A fluid flow control device comprising: a valve body defining an inlet, an outlet, a fluid flow path extending between the inlet and the outlet, and a longitudinal axis, the valve body having a first thermal expansion coefficient; a valve seat disposed within the valve body and defining an orifice through which the fluid flow path passes; a valve cage coupled to the valve seat within the valve body and defining an interior bore, the cage having a second thermal expansion coefficient different than the first thermal expansion coefficient; a valve plug sized for insertion into the interior bore of the valve cage and movable along the longitudinal axis between a closed position, in which the valve plug engages the valve seat, and an open position; a sealing assembly disposed within the fluid flow control device to affect a seal between the valve cage and the valve body, characterized in that the sealing assembly has a biasing element (272e, f) and a sealing portion (272a-d) disposed adjacent to the biasing element, the sealing portion having a thermal expansion coefficient equal to the first or second thermal expansion coefficient, the sealing assembly being arranged in a first compression state in which the biasing element applies a first radial compression force to the sealing portion to bias the sealing portion toward the valve body, the sealing assembly movable to a second compression state in which the biasing element applies a second radial compression force, greater than the first radial compression force, to the sealing portion to bias the sealing portion toward the valve body, the movement of the sealing assembly being due to differential thermal expansion between the valve body and the valve cage in a direction parallel to the longitudinal axis and in a direction transverse to the longitudinal axis. a valve body defining an inlet, an outlet, a fluid flow path extending between the inlet and the outlet, and a longitudinal axis, the valve body having a first thermal expansion coefficient; a valve seat disposed within the valve body and defining an orifice through which the fluid flow path passes; a valve cage coupled to the valve seat within the valve body and defining an interior bore, the cage having a second thermal expansion coefficient different than the first thermal expansion coefficient; a valve plug sized for insertion into the interior bore of the valve cage and movable along the longitudinal axis between a closed position, in which the valve plug engages the valve seat, and an open position; a sealing assembly disposed within the fluid flow control device to affect a seal between the valve cage and the valve body, characterized in that the sealing assembly has a biasing element (272e, f) and a sealing portion (272a-d) disposed adjacent to the biasing element, the sealing portion having a thermal expansion coefficient equal to the first or second thermal expansion coefficient, the sealing assembly being arranged in a first compression state in which the biasing element applies a first radial compression force to the sealing portion to bias the sealing portion toward the valve body, the sealing assembly movable to a second compression state in which the biasing element applies a second radial compression force, greater than the first radial compression force, to the sealing portion to bias the sealing portion toward the valve body, the movement of the sealing assembly being due to differential thermal expansion between the valve body and the valve cage in a direction parallel to the longitudinal axis and in a direction transverse to the longitudinal axis.