a valve for controlling the flow of fluent plastic material from an injection molding machine to a mold cavity . the valve includes an axially slidable valve pin that interacts with a material outlet to control flow through the valve selectively . the valve pin is actuated by an eccentric cam arrangement that positively drives the valve pin between positions where it is engaged with or disengaged from the material outlet . the cam acts on the valve pin only in an axial direction to avoid wear occasioned by side loads imposed on a valve pin .