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In the fixed bed centrifuges just described, the separated solids form a cake in the basket that is stationary with respect to the basket while filtration is occurring, and the solids then have to be dug out of the basket in some way. In the moving bed centrifuges, on the other hand, the separating cake is continually moving across the surface of the basket, to discharge at the open end. In the fixed bed, the filtration cycle processes of feeding, draining, filtering, washing and dewatering take place
one after the other through the establishing cake, but in the moving bed designs, these processes are happening all the time, but at different parts of the path from feed to discharge. The fixed bed centrifuge is thus a batch filter, while the moving
bed machine is a continuous flow device (or very nearly so).
The basket of the moving bed centrifuge can rotate about a horizontal axis, or a vertical one (open end facing downwards). The closed end of the basket, at which the feed suspension enters, adjoins the drive mechanism, and the whole basket is
enclosed in a casing designed to collect the liquids leaving along the basket, and the solids discharged at its open end, with a suitable baffle separating the two zones. (The casing can be sealed, to allow the centrifuge to work with organic liquids as
the mother liquor, preventing the escape of vapours.) To aid the sliding motion of the separated solids along the surface of the basket, the filter medium is usually a screen made from wedge-wire bars, welded into the shape of a cone or cylinder, with the long side of the bars parallel to the axis of the basket.