Abstract: A sealing arrangement for a vacuum processing system for semiconductor wafers which is effective to apply a sealing force to a valve element (66) between chambers of the processing system. The valve element is defined by a platen which holds wafers (30) for transfer between a horizontal receiving position within a staging chamber (14) to a vertical position within a processing chamber (16-19). The sealing arrangement includes a pair of toggle mechanisms (268) which are manually operable from outside the staging chamber and which, in conjunction with the closing force applied by the platen operating mechanism (165) are effective to maintain vacuum integrity within the staging chamber when the process chamber is at atmospheric pressure or removed for servicing.