An improved pinch mechanism for a fluid flow control assembly. It comprises a trumpet-type actuator moveable along its principal axis to control flow through an associated resilient tubular member. Interconnected with the actuator is a caming assembly having a roller guide with a principal surface sloping at an acute angle with respect to the actuator principal axis. Engaging with that principal surface is a dog-leg shaped cam follower that is pivoted at one end for partial rotational movement about the pivot. It is spring loaded to normally retain it in a position in which a proximal end of the follower is pressed on a resilient surface of the tubular member to squeeze it closed. Partial rotation of the cam follower occurs when the actuator moves along its principal axis and the cam forces the cam follower to move through an arc that permits the squeezed tubular member to assume its normally unsqueezed and open shape.