A double valve seal to prevent escape of liquids or gases through a cannula, the seal having a diaphragm valve with a circular aperture to seal the cannula when an instrument is inserted and a spilt conical valve to seal the cannula when no instrument is present. A pair of diametrically opposed...http://www.google.co.uk/patents/US5727770?utm_source=gb-gplus-sharePatent US5727770 - Double valve cannula seal
