Abstract: A ball valve where a housing with inlet and outlet ports encompasses a ported gate having spherical surfaces and mounted for rotation about an axis perpendicular to one of the ports. A linear spring assembly seals the ported gate and includes a structure supported seal ring contoured to mate with the spherical surface of the gate and mounted by means of an elastomeric cylindrical element responsive to pressure in the housing to control the contact force between the ported gate and the sealing ring, and with an elastomeric seal ring concentric to the axis of rotation.