A mixing chamber formed in a chassis outfitted with separate inlet channels for conveying pressurized liquid phase and gaseous phase and an outlet channel linking the mixing chamber with a spray nozzle via a flow tube. A separate cylindrical packing chamber is formed in the chassis, within which packing chamber a rotor with vanes is set, the vanes of which rotor intermittently close the inlet channels of the two phases formed in separate sectors of said packing chamber as demarcated by the rotor vanes, wherein the gaseous phase inlet channel is closed alternately with at least one liquid phase inlet channel conveying liquid phase into the mixing chamber via open inter-vane channels, wherein also the sector of the packing chamber containing the gaseous phase inlet channel is separated from the mixing chamber by a continuous section of a partition that closes off the rotor's inter-vane channels within this sector.