Patent ID: 7338475

Claim:
An automatic shut off valve for use in regulating the flow of medical fluid from a medical fluid source, comprising: a container configured to operate in an upright position and to contain a varying level of medical fluid received from the medial fluid source and an amount of air above the received medical fluid, the container having an upstream end, a downstream end disposed below the upstream end, and an exit orifice formed at the downstream end through which the medical fluid exits the container, the upstream end and the exit orifice configured so that the received medical fluid will fill the container to a normal operating fluid level during the time that the medical fluid source contains medical fluid, and further configured so that the medical fluid in the container will decrease below the normal operating level during the time that the medical fluid source contains no further medical fluid; a valve seat disposed adjacent the exit orifice at the downstream end of the container and formed of a non-magnetic and dielectric material; and a stop member disposed and freely movable within the container having a buoyancy with which the stop member floats at the surface of the medical fluid in the container, the stop member being spaced apart from the valve seat when the medical fluid in the container has the normal operating level, the stop member formed of a non-magnetic and dielectric material; wherein at least one of the stop member and the valve seat comprises an electrical charge creating an electric field that attracts the other of the stop member and the valve seat and tends to move the stop member into sealing engagement with the valve seat to seal against fluid flow through the exit orifice; wherein the electric field has a strength selected such that, when the medical fluid in the container reaches a selected level that is more than empty but less than the normal operating level, the electric field overcomes the buoyancy of the stop member to move the stop member into sealing engagement with the valve seat, thereby preventing air above the medical fluid from flowing through the exit orifice.