A centrifugal separator includes a cylindrical bowl having a conical lower end with an opening through which feed liquid is injected during a feed mode of operation. During the feed mode, solids separate from the feed liquid and accumulate along the inner surface of the bowl as the bowl rotates at high speed. After accumulation of the solids, the rotation of the bowl is stopped and residual liquid is drained by gravity from the bowl. In a solids discharge mode of operation, a piston of a piston assembly is urged downward along a vertical axis in response to fluid such as compressed gas or hydraulic liquid. The downward movement of the piston forces accumulated solids from the bowl via the opening in the conical lower end thereof. The solids pass from the bowl and into a passage leading to an outlet port, where the solids exit the separator.