Abstract: A valve insert includes an elongated cannula with first and second sharp ends. First and second elongated, flexible, elastomeric covers are respectively disposed over the first and second sharp ends of the cannula. Each cover is secured to an intermediate part of the cannula and is made of a material penetrable by the sharp ends of the cannula as the cannula moves longitudinally relative to the covers. The insert is mounted in an elongated bore through a valve body so that when a hypodermic syringe nozzle is inserted inito one end of the bore, the cannula and covers are displaced longitudinally, causing the sharp ends of the cannula to pierce the covers and open the cannula for fluid flow.