Publisher Summary This chapter aims to cover all nonfiltration forms of mechanical separation. The achievement of a separation of two or more distinct phases—what is termed mechanical or physical separation (although neither word is precisely descriptive)—can be managed by one of two major technologies: filtration and sedimentation. The division between these two technologies is usually quite clear, although some processes use both together. The theory of sedimentation is entirely concerned with the way in which a particle (or droplet) settles in a continuous fluid. The design of sedimentation equipment is then a matter of giving the particle enough time to settle out of suspension, either to the bottom of the settling tank, or to the nearest solid surface. Of the other types of separators, centrifuges predominate because of the flexibility of their operating principle in adapting to specific process materials, volume and separation requirements, when they may be specifically described by duty such as separators, purifiers, and clarifiers. Cyclones separate solid particles from gases, and hydrocyclones separate the particles from a liquid suspension or separate one liquid from another. These are dynamic separators working on the principle of inertial forces generated by the velocity of the incoming fluid stream. Electrostatic precipitation is an extremely effective method for removing dust, smoke, and other small particles from air or exhaust gases over a particle size range from about 10 μm down to 0.01 μm or even 0.001 μm.