A needle-free adaptor for removing liquid from a vial comprises a cannula adapted to piece a septum of a vial, a plurality of legs surrounding the cannula to secure the adaptor to the vial when the cannula has pieced the septum, an elastomeric membrane having a normally closed pinhole orifice, and a conforming surface having an orifice connected to the cannula. The elastomeric membrane has a stable convex shape and is adapted to receive a nozzle of a needle-free device. Pressed against the elastomeric membrane, the nozzle deflects the elastomeric membrane from the convex shape to an unstable or pseudo-stable inverted position against the conforming surface. Buckling of the elastomeric membrane opens the pinhole orifice and enables fluid communication between the vial and the nozzle by interfacing the pinhole orifice with the orifice on the conforming surface.