An air separator (1) comprises a first chamber (2) where blood or other fluid can be received, an inlet and an outlet port associated to the bottom wall (4) and in fluid communication with the first chamber. A first channel (14) extending along the lateral wall of the separator and has a first and a second portion (16 and 18). The channel second portion (18) terminally forms an orifice (15) facing the chamber and extending in an area closer to a top wall (5) of the chamber (2) than to the bottom wall of the same chamber. The orifice faces the top of the separator and has a flow passage cross section greater than that of a first portion (16) of the channel.