A modular cyclonic separator comprises separating tubes each including an air-guiding impeller that is fixed coaxially in an outer tube body and that is formed with spiral channels for causing an airflow, which flows radially into the separating tube, to follow a cyclonic flow pattern through a separating chamber in the separating tube, thereby separating some of solid impurities from the airflow within the separating chamber. Each separating tube is capable of connecting selectively with one or two three-port valves to form a first or second filtration module, in which the airflow passes through a fluid passage in the one three-port valve or one of the two three-port valves prior to entering the separating tube.