Abstract: A pressure responsive valve assembly for a sterilization container having a valve opening comprises a valve closure member for closing the opening and a fluid tight plenum chamber including a rigid wall and an opposite movable wall connected to the valve closure member for movement along a common axis therewith. A spring biases the movable wall and valve closure member away from the rigid wall of the plenum chamber. The movable wall has an area comparable to that of the valve closure member and the plenum chamber has a relatively small length-to-diameter ratio so that when the valve closure member is moved to open or close the valve, the resulting movement of the chamber movable wall changes the volume of the plenum chamber by less than 20%.