A surgical access device includes a single valve that forms a seal with a body wall and provides an access channel into a body cavity. The valve has properties for creating a zero seal in the absence of an instrument as well as an instrument seal for an instrument having a diameter up to about 37 mm....http://www.google.es/patents/US20070151566?utm_source=gb-gplus-sharePatente US20070151566 - SURGICAL INSTRUMENT ACCESS DEVICE
