Abstract: A printing apparatus includes a head that faces a medium supported by a medium support unit and ejects a liquid, an interference object sensor including a detector that detects an interference object with the head, and a cover that can switch the detector to a shielded state and to an exposed state.

Abstract: A fluid jet-mixing apparatus for use in a flow deflecting structure or passageway unit disposed intermediately between an inlet and an outlet of a fluid or fluids to and from an adjacent reacting area in the upstream or downstream thereof, which incorporates a guide vane assembly for allowing the fluid or fluids to pass therethrough under appropriate flow velocity and pressure conditions, the guide vane assembly comprising a cylindrical wall member defining the fluid passageway and a flow deflecting structure of a guide vane form disposed within the cylindrical wall member and composed of a plurality of generally semi-elliptic shaped panel members and a triangular-shaped partition member, and a suction or introduction pipe member incorporated concentrically in the center of the guide vane assembly and extending in communication with the outside of the passageway system so as to cause another fluid to be dynamically introduced or sucked from outside into the fluid passageway system, thereby to have the flowing