A separating device that receives via a lower inlet an air flow laden with impurities, namely dust produced by pads of a brake assembly, and makes it possible to separate and collect heavy dust. The housing of the device contains a multi-cyclone cluster, with cyclones distributed annularly and supplied tangentially by a central collector surmounting an axial duct communicating with the inlet. The centrifuged and separated liquid and solid particles are directly collected below the cyclones in a trapping zone around the duct, the cluster forming a transverse barrier connected in a sealed manner to the duct so as to prevent the liquid collected in the trapping zone from rising towards a downstream zone, only gravity discharge orifices of the cyclones allowing the trapping zone to be filled during the operation of the device.