the valve shaft passes through a journal bearing in the wall of the valve body to an actuating lever attached to the shaft on the outside of the valve body . this journal bearing is sealed by an arrangement of several parts to prevent escape of exhaust gases . these parts include a bellows and ceramic thrust washers . by making the valve shaft axis non - perpendicularly intersecting the axis of the valve body wall , the entire circumference of the valve blade can be sealed to the valve body wall when the valve is closed .