PURPOSE: To prevent the rapid reduction of processing efficiency caused by heat generated in a barrel by providing a fluid filling and evacuating device for the cover of the barrel.

CONSTITUTION: Water is supplied through a water supply pipe 9a and drained through a drain pipe 47a after washing the works contained in a barrel 32a while the barrel 32a is being turned to a tilting position. After washing, a gas is introduced through the water supply pipe 9a to completely drain the washing water remaining in the drain pipe 47a. A hydraulic cylinder 44a lifts up a cover 39a and engages a clutch 62 so that the barrel 32a is tilted downward by a geared motor 60 to throw out the works into a concentrator, then the barrel 32a is raised upright again to load the next works. Subsequently, the hydraulic cylinder 44a lowers the cover 39a and seal the barrel 32a. The water supply pipe 9 and the drain pipe 47a are opening in the barrel 32a to evacuate the gas or liquid from the barrel 32a when the pressure within the barrel exceeded a fixed level.