Understanding Hydrostatic Bearings

Hydrostatic bearings are a type of fluid film bearing where the load is supported by a thin layer of pressurized lubricant, typically oil or air. The key characteristic differentiating them from other bearing types is the source of this lubricant pressure.

Analyzing the Options

Let's break down each option in the context of hydrostatic bearings:

• Option 1: The oil film pressure is generated only by the rotation of the journal

  This statement describes hydrodynamic bearings. In hydrodynamic bearings, the motion of the rotating shaft (journal) within the bearing creates a wedge of lubricant, generating pressure sufficient to separate the surfaces. This is not the case for hydrostatic bearings.

• Option 2: The oil film is maintained by supplying oil under pressure

  This is the defining principle of hydrostatic bearings. An external pump supplies the lubricant (like oil) under pressure to the bearing clearances. This pressurized oil creates a stable, high-pressure film that supports the load, even when there is no relative motion between the journal and the bearing. This ensures excellent lubrication and load support from startup to full speed.

• Option 3: No oil film is required in hydrodynamic bearings

  This statement is incorrect. Hydrodynamic bearings fundamentally rely on the formation of an oil film generated by the journal's rotation to prevent direct metal-to-metal contact and support the load.

• Option 4: None of these

  Since Option 2 accurately describes hydrostatic bearings, this option is incorrect.

Conclusion on Hydrostatic Bearings

Hydrostatic bearings rely on an external source, like a pump, to introduce pressurized lubricant. This external pressure is what maintains the oil film and supports the load, making Option 2 the correct description.