Anatomy of the Oil Film

In a hydrostatic support, a high-pressure pump delivers oil through a restrictor into recessed cavities (oil pockets) on one bearing surface. The oil flows across the land (the small gap) to the edge, building a pressure profile that lifts and supports the moving element entirely on a thin film—typically 3–50 μm thick.

Pressure and Load

Supply pressure is normally 1–10 MPa. When an external load presses down, the film on the loaded side thins slightly; the restrictor responds by raising that cavity's pressure, restoring equilibrium. This self-correcting behaviour is what gives hydrostatic systems their remarkable load capacity and stiffness.

Why Thickness Matters

A thicker nominal film tolerates contamination better but reduces stiffness; a thinner film raises stiffness but demands higher oil cleanliness. In practice, design oil-film thickness is 3–10 μm for precision hydrostatic components, with oil-cavity flatness held within ≤0.5 μm so the film stays uniform.

Takeaway

The oil film is not a static cushion—it is an actively controlled pressure field. Proper pressure, clean oil, and precise cavity geometry are what turn a simple film into a precision bearing.