Figure 1: Plain Cylindrical Journal Bearing

Figure 1 shows the plain cylindrical bearing, which is the simplest design of a fixed geometry fluid film bearing. As a review, cross-coupling of a fixed geometry bearing causes displacement of the shaft in the direction of the supporting load from the oil wedge and displacement perpendicular to the direction of the supporting load in the direction of rotation. Cross-coupling leads to the attitude angle of the rotor during operation. The operating position of the bearing, as shown in the figure, causes a region of high pressure which grows in width as the shaft speed is increased. The oil pressure distribution in a plain cylindrical journal bearing can be seen in Figure 2.

Figure 2: Circumferential Oil Film Pressure Distribution at (a) 100 rpm and (b) 3,600 rpm

In the last video, the recommended installation locations on three different styles of fluid film bearings were discussed. On a plain cylindrical journal bearing, two locations were recommended. One sensor should be installed at the bottom dead center of the bearing, while a second sensor can be installed 45° in the direction of rotation for added diagnostic capabilities. Figure 3 shows these two sensors, which were installed at the proper locations with the proper orientations on the bearing.

Figure 3: Voyager FDS Installed Properly

While the location of the mounted sensors is important, the orientation of the sensors is also important. The arrow that points along the length of the sensor's rectangular body denotes the sensor’s measurement direction. When installing the Voyager FDS sensor, this arrow must point towards the center of the shaft to ensure accurate amplitudes are measured.

Figure 4: Voyager FDS Sensor Installed Improperly

Figure 4 shows an example of these two sensors installed improperly on the same bearing. In the figure, it can be seen that the measurement axis of the bottom dead center sensor is not pointing towards the center of the shaft. Additionally, the second sensor is installed at only 30° with rotation from the bottom dead center location, and its measurement axis is not pointing towards the center of the shaft. The improper sensor orientation and position of the sensors will cause inaccurate data to be collected.

Topic of Next Video

Thank you very much for watching this video. The next series of videos will review the procedure to install the Voyager FDS sensor.