A patent document 1 (U.S. Pat. No. 6,390,448) discloses a Gate Valveswherein mutually opposing walls of the gate valve body are formed with a PC (process chamber) opening and a TC (transfer chamber) opening, respectively, and the PC opening and the TC opening are selectively closed with a double-sided valve member having a PC-side valve element and a TC-side valve element. With the disclosed technique, for example, the TC opening is closed to keep the transfer chamber at a vacuum while the process chamber is opened to the atmosphere, thereby making it possible to carry out repairs in the process chamber while using the transfer chamber at a vacuum. Moreover, it is possible to replace the seal of the PC-side valve element in a state where the TC-side opening is closed with the TC-side valve element. It is also possible to prevent fragments, contaminants, etc. in the process chamber from entering the transfer chamber. Thus, it is possible to continue an operation in one vacuum chamber during the repair of the other vacuum chamber or during the repair of the valve element in the other vacuum chamber.

The GATE VALVES in the patent document 1 tilts a single shaft at an upper position to allow the double-sided valve member to selectively close the PC opening and the TC opening and to place the double-sided valve member in an intermediate position between the two openings. When the single shaft is moved to a lower position, the two openings are fully open, thereby allowing a workpiece to pass therethrough. To perform these operations, the single shaft is secured to the double-sided valve member, and the single shaft is moved with three air cylinders. However, the use of three air cylinders causes an increase in size of the gate valve and also a rise in cost. Meanwhile, it is possible to clean the seal surfaces of the two walls of the valve body by removing the top cover from the valve body. However, it is impossible to replace the seals of the double-sided valve member. In addition, a space for cleaning is provided between each valve element and the associated wall, and the valve elements are coupled by using hinge pins. Thus, the spacing between the valve elements is large, and hence the longitudinal width of the valve body is unfavorably large.

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