Abstract: A barrel assembly for a twin screw mixer or similar device is especially designed for ready access to a replaceable split liquid tight barrel liner which is accurately held in seated position within a housing block by a minimum number of bolts or other detachable connectors. Housing blocks are formed with liner half receiving recesses defined by flat surfaces which include inwardly convergent side walls and a flat inner wall. The liner half is of complementary shape and projects slightly from the recess, when seated in the recess so that closing of the housing blocks engages abutting surfaces on the two liner halves to clamp these surfaces against each other during operation of the machine. The housing blocks are mounted upon the machine frame by brackets for swinging movement about horizontal axes, meshing pinion gears couple the housing blocks to each other so that the weight of one housing block is counterbalanced by the other during opening and closing movements.