Fluid Bearing - Operation

Operation

Fluid bearings use a thin layer of liquid or gas fluid between the bearing faces, typically sealed around or under the rotating shaft.

There are two principal ways of getting the fluid into the bearing:

• In fluid static, hydrostatic and many gas or air bearings, the fluid is pumped in through an orifice or through a porous material.
• In fluid-dynamic bearings, the bearing rotation sucks the fluid on to the inner surface of the bearing, forming a lubricating wedge under or around the shaft.

Hydrostatic bearings rely on an external pump. The power required by that pump contributes to system energy loss just as bearing friction otherwise would. Better seals can reduce leak rates and pumping power, but may increase friction.

Hydrodynamic bearings rely on bearing motion to suck fluid into the bearing and may have high friction and short life at speeds lower than design or during starts and stops. An external pump or secondary bearing may be used for startup and shutdown to prevent damage to the hydrodynamic bearing. A secondary bearing may have high friction and short operating life, but good overall service life if bearing starts and stops are infrequent.