How a Pusher Centrifuge Works

A pusher centrifuge separates fast-draining solids from liquid continuously, without the stop-start batch cycle of a basket or peeler. Feed slurry enters and lands on the inside of a rotating cylindrical screen. Centrifugal force drives the liquid through the screen while the solids are held back and form a cake against the screen wall.

Instead of letting the cake sit until a batch is unloaded, a pusher moves it. A reciprocating pusher plate strokes back and forth along the axis of the basket, shoving the cake a short distance toward the open discharge end with every stroke. Fresh feed fills the space behind it, so the cake advances as a continuous ring that is washed, dried, and discharged as it travels.

In a single-stage pusher, one basket and one pusher plate move the cake the full length of the screen. In a multi-stage pusher, the cake is transferred across two or more concentric or stepped baskets of increasing diameter. Each stage gives the cake room to spread and drain again, which improves dewatering and handles a longer residence time without an excessively long single basket.

Along the cake's travel there are usually zones for washing and drying. A wash liquid can be applied partway along to displace impurities, and the remaining screen length lets the cake dry before it reaches the discharge. The result is a continuous stream of washed, dewatered solids leaving the open end of the machine.

Pusher centrifuges work best on feeds that drain quickly and form a stable, permeable cake, typically coarse crystals and granular solids at moderate to high solids concentration. Common duties include salt, sodium chloride and other crystalline chemicals, plastics, and mineral products.

They are less suited to fine, slow-draining, or compressible solids, which blind the screen and will not convey cleanly. The feed also needs enough solids to build a supporting cake; too dilute a feed lets liquid and fines slip through to the discharge. Matching the machine to the feed is central to reliable pusher operation.

The screen is the heart of a pusher and takes constant abrasion and pressure; it blinds, wears thin, and eventually needs replacement. The pusher mechanism, including the hydraulic drive, pusher plate, and seals, does heavy repetitive work and is a primary wear and repair item.

Main bearings, the drive, and the feed distributor also wear, and the rotating assembly must stay in balance at high speed. Symptoms of trouble include poor cake conveying, wet or fines-laden discharge, and vibration. A rebuild generally addresses the screen, the pusher and its drive, bearings, and seals, followed by balancing and a test run.