Abstract: Apparatus for producing a fog/spray as a coating medium for articles. The apparatus comprises a trigger actuated gun having an inlet connected to a source of hydraulically pressurized spray fluid, wherein the pressurizing medium and drive source is itself driven by a compressible fluid such as air. The compressible fluid supply line to the drive source has mounted therein a flow sensing valve which actuates an air valve for controlling atomizing air supply to the applicator gun. The atomizing air supply to the applicator gun is coupled into a gun chamber downstream of the spray orifice so that fluid sprayed through the orifice becomes fogged by the pressurized air in the chamber.