Embodiments disclosed herein generally relate to methods for sealing a processing chamber with a slit valve door. The door initially raises from a position below the opening for the processing chamber to a raised position. The door then expands until an O-ring that is on the door just touches the sealing surface. Then, the door expands again to compress the O-ring against the sealing surface. The door expands by flowing a gas into the interior volume of the door. By controlling the pressure buildup within the door, the speed with which the door expands is controlled to ensure that the door gently contacts the sealing surface and then compresses against the sealing surface. Thus, the door may be prevented from contacting the sealing surface with too great a force that may jolt or shake the processing chamber and produce undesired particles that may contaminate the process.