| 摘要 |
PURPOSE:To prevent the lowering of an ultimate vacuum due to the leakage of a lubricant to a suction side by providing a shaft sealing means which is held below the atmospheric pressure and a shaft sealing means which is held at the atmospheric pressure in this order from a rotor chamber side, in between the suction side bearing and said rotor chamber of a screw type vacuum pump. CONSTITUTION:A first shaft sealing means 13 and a second shaft sealing means 14 are provided in this order from a rotor chamber 7 side in between the suction side bearing 12 and the rotor 7 of a screw type vacuum pump body 1. The first shaft sealing means 13 is connected to a space in a condition immediately after a low pressure is confined in it, through a through holes 18, 19 and a connecting pipe 20 to keep the means 13 under the atmospheric pressure, while the second shaft sealing means 14 is connected to the atmosphere through a through hole 17. Thereby, pressure difference between the first shaft sealing means 13 and a suction port is small, preventing the inside of the rotor chamber 7 from being polluted by the lubricant, needless to say preventing the air or the lubricant from leaking out to a suction port lowering an ultimate vacuum.
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