Device for separating oil from blowby gas of an internal combustion engine

The purification device of a gas from an internal combustion motor housing comprises: - a transfer wall (3) having a wall portion (12) with at least one narrow opening (14a) of accelerated distribution; - a wall (10) of gas flow deflection, placed behind the wall and defining a transfer surface of impaction and guiding (20); - an auxiliary opening (24) distinct from the narrow opening formed in the transfer wall; and - a valve (15) type bypass movable against a return member (36) and provided for closing the auxiliary opening (24) by a closure member (30) adapted to approach the surface (20), the return member (36) extending in the impaction chamber and having a portion (38) pushing behind the auxiliary opening in case of overpressure upstream of the wall transfer.