PRINCIPLES OF NAVAL ENGINEERING 



TUMINE 

 FIANCE 



47,31X 

 Figure 5-21.— Gear-type flexible coupling. 



properly will give years of satisfactory service. 

 However, a serious casualty to main reduction 

 gears, will either put the ship out of commis- 

 sion or force it to operate at reduced speed. 

 Extensive repairs to the main reduction gear 

 can be very expensive because they usually 

 have to be made at a shipyard. 



Some things are essential for the proper 

 operation of reduction gears. Proper lubrica- 

 tion includes supplying the required amount of 

 oil to the gears and bearings, plus keeping the 

 oil clean and at the proper temperature. Locking 

 and unlocking the shaft must be done in ac- 

 cordance with the manufacturer's instructions. 

 Abnormal noises and vibrations must be inves- 

 tigated and corrective action taken. Gears must 

 be inspected in accordance with the current 

 instructions issued by NavShips, the type com- 

 mander, or other proper authority. Preventive 

 and corrective maintenance must be conducted 

 in accordance with the 3-M System. 



PROPER LUBRICATION.-Lubrication of 

 reduction gears and bearings is of the utmost 

 importance. The correct quantity and quality of 

 lubricating oil must, at all times, be available 

 in the main sump. The oil must be CLEAN; and 

 it must be supplied to the gears and bearings at 

 the pressure and temperature specified by the 

 manufacturer. 



In order to accomplish proper lubrication of 

 gears and bearings, several conditions must be 

 met. The lube oil service pump must deliver the 

 proper discharge pressure. All relief valves in 

 the lube oil system must be set to function at 

 their designed pressure. On most older ships. 



each bearing has a needle valve to control the 

 amount of oil delivered to the bearing. On newer 

 ships, the quantity of oil to each bearing is con- 

 trolled by an orifice in the supply line. The 

 needle valve setting or the orifice opening must 

 be in accordance with the manufacturer's in- 

 structions or the supply of oil will be affected. 

 Too small a quantity of oil will cause the bear- 

 ing to run hot. If too much oil is delivered to 

 the bearing, the excessive pressure may cause 

 the oil to leak at the oil seal rings. Too much 

 oil may also cause a bearing to overheat. 



Lube oil must reach the bearing at the proper 

 temperature. If the oil is too cold, one of the 

 effects is insufficient oil flow for cooling pur- 

 poses. If the oil supply is too hot, some lubri- 

 cating capacity is lost. 



For most main reduction gears, the normal 

 temperature of oil leaving the lube oil cooler 

 should be between 120° F and 130° F. For full 

 power operation, the temperature of the oil 

 leaving the bearings should be between 140° F 

 and 160° F. The maximum TEMPERATURE RISE 

 of oil passing through any gear or bearing, under 

 any operating conditions, should not exceed 50° F; 

 and the final temperature of the oil leaving the 

 gear or bearing should not exceed 180 °F. This 

 temperature rise and limitation may be deter- 

 mined by installed thermometers or resistance 

 temperature elements. 



Cleanliness of lubricating oil cannot be over- 

 stressed. Oil must be free from impurities, such 

 as water, grit, metal, and dirt. Particular care 

 must be taken to clean out metal flakes and dirt 

 when new gears are wearing in or when gears 

 have been opened for inspection. Lint or dirt, if 

 left in the system may clog the oil spray noz- 

 zles. The spray nozzles must be kept open at all 

 times. Spray nozzles must never be altered with- 

 out the authorization of the Naval Ship Systems 

 Command. 



The lube oil strainers perform satisfactorily 

 under normal operating conditions, but they can- 

 not trap particles of metal and dirt which are 

 fine enough to pass through the mesh. These fine 

 particles can become embedded in the bearing 

 metal and cause wear on the bearings and 

 journals. These fine abrasive particles passing 

 through the gear teeth act like a lapping com- 

 pound and remove metal from the teeth. 



LOCKING AND UNLOCKING THE MAIN 

 SHAFT. — In an emergency, or in the event of a 

 casualty to the main propulsion machinery of a 

 turbine-driven ship, it may be necessary to stop 



104 



