121.33Figure 3-13.—Emergency repair of a tube leak in a radiatortype heat exchanger.should be replaced as soon as a leak develops, ifa replacement is available. The presence of oneleak, unless caused by dropping or accidentalpuncture, indicates that other areas in the heatexchanger may be eroded.In shell-and-tube heat exchangers, a leakingtube must be replaced as soon as possible. In anemergency, a faulty tube may be blocked off byinserting a special plug at each end, until the tubecan be replaced. An air lance or water lanceshould be used to clean the tubes of a shell-and-tube heat exchanger. If the scale has hardened inthe tubes, a round bristle brush or soft rubberplugs may be used to clean the tubes. When clean-ing the tubes by mechanical means, avoiddamaging the protective coating inside the tubes.These tubes should never be polished, as the tar-nish on the tubes acts as insulation to preventChapter 3—ENGINE MAINTENANCEfurther corrosion. Removing the tarnish will alsoreduce the tube wall thickness and over a periodof time and a number of cleanings, could suffi-ciently reduce tube strength, resulting in tubefailure. For the proper procedures for cleaningshell and tube type heat exchangers and thesafety precautions, use the PMS maintenancerequirements cards, the manufacturer’s technicalmanual and Naval Ships’s Technical Manual,chapter 254.LUBRICATING SYSTEMTo ensure that all the parts of an engine receiveadequate lubrication, it is essential that all partsof the lubricating oil system be properly main-tained at all times. Some parts which may be asource of trouble are considered in this section.For other information on lubricating systems, seeEngineman 3 & 2, NAVEDTRA 10541 (currentedition).LUBE OIL PUMPSPumps used in engine lubricating systems areof the positive displacement type. In some pumpspressure control is maintained by pressureregulating or pressure relief valves built directlyinto the pump; in other pumps, valves exteriorto the pump are used for this purpose. Mostregulating devices recirculate excess lube oil backto the suction side of the pump, but some pumpsdischarge excess oil directly into the engine sump.Pump casualties, as well as many other lubesystems failures, are indicated by the loss of lubeoil pressure. The loss of oil pressure can berecognized by checking the pressure gages atprescribed intervals, or by means of an electricalalarm system. Most lube oil pump failures aregenerally due to wear, and develop gradually.Failures may also occur abruptly if a drive shaftbreaks, or some parts suffer physical deforma-tion. Such failures are usually indicated by ab-normal noise in the pump and by sounding of thelow-pressure lube oil alarm.The warning system should be tested atspecified intervals, usually when an engine isbeing started or secured. Warning systems do notexcuse personnel from their responsibility forkeeping a vigilant and accurate watch on engine3-15
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