MAIN VALVE

PURPOSE:To stop a valve body steplessly in an optional position by providing the valve body larger than an exhaust port for opening and closing an opening part, connecting mutually opposed electric cylinders to the valve body, respectively, and providing a driving source for driving the electromagnetic cylinders, respectively. CONSTITUTION:Tow electric cylinders 10a, 10b are set around the exhaust port 5 of a vacuum chamber 4 opposite to each other, the vertically moving rods 17 of the electric cylinders 10a, 10b are protruded into the vacuum chamber 4. A disc valve body 2 larger than the exhaust port 5 to open and close the opening part through a plate 24 is fixed to the top ends of the rods 17. The electric cylinders 10a, 10b are connected to the valve body 2, the lower ends of ball screws 12 protruded from the bottom surfaces of the electric cylinders 10a, 10b are connected to each other through the shaft 34 and coupling 35 of a stepping motor 11, and the rotating motion of the stepping motor 11 is converted into a linear movement by the ball screws 12 so that the valve body 2 can be vertically moved and stopped steplessly at an optional position.