A system for controlling fluid flow in a closed IV catheter assembly, comprising: a Y-adapter having a straight portion and a Y portion, the straight portion and the Y portion being connected to an IV line; the straight portion includes a blood control valve within an inner lumen of the straight portion, the blood control valve comprising: a septum disposed within the inner lumen of the straight portion;; characterized in that a septum activator is disposed within a portion of the inner lumen of the straight portion adjacent to the septum, a distal end of the septum activator contacting a proximal surface of the septum, and a ventilation channel is interposed between the septum and an inner surface of the inner lumen of the straight portion, the ventilation channel having a surface area and a perimeter selected to permit passage of air at a desired rate of flow; the ventilation channel allows air flow, but prevents blood flow in an unactuated position of the blood control valve in which the septum is closed, wherein blood is therefore permitted to flow into the IV line until it reaches septum, at which point the blood flow ceases, further comprising a lumen forming a fluid pathway through the septum activator, the lumen having an inner diameter configured to permit passage of air, and the septum activator comprises a plurality of flow deflectors configured to improve circulation of the fluid within at least one of the septum activator and an interstitial space between the septum activator and the inner surface of the inner lumen of the straight portion. a Y-adapter having a straight portion and a Y portion, the straight portion and the Y portion being connected to an IV line; the straight portion includes a blood control valve within an inner lumen of the straight portion, the blood control valve comprising: a septum disposed within the inner lumen of the straight portion;; characterized in that a septum activator is disposed within a portion of the inner lumen of the straight portion adjacent to the septum, a distal end of the septum activator contacting a proximal surface of the septum, and a ventilation channel is interposed between the septum and an inner surface of the inner lumen of the straight portion, the ventilation channel having a surface area and a perimeter selected to permit passage of air at a desired rate of flow; a septum disposed within the inner lumen of the straight portion;; characterized in that a septum activator is disposed within a portion of the inner lumen of the straight portion adjacent to the septum, a distal end of the septum activator contacting a proximal surface of the septum, and a ventilation channel is interposed between the septum and an inner surface of the inner lumen of the straight portion, the ventilation channel having a surface area and a perimeter selected to permit passage of air at a desired rate of flow; the ventilation channel allows air flow, but prevents blood flow in an unactuated position of the blood control valve in which the septum is closed, wherein blood is therefore permitted to flow into the IV line until it reaches septum, at which point the blood flow ceases, further comprising a lumen forming a fluid pathway through the septum activator, the lumen having an inner diameter configured to permit passage of air, and the septum activator comprises a plurality of flow deflectors configured to improve circulation of the fluid within at least one of the septum activator and an interstitial space between the septum activator and the inner surface of the inner lumen of the straight portion.