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In general, antifriction bearings are preferred largely because they: 

• Offer little rotational resistance, 

• Facilitate precision alignment of rotating elements, 

• Are relatively inexpensive, 

• Are easily replaced, 

• Withstand high momentary overloads, 

• Are simple to cool, lubricate, and maintain, 

• Accommodate both radial and axial loads, and 

• Are relatively resistant to elevated temperatures. 

The main disadvantages are their vulnerability to foreign matter and tendency to fail without appreciable warning. 

Usually the ball bearings are positioned on the compressor or turbine shaft so that they can absorb any axial (thrust) loads or radial loads. Because the roller bearings present a larger working surface, they are better equipped to support radial loads than thrust loads. Therefore, they are used primarily for this purpose. A typical ball or roller bearing assembly includes a bearing support housing, which must be strongly constructed and supported in order to carry the radial and axial loads of the rapidly rotating rotor. The bearing housing usually contains oil seals to prevent the oil leaking from its normal path of flow. It also delivers the oil to the bearing for its lubrication, usually through spray nozzles. The oil seals may be the labyrinth or thread (helical) type. These seals also may be pressurized to minimize oil leaking along the compressor shaft. The labyrinth seal is usually pressurized, but the helical seal depends solely on reverse threading to 

