Abstract: A control valve utilizing the conventional dual wafer check valve, which check valve has a pair of semicircular plates pivotally mounted about a pivot rod at the adjacent straight edge surfaces thereof. The plates are mounted by hinge brackets that allow initial translational movement of the pivoted edges of the plates before the rotation about the pivot shaft, so as to provide a clearance between the seal and plates at the pivoted edges. A control mechanism simultaneously and continuously controls the rotation of the wafer plates so that each plate rotates in opposite directions but the same arcuate distance. The control mechanism has a pair of levers with one lever pivoted to the rear surface of one of the plates, while their other ends are pivoted together at one end of a linear translational clevis member. The other end of the clevis member is connected to a pivotal cam follower via a lost-motion connection to convert rotary motion to translational motion.