A flow control system includes a drip chamber having lower and upper wall sections and a collapsible wall extending between the lower and upper wall sections, a downwardly depending valve seat attached to the lower wall section, and a valve member disposed in the drip chamber, attached to the upper wall section and having a valve surface engageable with the valve seat. The system also includes a driver rotatably engaged to the lower and upper wall sections. Upon rotation of the driver in a first direction, the collapsible wall of the drip chamber moves between a collapsed condition in which the valve seat is sealingly engaged with the valve surface and an extended condition in which the valve seat is sufficiently spaced from the valve surface to form a flow passageway between the valve surface and the valve seat and permit flow through the opening of the drip chamber.
