Vacuum regulating valve

A vacuum regulating valve comprising:

• a valve unit including a valve casing having an axis, provided with a first main port to be connected to a vacuum vessel, a second main port to be connected to a vacuum pump, an internal passage connecting the first and the second main port, a valve seat surrounding the first main port, a valve element placed in the valve casing and capable of being seated on the valve seat, a valve stem extending from the valve element backward along the axis of the valve casing, a partition wall attached to the back end of the valve casing, a return spring extended between the partition wall and the valve element to urging the valve element toward the valve seat so that the valve element may be seated on the valve seat;
• a cylinder actuator including a cylinder joined to a back end of the valve casing and provided with a pilot port, a piston axially slidably fitted in the cylinder so as to define a pressure chamber connected with the pilot port through which a pilot fluid is supplied into the pressure chamber, and connected to a back end of the valve stem;
• and
• a valve opening regulating unit for regulating operating position of the piston to regulate valve opening, including a valve opening setting shaft having one end in contact with a back surface of the piston, and a driving mechanism capable of continuously axially moving the valve opening setting shaft in either of opposite directions to a desired position to set the vacuum regulating valve for a desired valve opening by setting the piston at an operating position,
• wherein the driving mechanism includes an electric motor having an output shaft capable of being rotated in opposite directions, and a motion converting mechanism capable of converting rotational motions of the output shaft of the electric motor into linear motions in opposite directions, and the valve opening setting shaft is connected to the motion converting mechanism, and
• the motion converting mechanism includes a rotating screw rod connected to the output shaft of the electric motor, and an internally threaded nut mounted on the screw rod, restrained from turning and capable of moving axially along the screw rod, and the valve opening setting shaft has a base end connected to the nut, and a free end that can come into contact with and can separate from the piston.