Apparatus for leading off air in connection with the measuring of the flow of a liquid

For use in a closed-circuit pressurized conduit system through which blood is pumped from a patient through an artificial kidney or like treatment apparatus and returned to the patient, an apparatus for leading off air and preventing the build-up of air pressure in the system and for measuring the flow of blood through the system, said apparatus comprising an inlet chamber and an outlet chamber, inlet means adapted to be connected in the conduit system for directing the blood being pumped therethrough into said inlet chamber and outlet means adapted to be connected in the conduit system for directing blood from said outlet chamber into the conduit system, orifice means in the bottom portion of said inlet chamber providing a flow path from said inlet chamber into said outlet chamber, normally open vent means for venting said outlet chamber to atmosphere, said vent means including valve means operable between an open and a closed position, valve actuating means responsive to the level of blood in one of said chambers for moving said valve means to the closed position to permit build up of system pressure in said outlet chamber and to move said valve to the open position to vent said second chamber to atmosphere upon the blood level in said one chamber dropping below a predetermined level, and blood level measuring means carried by said inlet chamber indicating the level of blood above said orifice means and thereby providing a visible flow rate indication.