Abstract: An ultrasonic nozzle includes an atomizing surface for producing an atomized liquid spray, a liquid-feed passageway for supplying process liquid to the atomizing surface, the passageway having a first-diameter section and a second fluidly connected smaller-diameter section, with a shoulder defined therebetween; an internal shut-off assembly for controlling the supply of process liquid to the atomizing surface, the shut-off assembly including a shut-off rod slidably positioned within the passageway and having a sealing end adapted to cooperate with the shoulder, an actuator piston connected with the opposite end of the shut-off rod and slidable within a cylinder bore which is in fluid communication with the passageway, and a valve actuator for slidably moving the piston and shut-off rod in the passageway between a first closed position and a second open position, by which operation the supply of liquid to the atomizing surface is controlled.