Active retractable seal for turbo machinery and related method

An active retractable seal assembly for use between rotating and non-rotating turbo machinery components including: a plurality of seal rings mounted to the non-rotating component, the seal rings movable toward and away from the rotating component between respective closed and open positions as a function of pressure drop across the seal rings, wherein the seal rings are normally in the open position; and a fluid bypass circuit for directing fluid around one or more of the plurality of seal rings to reduce the pressure drop across the one or more of the seal rings, thereby causing the one or more seal rings to move towards the open position under the action of spring(s) or actuator(s).