Trocar assembly with obturator

A trocar (10) adapted to extend across the body wall into a body cavity, forming a seal around an instrument inserted through the trocar, comprises a cannula (12) having a first axis extending between proximal (16) and distal (14) ends. A valve housing (23) attached to the proximal end of the cannula forms a working channel with the cannula and includes a rigid housing portion (25) and a flexible housing portion (27). First and second septum valves are formed in an end wall of the flexible housing portion and form separate valve sets with associated zero closure valves disposed within the valve housing. The valve sets (52-56) are sized and configured accommodating different ranges of instrument diameters. The first and second septum valves are offset from the axis of the cannula in normal positions but are movable to positions more aligned with the axis of the cannula, due to elastomeric characteristics of the flexible housing.