Abstract: A flow line valve containing an articulated disc, operated by means of a lever actuating mechanism and articulated by the combination of a guide with a rack and pinion gearing system, is disclosed. A valve disc is mounted in a valve body and is operated by rotary motion applied to a crankshaft, through a crank lever and a linking means, which in turn exerts a linear force on the valve disc. The valve disc is initially moved in relation to the seat in a longitudinal direction, directed by a guide means, which is then translated into a pivotation of the disc controlled by a rack and pinion system, such that the valve disc is first longitudinally retracted from the valve seat and then pivoted, clear of the valve seat, 90.degree. to an open position, concurrent with further retraction of the valve seat. Closure is effected by reversing the sequence of articulation.