Abstract: A medical valve includes a valve body having a central fluid passageway defined therein. A movable piston adapted in size and shape to be located within said central fluid passageway of said valve body. A sealing interface is defined between said movable piston and said central fluid passageway. An upper seal is located at an upper portion of said sealing interface. It is formed by a seal carried by said valve body. A lower seal is located at a lower portion of said sealing interface, and is formed by a seal carried by said movable piston. The lower seal remains intact until after said upper seal is broken.