Method of operating an expandable chamber with delay valve

A method of operating an expandable chamber formed with a valve opening in a wall of the chamber, which permits the surrounding environment, such as high temperature steam, to enter the chamber is used. A temperature responsive delay valve closes the chamber to capture a quantity of the steam in an autoclave sterilizing cycle. The closing of the valve is delayed until the high temperature steam has been applied for a predetermined time. A later reduction in pressure surrounding the chamber causes the chamber to expand, which provides an indication that an adequate sterilizing cycle has been provided. The expansion force may also be used to permit a container to close at the end of a sterilizing cycle.