A system for controlling fluid flow in a catheter assembly is disclosed. The system comprises an intravenous catheter assembly with a catheter adapter. The catheter adapter comprises an inner lumen with a septum disposed within a portion of the inner lumen. The septum has a barrier capable of being deformed from a relaxed position to a biased position. The barrier further comprises a slit having a closed configuration and an opened configuration. The slit is in the closed configuration when the barrier is in the relaxed position and in the opened configuration when the barrier is in the biased position. The barrier is configured to be mechanically deformed from the relaxed position to the biased position by a septum actuator that advances against a proximal surface of the barrier without traversing the barrier.