If all machines had a uniform weight distribution and no moving horizontal parts, conventional, constant-stiffness, vibration isolators would keep the equipment level.
(Such isolators have force versus deflection curves that are straight lines.) But machinery rarely has its weight evenly distributed and many have heavy components that move horizontally. To really keep machines level requires isolators with stiffness that increases proportionally with the load, such as the Constant Natural Frequency isolators from Advanced Antivibration Components, New Hyde Park, N.Y. (vibrationmounts.com).
The CNF mounts are engineered with internal gaps and supports that increase stiffness as a load is applied. Therefore the natural frequency remains contact despite changes in the load. (The natural frequency of a system is, by definition, proportional to the square root of the ratio of its stiffness to its mass.) These self-leveling mounts, designated Series V10Z24, area available in three sizes: 400 to 1,000 lb, 700 to 1,900 lb, and up to 8,000 lb for nonimpact machines (such as CNC lathes and machining centers) and up to 5,000 lb for impact equipment (such as punch presses).