a purifier device for a bleed circuit of a block of an internal combustion engine provided with a filter member acting by coalescence adapted to be traversed by a flow of gases from the interior of the block and containing oil and particulates in suspension ; the filter member has an absolute retaining power such as to allow the passage of the particulates so that they are incorporated on the particles of oil agglomerated by coalescence within the filter member and are removed with this oil without the risk of the filter member becoming clogged up .