A dual valve system for a gas turbine engine comprising: a first valve body ; a first valve disc operably disposed within the first valve body, the first valve disc having a first disc geometry; a second valve body ; a second valve disc operably disposed within the second valve body, the second valve disc having a second disc geometry; and a mechanical linkage operably coupled to the first valve disc and the second valve disc; wherein the first disc geometry comprises a substantially uniform thickness (T1) of the first valve disc ; characterized in that : the second disc geometry comprises a tapered thickness (T2) increasing radially outward from a pivot point of the second valve disc ; a first outer edge of the first valve disc forming a first flow area between the first valve body and the first valve disc has a first thickness (T1) that is less than a second thickness (T2) of a second outer edge of the second valve disc forming a second flow area between the second valve body and the second valve disc; the second valve disc has a partially spherical outer diameter; and the second disc geometry differs from the first disc geometry such that opening of the first flow area between the first valve body and the first valve disc occurs prior to opening of the second flow area between the second valve body and the second valve disc responsive to movement of the mechanical linkage. a first valve body ; a first valve disc operably disposed within the first valve body, the first valve disc having a first disc geometry; a second valve body ; a second valve disc operably disposed within the second valve body, the second valve disc having a second disc geometry; and a mechanical linkage operably coupled to the first valve disc and the second valve disc; wherein the first disc geometry comprises a substantially uniform thickness (T1) of the first valve disc ; characterized in that : the second disc geometry comprises a tapered thickness (T2) increasing radially outward from a pivot point of the second valve disc ; a first outer edge of the first valve disc forming a first flow area between the first valve body and the first valve disc has a first thickness (T1) that is less than a second thickness (T2) of a second outer edge of the second valve disc forming a second flow area between the second valve body and the second valve disc; the second valve disc has a partially spherical outer diameter; and the second disc geometry differs from the first disc geometry such that opening of the first flow area between the first valve body and the first valve disc occurs prior to opening of the second flow area between the second valve body and the second valve disc responsive to movement of the mechanical linkage. the second disc geometry comprises a tapered thickness (T2) increasing radially outward from a pivot point of the second valve disc ; a first outer edge of the first valve disc forming a first flow area between the first valve body and the first valve disc has a first thickness (T1) that is less than a second thickness (T2) of a second outer edge of the second valve disc forming a second flow area between the second valve body and the second valve disc; the second valve disc has a partially spherical outer diameter; and the second disc geometry differs from the first disc geometry such that opening of the first flow area between the first valve body and the first valve disc occurs prior to opening of the second flow area between the second valve body and the second valve disc responsive to movement of the mechanical linkage. <EOS>