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The lubricant of a gear coupling must withstand severe service from forcesin the coupling which exceed .000 g"s. For grease-filled couplings， special-quality grease is required to prevent mating teeth wear while operating at high-g loads in a sliding load environment. This severe operating condition causes grease separation at high speeds and results in excessive wear. Testsindicate that grease separation is a function of g levels and time. Therefore，the grease coupling is not considered suitable for high-speedservice， exceptwhen approved high-speed coupling grease isused， and then only for up toone year of continuous operation. Presently， new greases on the market do not separate at high speeds and may not deteriorate for three years of continuous operation.
The continuous oil-flow method is used primarily in high-speed rotating machinery. This method provides the potential for maximum continuous periods of operation at high operating speeds. The oil flow also provides cooling by carrying away heat generated within the coupling. Anotherimportant advantage is maximum reliability， since the oil supply is constant， and the loss of oil from within the coupling is not a problem as it is with oil-filled or grease-packed couplings. The main requisites for this method are:
(1) provision of adequate oil flow into the coupling， (2) the oil must be

absolutelyclean， and (3) it must cool to carry away heat. Some of the disadvantages of the continuous oil-flow coupling are:

(1) increasedcost， (2) requires supply oil and return oilpiping， and (3) the entry of foreign solids with the oil will cause accelerated wear.

Foreign material in the oil is a ma.or problem with the continous oil-flowcoupling. Since high centrifugal forces are developed within the coupling， any induced solids and water will be extracted from the oil and retained in the coupling. Abrasive wear is usually caused by the trapped sludge. Inaddition to the foreign abrasives， the sludge will retain the wear metal and will contribute to the coupling wear rate. Sludging has been reduced within couplings by improved oil filtration. Filters can be equipped with differential pressure alarms so that replacement can be made.
The gear-type coupling on turbomachinery can be successfully lubricated by both oil and grease methods. The grease-packed and oil-packed couplingsmust be absolutely oil and grease tight to prevent the loss of lubricant， and the very best high-speed coupling grease must be used. The continuous-flow type must have absolutely clean oil supplied continuously at the designed flow rate.
Lubrication Management Program
A well-planned and managed lubrication program is an important factor in the overall maintenance plan of a plant. A lubrication program includesdeveloping a lubrication period maintenance program， sampling and testingoil， and developing specific procedures to apply lubricants. The initial step in developing a comprehensive plant lubrication program is to conduct a plant survey to determine existing lubrication practices. The survey should utilize machine drawings and external machinery inspections.
A detailed list of lubricant types and their points of application can be compiled from the results of the survey. Combining the list of lubricationtypes and a currentschedule， a master plant lubrication schedule can be published.
A monthly lubrication schedule can then be issued to the appropriate maintenance personnel to serve as a reminder. The issuing of the lubricationschedule does not ensure its compliance， and supervisors should check to see that required lubrication is performed.
As a part of the lubrication program， oil should be periodically tested. The testing requires drawing oil from the system for a laboratory analysis. Theusual tests conducted to determine the condition of oils include viscosity， pHand neutralization number， precipitation， color and odor， and a check for foreign particles in the oil. The results should be reviewed and compared with new oil characteristics to determine the life characteristics of the oil.
　
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