Understanding Hydrostatic Bearings

Hydrostatic bearings are designed with an externally pressurized fluid (like oil or air) supplied to the bearing gap. This pressurized fluid creates a film that completely separates the moving surfaces, even when the bearing is stationary or moving at very low speeds.

Starting Friction in Hydrostatic Bearings

Starting friction, also known as static friction, is the resistance encountered when initiating motion between two surfaces. In a hydrostatic bearing:

• The constant supply of pressurized fluid maintains a separating film between the shaft and the bearing surface.
• This fluid film prevents direct metal-to-metal contact, which is the primary cause of high starting friction in other bearing types (like plain or rolling element bearings operating under boundary lubrication).
• The primary resistance to motion at startup is the shear stress within the fluid film itself. Since the fluid is supplied externally and the gap is maintained, this viscous shear resistance is typically very low.

Therefore, the starting friction in a hydrostatic bearing is very low.