| 摘要 |
PURPOSE:To make it possible to hold a vacuum chamber to a reduced pressure state in a predetermined range, by attaching a three-way solenoid valve between the vacuum chamber and a vacuum pump, and switching over the three-way solenoid valve by a pressure sensor. CONSTITUTION:When the pressure of a vacuum chamber 2 is lowered to predetermined one by a vacuum pump 2, a control circuit 3 is operated by the signal of a pressure sensor 5 and the supply of a current to a three-way solenoid valve 11 is cut off to close a valve 11a and the reduced pressure state in the vacuum chamber 2 is held while the suction side of the vacuum chamber 2 is opened to the open air and the supply of a current to the pump 12 is cut off. When the pressure in the vacuum chamber 2 rises, the control circuit 3 is operated by the signal of the pressure sensor 5 and the vacuum pump 12 is operated while the valves 11a, 11b of the three-way solenoid valve 11 are communicated and the vacuum chamber 2 is evacuated instantaneously. |
