Peeler centrifuges are batch centrifuges and usually possess perforated filtration bowls in which cloth filters are used. The liquid in the admitted suspension is centrifuged and filtered at high speeds during which the solids form on the cloth filter in the shape of filter cakes. Once they have been spun-dried, these filter cakes are scraped out on a batch basis by peeler knives inserted into the rotating bowl. The solids may be washed before removal. Peeler centrifuges may, for example, be employed to achieve maximum removal of moisture from solids which have to be as pure as possible or with suspensions that cannot be separated by their different densities.
Pusher centrifuges possess filtration bowls equipped with metal screening sheets or slotted sieves. These systems also filter liquids in the centrifugal field and retain solids as filter cakes in the bowls. An oscillating pushing motion transports the cakes out of the bowls. Solids may also be washed with these systems. Pusher centrifuges work continuously and are recommended for large quantities of solids where medium demands are made on the solids' purity and residual moisture.
Worm-screen centrifuges (Conturbex) may be regarded as alternatives to pusher centrifuges. However, these centrifuges discharge solids from the bowls by a method similar to that used with decanter systems, i.e. by using a rotating worm screw . Compared with pusher centrifuges, this type of equipment may be used with lower or fluctuating solid concentrations.
Inverting filter centrifuges separate the solids similarly to peeler centrifuges by filtration in the centrifugal field. However, the solids are not discharged by a peeling knife but by inversion of the cloth filter through the lateral movement of the bowl walls during rotation. The solids are then spun off outwards from the cloth filter. In contrast to peeler centrifuges, solids are discharged completely without any residual layers being left behind. They may primarily be used in the pharmaceuticals industry where relatively low amounts of solids have to be produced with highest levels of purity.
Basket centrifuges – also called vertical centrifuges – possess bowls that rotate around their vertical axis. The separated solids are either manually removed from the top or periodically discharged from the bottom with the help of a hydraulically powered swivelling peeler.
These centrifuges possess cylindrical tubular-shaped bowls usually with small diameters. The bowls' small diameters mean that tubular centrifuges may be used at very high speeds. The separated solids must be removed manually from these centrifuges. Tubular centrifuges are also suitable for separating liquid/liquid mixes.