A rotor for a gas turbine engine has: a first rotor disk; an interstage flange that extends from the first rotor disk to a flange end portion that has an axial end surface and first radial outer and inner surfaces; a circumferential groove, formed in the flange end portion and extending from the axial end surface toward the first rotor disk; radial outer and inner slots formed in the first radial outer and inner surfaces along the circumferential groove and extend through the first radial outer and inner surfaces; and a valve member disposed within the circumferential groove and is secured within the circumferential groove when the flange end portion is connected to a second rotor disk, wherein the valve member deflects from rotor rotational speeds to seal or unseal the radial outer slot.