Radial Bearings

Radial bearings or journal bearings are usually pressure-lubricated. Most compressors use two bearings on opposite ends of the rotor assembly or on the overhung design, located adjacent to each other between the drive coupling and the impeller. It is highly desirable for ease of maintenance to have the bearings horizontally split. On centrifugal compressors, the bearings size is not a function of the load but rather it is dictated by critical speed considerations. Rotors in centrifugal compressors are by nature not very heavy; therefore, the bearings are lightly loaded. Because of the light loading, there are potential bearing-induced rotor dynamics problems.

Straight cylindrical bearings, as shown in Figure 5-36, are the most simple in concept. Because of low resistance to bearing-induced prob-

Figure 5-36. Straight cylindrical bearing. {Courtesy of Turbocare, a Division of DemagDelavel Turbomachinery Corp., Houston facility lems, application of this bearing is limited in centrifugal compressors. It is found normally in very large compressors with relatively heavy rotors and low compressor operating speeds. They are also used in fluorocarbon refrigerant compressors, where speeds are low because of high molecular weight and where relatively short rotors are used, As a minimum, most compressors with sleeve bearings use a modified sleeve bearing, such as the dam type shown in Figure 5-37. A relief groove is cut in the upper half of the bearing. The groove is stopped near the center of the upper portion of the bearing in a square, sharp-edged dam. As the shaft rotates, oil is carried through the groove to the end where the oil velocity is suddenly brought to a halt thereby converting it to pressure. A stabilizing force is formed on the top of the journal by the pressure. The maintenance of the sharp edge at the end of the bearing is very important. In service, if the groove ends become rounded, the bearing will cease to function as intended and can become unstable.

To facilitate maintenance and avoid the tedious scraping and other fitting steps required in early forms of plain journal bearings, replaceable

Figure 5-36. Straight cylindrical bearing. {Courtesy of Turbocare, a Division of DemagDelavel Turbomachinery Corp., Houston facility kwww^

OIL DAM

BEARING LINER (UPPER)

OIL DAM

BEARING LINER (UPPER)

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