Embodiments of a valve assembly for a process chamber having improved seal performance are provided herein. In some embodiments, a valve assembly for a process chamber includes a housing having an opening disposed in a wall thereof and through which a substrate may be transferred; a door movably coupled to the housing in a plane substantially parallel to the wall of the housing for selectively sealing the opening; a compressible sealing member disposed at least partly between an upper surface of the door and a corresponding surface of the housing for forming a seal therebetween by compression of the compressible sealing member in a direction substantially perpendicular to the wall when the door is in a closed position; and a mechanism for restricting the exposure of the compressible sealing member to an environment on a process chamber side of the housing.