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Gearing problems are due to case distortion， improper gear cooling， or high backlash on the gears. Misalignment also is a great contributor to this problem. Gears should be checked for proper fit; in some cases lapping is advised. Care is always needed to prevent lapping compound from entering the lubrication system and bearings. Cooling of the high-speed gears is accomplished by directing a jet of lubrication oil on the gears as they become unmeshed. In very high-speed applications oil should be directed at the casing to reduce thermal distortion of the casing. Coupling problems are

Figure 21-22. The effect of blade failure on compressor blading.
also directly or indirectly caused by improper lubrication or a high level of misalignment. Couplings of the gear type should have a continuous lubrica-tion system rather than be grease-packed. Grease tends to separate at highspeeds; however， new greases being developed may change the whole coup-ling picture. In manycases， gear couplings are being replaced by disc-type couplings. This type of coupling is more forgiving of angular alignment problems and also does not require any type of lubrication. Misalignment problems in the system can often be aggravated by the piping to the system.Pipe stresses can run very high， and the unit willmove， thus causing high misalignments in the system.
Seal problems can give rise to high leakages and thrust problems. The high leakages reduce the efficiency of the unit and can also lead to contamination of the lubricant. Thrust problems arecreated by air leakage pastseals， causing an unbalance of the thrust forces on the system.
The previous problems are some of the more common types encountered on a gas turbine train. Regular and preventive maintenance is the key to asuccessful operation. Problems will arise， but by proper monitoring of theaerothermal and mechanical problems， preventive maintenance can often avert major or catastrophic failures.
77. Gas Turbine Engineering Handbook

8ibliography
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Nakajima，S.， ""Total ProductiveMaintenance，"" ProductivityPress， Inc.
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Appendix

Equivalent Units

Abbreviations. A二angstrom， atm二standard atmosphere， 760mm of Hg at 0 OC， cal二 cal-orie(gram)， cm二centimeter， deg二degree， gal二gallon， U.S.liquid， gm (and g)二gram， gmole二gram-mole， J二joule， kcal二kilocalorie， kg二kilogram， kJ二kilojoule， km二kilometer， kW二kilowatt， 1二liter， lb二avoirdupoispound， m二meter， mi二 mile (U.S.) mm二millimeter， N二newton， oz二avoirdupoisounce， pmole二poundmole， pt二pint， rad二radian， rev二 revo-lution， s二second， ton二short U.S.ton， V二volt， W二 watt. Others are as usual.
　
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