Isolation valve for single crystal pulling apparatus

Abstract

An isolation valve for a single crystal pulling apparatus providing a good sealing performance is disclosed. The apparatus comprises a casing having two opposite valve seats, a first valve seat having a first opening communicable with the main chamber of the apparatus, a second valve seat having a second opening communicable with the pull chamber of the apparatus. The body of the isolation valve includes a first plate movable in and out of contact with the first valve seat to open and shut the first opening, a second plate movable in and out of contact with the second valve seat to open and shut the second opening, and a bellows connecting the first and second plates. The isolation valve also comprises a holder holding the first plate out of contact with the first valve seat when the first plate is opposite to the first valve seat, a passage communicable with a fluid supply and the interior of the valve body, and a controller controlling the pressure of a working fluid supplied from the fluid supply into the interior of the valve body. The controller has a first set pressure at which the first and second plates are in contact with the first and second valve seats and a second set pressure at which the first and second plates are out of contact with the first and second valve seats.