Abstract: A medical fluid administration system is provided for connection with an intravenous tubing system in fluid communication with a patient. In an exemplary embodiment the system includes a conduit, a housing connected to the conduit, and a piston having a slit received in the housing and displaceable in its entirety along the longitudinal axis of a region of the housing. A contact member is positioned within the housing for engaging the piston when the piston is displaced along the longitudinal axis of the housing and forcibly pressed against the contact member. The contact member and the piston are sized and configured such that the opposing walls of the slit are deflected laterally to open the slit when the piston is forcibly pressed against the contact member, so that when the piston is pressed against the contact member, fluid can flow through the slit in direct contact with the opposing walls and through the conduit.