The present invention relates to an air separator (100) for an extracorporeal blood circuit for separating out air from a fluid flowing through the air separator (100), comprising an air separation chamber (1) having at least one inflow passage (9) and at least one outflow passage (25). It further relates to an external functional means, a blood circuit, and a treatment apparatus.本發明有關一種用於體外血液迴路之空氣分離器(100),可從流經空氣分離器(100)的流體分離出空氣,其包括一個空氣分離室(1)。空氣分離室(1)具有至少一個流入通道(9)與至少一個流出通道(25)。本發明進而有關一外部功能性裝置、一血液迴路、及一治療設備。