PRINCIPLES OF NAVAL ENGINEERING 



practice, since it introduces more excess air 

 than is required for the combustion of the fuel. 



Forced Draft Blower Maintenance 



Forced draft blowers require relatively little 

 maintenance and repair, provided they are 

 operated and maintained in strict accordance 

 with instructions given in the manufacturer's 

 technical manual. A good deal of the mainte- 

 nance work required in connection with blowers 

 is related to keeping the lubrication system in 

 proper condition. All maintenance of blowers 

 must be performed in accordance with the re- 

 quirements of the 3-M System. 



The lubricating oil in the reservoir must be 

 kept clean. The reservoir must always be 

 filled to the correct level with oil of the speci- 

 fied weight and grade. Oil samples must be 

 taken routinely at the specified intervals, or 

 more often if you have reason to suspect that 

 the oil is contaminated. When a sample shows 

 an unusual amount of sediment or water, this 

 fact should be reported to the engineering of- 

 ficer or to the PO in charge, who may issue 

 instructions to change the oil. After the oil 

 has been drained, the inside of the reservoir 

 should be wiped clean. 



The metal-edge type of filter should be 

 cleaned at least once each watch. This is done 

 by giving the handle one or two complete turns. 

 From time to time the filter should be dis- 

 mantled and cleaned; this should be done when- 

 ever the oil is changed in the reservoir, and 

 more often if necessary. 



A common occurrence with vertical blowers 

 is contamination of the oil with fresh water. 

 This happens in an idle blower when leaking 

 steam enters the turbine casing, passes through 

 the upper labyrinth seal, and impinges on the 

 oil slinger, where it condenses and mixes with 

 the oil. This problem can be avoided by keeping 

 the steam valves (especially the exhaust -relief 

 valve) in good repair. If the valves leak, the 

 turbine casing drain of an idle blower must be 

 kept open. 



Automatic shutters are not subject to any 

 great amount of wear under normal operating 

 conditions. However, they must be kept well 

 lubricated at all times. Some types of shutters 

 have Zerk-type grease fittings; others have oil 

 holes. Be sure to use the correct lubricant. 

 K the automatic shutters are not properly lu- 

 bricated, they may stick in the open position 

 and then slam shut with sufficient force to cause 



damage to the shutters and to the toggle gear. 

 Broken or sprung parts must be replaced in 

 order to ensure smooth operation of the shut- 

 ters. Shutters should be inspected frequently 

 to determine whether the leaves operate freely 

 and to be sure that they seal tightly when closed. 



Forced draft blowers should not be operated 

 if they are vibrating excessively or making any 

 unusual noise. Vibration may be caused by worn 

 or loose bearings, a bent shaft, loose or broken 

 foundation bolts or rivets, an unbalanced fan, or 

 other defects. All defects should be corrected 

 as soon as possible in order to prevent a com- 

 plete breakdown of the blower. 



Minor repairs to blower fan blades may be 

 made aboard ship in case of emergency, in ac- 

 cordance with procedures specified in chapter 

 9530 of the Naval Ships Technical Manual. Major 

 repairs to fan blades must NOT be made with- 

 out specific instructions from the Naval Ship 

 Systems Command. As a matter of routine care, 

 blower fan blades should be wiped down from 

 time to time to remove dirt and dust. (One 

 rapid method of cleaning the blades of a multi- 

 stage blower without any disassembly is dis- 

 cussed in chapter 9530 of the Naval Ships Tech- 

 nical Manual .) Paint must NEVER be applied to 

 a blower fan or to any other rotating part of the 

 unit. 



When inspecting and repairing blowers 

 equipped with anti-reverse rotation devices, be 

 careful not to apply reverse torque to the shaft, 

 since this could cause damage to the shaft of 

 the anti-reverse rotation device. 



Safety Precautions 



Some of the most important safety precau- 

 tions to be observed in connection with forced 

 draft blowers are: 



1. Before starting a blower, always make 

 sure that the fan is free of dirt, tools, rags, and 

 other foreign objects or materials. Check the 

 blower room for loose objects that might be 

 drawn into the fan when the blower is started. 



2. Do not try to move automatic shutters by 

 hand if another blower serving the same boiler 

 is already in operation. 



3. When only one blower on a boiler is to 

 be operated, make sure that the automatic shut- 

 ters on the idle blower are closed and locked. 



4. Never try to turn a blower by hand when 

 steam is being admitted to the unit. 



420 



