A medical valve assembly includes a tube extending between proximal and distal tube ends. A plunger plate extends radially from the distal tube end, and a valve housing surrounds the tube and extends between proximal and distal valve housing ends. The valve housing includes a flange extending radially inwardly from the distal valve housing end and disposed in spaced relationship with the plunger plate to define a distance dimension D extending therebetween. An elastomeric seal is compressed between the plunger plate and the flange to establish a closed condition of the medical valve assembly. The elastomeric seal axially moves one of the valve housing and the tube relative to the other when a medical device is inserted into the medical valve assembly to automatically increase the distance dimension and establish an open and sealed condition of the medical valve assembly with the inserted medical valve.