"Bump washer" probably refers to a crude non-pad, annular thrust bearing which is intended to react transient-only reversed thrust loads on the rotor shaft. They are sometimes called "thrust washers" or "thrust bumpers". On vertically-mounted motors with fluid film bearings, the main thrust bearing may be either dual-directional or uni-directional. For the latter type, it may be necessary to provide a thrust bumper on the thrust runner side opposite the bearing loading side. Metal to metal thrust bumper contact may be allowable if contact load and shaft rotational speed are sufficiently low. Otherwise the thrust bumper surface should be a bearing material such as carbon-graphite, plastic or dense fabric and may be an insert into the contacted metal component. Thrust bumper thrust load endurance capabilities can be enhanced by using equally spaced grooving to introduce several "pads" into the load surface or by special surface contouring like Rayleigh step configurations.
