The invention is directed to improvements in existing liquid hand held spray guns which deliver liquid to a spray nozzle and have fixed or adjustable spray pattern adjustment of the liquid being dispensed from the nozzle. The improvements comprise the addition of a ball valve between the spray gun internal air flow passage and a container of liquid to be sprayed through the nozzle and a venturi assembly which attaches upstream in a series relationship between the pressurized air input to the gun and the source of pressurized air. The venturi assembly is adaptable to substantially all of the liquid spray guns of the type described and when installed reduces the pressure of the pressurized air entering the gun to 10 PSI or less to comply with governmental environmental pollution standards. With the venturi assembly attached to a given liquid spray gun, the ball valve is employed to provide a slight positive pressure to the container of liquid attached to the gun to control the flow of that liquid from the container into the nozzle. The use of the two assemblies together enhances the flow of liquid to the nozzle and provides environmental acceptable pressure standards to the now non-complying existing liquid spray guns.