The present invention includes an ambulatory medical fluid delivery system, which may comprise a fluid flow path for communicating between a source and a patient. The system may also comprise a reusable controller, which may be operable to control fluid flow in the path and include a module interface station, and a disposable fluid flow delivery set, which may include a flow control module adapted to be removably received by the module interface station. Such flow control module may include a flow valve which is operably associated with the path. Such valve may be operably controlled by the reusable controller in response to sensed flow rates of fluid flow in such path. The present invention may alternatively include an ambulatory reusable controller that is provided for use with a disposable medical fluid flow delivery set. The present invention may further alternatively include a differential pressure sensing device.