Abstract: An apparatus and a method for hermetically sealing a vacuum process chamber substantially without frictional force are provided. In the apparatus, a ball bearing is used between a door and a loader stage for facilitating the mounting of the former to the latter. A photosensing element is used which consists of a traversing flag mounted on a loader stage onto which a door is mounted, and a stationary photo transmitter/receiver mounted on the structure onto which a furnace tube is installed. The photosensing device enables the determination of the state of engagement between the door on the cantilever loader assembly and the flange on the furnace tube without any mechanical contact or frictional force occurring in the sensing device. A poorly mated interface between the door and the flange can thus be avoided and a substantially more reliable seal can be achieved between the sealing members.