The present invention provides a sterilizer having a housing defining a sterilization chamber. An opening in the housing communicates with the chamber. A surface surrounds the opening, and a door is movable between one of an open position allowing access to the chamber through the opening and a closed position covering the opening. A seal element is associated with the surface for forming a fluid-tight seal between the door and the surface when the door is in the closed position. An operating system is provided for applying pressure to one side of the seal from a first source external to the operating system to force the seal into engagement with the door. Sensing means are provided for monitoring the pressure applied to the seal from the first pressure source. A second source of pressure is provided in the operating system and is connectable to the seal. Valve means connect the pressure source to the steam system if the sensing means detects a pressure below a set pressure sufficient to sustain a seal between the door and the surface.