The modern thrust bearing is a very important part of the waterwheel generator, for it must support the weight of the rotating parts of the turbine and generator and the hydraulic thrust load. With the continuous increase in size of hydroelectric generating units, machines now are built with thrust loads well above 1000 tons and requiring bearings ten feet in diameter or larger. Continuous trouble-free operationfor periods of twenty years or more are desiredfor the bearings of large hydroelectric units.Except during the starting period, the pivoted pad thrust bearing operates according to the well-known hydrodynamic theory of lubrication which permits the predetermination of its performance with reasonableaccuracy. Alternating slipping between the thrust bearing runner and~he supporting structure can result in excessive wear which destroy the accuracy of the bearing surfaces. Such wear can cause undesirable vibrations or damage to the bearing surface which prevents the formation of an adequate oil film. As a result of laboratory tests and experience in the field, it is now possible to make large thrust bearings with a supporting structure which will permit them to operate continuouslyfor longperiods oftime with practically no wear or loss of adequacy.