Abstract: A device for separating particles from a liquid to be treated is disclosed. The device has a cylindrical enclosure with an inlet for creating a swirling flow at its upper end and an annular channel formed by a flow diverter plate leading to a retention chamber at its base. The flow diverter generates an ascending swirling flow of treated liquid which is discharged through an axial outlet tube in the uppermost portion of the enclosure. The flow diverter includes at least one plane central section and means for adjusting its longitudinal position to adjust the annular channel. The axial outlet tube is extended downwardly by a flow adjusting element to create a flow of annular section.