In aerostatic bearings, the orifice diameter is a critical parameter that directly influences load capacity and stiffness. Optimizing orifice size requires balancing air flow rate with pressure distribution across the bearing gap. A smaller orifice restricts flow, reducing air consumption but potentially limiting maximum load due to insufficient pressure buildup. Conversely, a larger orifice permits higher flow, which can increase load capacity but may cause excessive air consumption and reduced stiffness at larger gaps.

The optimal orifice size is determined by the bearing geometry, supply pressure, and desired air gap. For a given bearing area, a too-small orifice creates a high pressure drop across the orifice itself, leaving less pressure available to support the load. This results in lower load capacity and poor stiffness. In contrast, a too-large orifice reduces the pressure drop across the orifice, leading to a more uniform but lower average pressure in the bearing clearance, which also reduces load capacity.

Experimental studies show that the best load capacity often occurs when the orifice diameter is sized so that the pressure at the orifice exit is approximately 50-70% of the supply pressure. This condition allows optimal pressure recovery in the recess and maximizes the average bearing pressure. Additionally, multiple orifices distributed around the bearing surface can improve load capacity and stability, but each orifice must be sized carefully to avoid interference.

Designers typically use dimensionless parameters such as orifice area ratio and bearing number to guide selection. Computational fluid dynamics (CFD) simulations are increasingly employed to model the complex flow behavior and optimize orifice size for specific applications. Ultimately, the goal is to achieve a design that delivers high load capacity with minimal air consumption and stable operation across varying loads. Proper orifice sizing remains a key factor in maximizing the performance of air bearings in precision machinery.