Abstract: A control valve comprises a valve assembly disposed within a housing and including a valve member movable to open and closed positions with respect to a passageway between the housing inlet and outlet. The valve assembly further includes a plunger reciprocatable within a chamber to an extended position causing the valve member to close the passageway, or to a retracted position permitting the valve member to open the passageway. The control valve further includes a presettable limit member presettable within the chamber to be engaged by the plunger to fix its retracted position, and thereby to preset the magnitude of reciprocatory movement of the plunger and the cross-sectional area of the passageway when the valve member is in its open position.