With reference to turbocharger bearings:

White metal sleeve bearings:

Advantages: high load capacity, good damping of vibration, can tolerate some misalignment, long life, and can be re-metalled. They are used on large turbochargers.

Disadvantages: require a continuous oil supply (from the engine lubricating oil system), more complex, and if the oil supply fails they can seize.

Ball race bearings:

Advantages: simple, self-contained (grease or oil lubricated), low friction, no external oil supply needed, and can run at high speed.

Disadvantages: limited load capacity, shorter life (fatigue), sensitive to misalignment and vibration, and cannot be re-metalled (must be replaced).

For large marine turbochargers, white metal sleeve bearings are usually used because of the high load and the availability of the engine oil supply; ball race bearings are used on smaller turbochargers.

The axial location of the turbocharger rotor is achieved by a thrust bearing arrangement. On a turbocharger with white metal sleeve bearings, a thrust collar on the rotor runs against thrust pads (or a thrust bearing) which locate the rotor axially. On a turbocharger with ball race bearings, the ball bearings themselves provide the axial location (one bearing is located axially). The axial location prevents the rotor from moving axially due to the gas forces and the thrust.

The bearings are kept cool by:

1. A continuous supply of lubricating oil (from the engine oil system) which lubricates and cools the bearings; the oil carries away the heat of friction.
2. The oil is cooled in the engine oil cooler before being supplied to the turbocharger.
3. On some turbochargers, the bearing housing is water-cooled (a cooling water jacket) to remove the heat.
4. The oil flow and the temperature are monitored to ensure adequate cooling.

The bearings are sealed from the atmosphere and the exhaust gas by:

1. Labyrinth seals (a series of fine grooves/teeth) on the rotor shaft at the compressor and turbine ends, which restrict the flow of air and gas along the shaft.
2. A small positive pressure of air (or the compressor discharge) in the bearing housing, which prevents the exhaust gas from entering the bearing housing.
3. The oil seals (e.g. a slinger ring and a drain) which prevent the oil from leaking out and prevent the gas from entering.

The seals keep the bearings clean and prevent the hot exhaust gas from reaching the bearings.