A rotor for a gas turbine engine, comprising: a first rotor disk; and an interstage flange that extends in an axial direction from the first rotor disk to a flange end portion, the flange end portion having an axial end surface and first radial outer and inner surfaces (201A, 201B); characterized by: a circumferential groove, formed in the flange end portion and extending axially from the axial end surface toward the first rotor disk; radial outer and inner slots (220A, 220B) are respectively formed in the first radial outer and inner surfaces along the circumferential groove, respectively radially extending through the first radial outer and inner surfaces; and a valve member disposed within the circumferential groove, the valve member being secured within the circumferential groove when the flange end portion is connected to a second rotor disk, when the rotor is rotating below a predetermined speed, the valve member is in a first deflected state, the radial outer and inner slots being unsealed when the valve member is in the first deflected state, and when the rotor is rotating above the predetermined speed, the valve member is in a second deflected state, the radial outer slot being sealed by the valve member when the valve member is in the second deflected state; wherein the valve member is moved/actuated only by centrifugal forces. a first rotor disk; and an interstage flange that extends in an axial direction from the first rotor disk to a flange end portion, the flange end portion having an axial end surface and first radial outer and inner surfaces (201A, 201B); characterized by: a circumferential groove, formed in the flange end portion and extending axially from the axial end surface toward the first rotor disk; radial outer and inner slots (220A, 220B) are respectively formed in the first radial outer and inner surfaces along the circumferential groove, respectively radially extending through the first radial outer and inner surfaces; and a valve member disposed within the circumferential groove, the valve member being secured within the circumferential groove when the flange end portion is connected to a second rotor disk, when the rotor is rotating below a predetermined speed, the valve member is in a first deflected state, the radial outer and inner slots being unsealed when the valve member is in the first deflected state, and when the rotor is rotating above the predetermined speed, the valve member is in a second deflected state, the radial outer slot being sealed by the valve member when the valve member is in the second deflected state; wherein the valve member is moved/actuated only by centrifugal forces. a circumferential groove, formed in the flange end portion and extending axially from the axial end surface toward the first rotor disk; radial outer and inner slots (220A, 220B) are respectively formed in the first radial outer and inner surfaces along the circumferential groove, respectively radially extending through the first radial outer and inner surfaces; and a valve member disposed within the circumferential groove, the valve member being secured within the circumferential groove when the flange end portion is connected to a second rotor disk, when the rotor is rotating below a predetermined speed, the valve member is in a first deflected state, the radial outer and inner slots being unsealed when the valve member is in the first deflected state, and when the rotor is rotating above the predetermined speed, the valve member is in a second deflected state, the radial outer slot being sealed by the valve member when the valve member is in the second deflected state; wherein the valve member is moved/actuated only by centrifugal forces.