Process for preparing a polyolefin resin

A method of manufacturing an olefin polymer composition in at least two polymerization reactors connected in series, wherein the polymer slurry formed in a diluent in the first reactor is sent to a hydrocyclone in which are formed and separated, on the one hand, a stream comprising diluent, and, on the other hand, a concentrated suspension in polymer particles. The concentrated suspension is then introduced into the subsequent polymerization reactor.