In order when treating printed circuit boards with liquids, particularly during cleaning, etching, metallizing or rinsing, to achieve a precisely time measurable and effective treatment, the area supplied by means of a spray or swell nozzle or a stationary wave is limited by suction devices (24, 25, 41, 42). The latter are positioned upstream and downstream of the application (28, 38). The spray or suction nozzles (22, 24, 25) are arranged in a common casing and the boards (12) to be treated move horizontally passed its lower periphery.