regardless of the size or shape of the container.” OVERLOADED DRIVING UNIT.— Excessive friction in the pump or in the driving unit can cause a Liquid seeks its own level. The surface of the driving unit to be overloaded. Misalignment of parts water in a teakettle is at the same level in the spout as when the pump is reassembled increases friction. it is in the body of the kettle. This rule also applies Overloading may also be caused by faulty operation when a liquid is introduced to several differently of the system, heavy or cold oil, or from other causes shaped, openly connected tanks. The surface of the that are not due to actual malfunctioning of the pump. liquid would be at the same level in each connected tank. MOGAS SYSTEMS AFLOAT LEARNING OBJECTIVES: Describe the typi- cal afloat MOGAS system. Identify the protec- tive systems for afloat MOGAS components. Explain the correct operating procedures for afloat MOGAS systems. As an ABF assigned to LPD and LHA ships, you will be working with motor gasoline (MOGAS) sys- The two liquids handled in the MOGAS system are seawater and gasoline. A cubic foot of seawater weighs 64.0 pounds, while a cubic foot of gasoline weighs 45.8 pounds. Since gasoline is lighter than seawater, it will float on top of the seawater and not mix with it. A U-tube analogy to the MOGAS system, shown in figure 6-4, is based on two principles: The weight per unit volume of gasoline is less than that of seawater. Therefore, the gasoline will float on the surface of the seawater. tems. As with JP-5 systems, each ship is different, even ships within the same class. As older equipment            A given head of seawater in a U-tube will hold is replaced with newer equipment, the uniformity in balance a greater head of gasoline because the gaso- among ships will increase until firm standardization line is lighter than the seawater. evolves. The MOGAS system on the ship is really a giant Most equipment used in a fixed MOGAS system, U-tube. The saddle storage tank containing seawater such as pumps, valves, and filters are identical to the and gasoline forms the bottom of the tube. The sea- same equipment used in the afloat JP-5 system only water piping forms one side of the tube, and the smaller. This chapter will cover the major areas gasoline piping forms the other side. within a typical fixed MOGAS system aboard an LHA The installation is designed to keep the gasoline and the equipment unique to this system. Other class storage tanks entirely full at all times, either with ship’s systems are slightly different. For specific sys- gasoline on top of the seawater or completely with tem information and operation and maintenance seawater. As gasoline is drawn off, water replaces it, 6-5