Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGpractice, since it introduces more excess airthan is required for the combustion of the fuel.Forced Draft Blower MaintenanceForced draft blowers require relatively littlemaintenance and repair, provided they areoperated and maintained in strict accordancewith instructions given in the manufacturer'stechnical manual. A good deal of the maintenancework required in connection with blowersis related to keeping the lubrication system inproper condition. All maintenance of blowersmust be performed in accordance with the requirementsof the 3-M System.The lubricating oil in the reservoir must bekept clean. The reservoir must always befilled to the correct level with oil of the specifiedweight and grade. Oil samples must betaken routinely at the specified intervals, ormore often if you have reason to suspect thatthe oil is contaminated. When a sample showsan unusual amount of sediment or water, thisfact should be reported to the engineering officeror to the PO in charge, who may issueinstructions to change the oil. After the oilhas been drained, the inside of the reservoirshould be wiped clean.The metal-edge type of filter should becleaned at least once each watch. This is doneby giving the handle one or two complete turns.From time to time the filter should be dismantledand cleaned; this should be done wheneverthe oil is changed in the reservoir, andmore often if necessary.A common occurrence with vertical blowersis contamination of the oil with fresh water.This happens in an idle blower when leakingsteam enters the turbine casing, passes throughthe upper labyrinth seal, and impinges on theoil slinger, where it condenses and mixes withthe oil.This problem can be avoided by keepingthe steam valves (especially the exhaust -reliefvalve) in good repair. If the valves leak, theturbine casing drain of an idle blower must bekept open.Automatic shutters are not subject to anygreat amount of wear under normal operatingconditions. However, they must be kept welllubricated at all times. Some types of shuttershave Zerk-type grease fittings; others have oilholes. Be sure to use the correct lubricant.K the automatic shutters are not properly lubricated,they may stick in the open positionand then slam shut with sufficient force to causedamage to the shutters and to the toggle gear.Broken or sprung parts must be replaced inorder to ensure smooth operation of the shutters.Shutters should be inspected frequentlyto determine whether the leaves operate freelyand to be sure that they seal tightly when closed.Forced draft blowers should not be operatedif they are vibrating excessively or making anyunusual noise. Vibration may be caused by wornor loose bearings, a bent shaft, loose or brokenfoundation bolts or rivets, an unbalanced fan, orother defects. All defects should be correctedas soon as possible in order to prevent a completebreakdown of the blower.Minor repairs to blower fan blades may bemade aboard ship in case of emergency, in accordancewith procedures specified in chapter9530 of the Naval Ships Technical Manual. Majorrepairs to fan blades must NOT be made withoutspecific instructions from the Naval ShipSystems Command. As a matter of routine care,blower fan blades should be wiped down fromtime to time to remove dirt and dust. (Onerapid method of cleaning the blades of a multistageblower without any disassembly is discussedin chapter 9530 of the Naval Ships TechnicalManual .) Paint must NEVER be applied toa blower fan or to any other rotating part of theunit.When inspecting and repairing blowersequipped with anti-reverse rotation devices, becareful not to apply reverse torque to the shaft,since this could cause damage to the shaft ofthe anti-reverse rotation device.Safety PrecautionsSome of the most important safety precautionsto be observed in connection with forceddraft blowers are:1. Before starting a blower, always makesure that the fan is free of dirt, tools, rags, andother foreign objects or materials. Check theblower room for loose objects that might bedrawn into the fan when the blower is started.2. Do not try to move automatic shutters byhand if another blower serving the same boileris already in operation.3. When only one blower on a boiler is tobe operated, make sure that the automatic shutterson the idle blower are closed and locked.4. Never try to turn a blower by hand whensteam is being admitted to the unit.420