| 摘要 |
PROBLEM TO BE SOLVED: To suppress the backflow of a gas from a discharge port in high vacuum state to reduce the discharge power in an evacuation by use of a displacement vacuum pump for compressing the gas sucked through an inlet port and discharging it through the discharge port by throttling the opening area of the discharge port according to the reduction in pressure of the sucked gas. SOLUTION: When a male rotor 2 and a female rotor 3 are rotated within the rotor chamber 1a of a housing 1, a transfer chamber formed between the both is extended and contracted, so that a gas is sucked, compressed and discharged. When an evacuation is started, the slider 20a of a throttle valve 20 is pulled to the left by the effect of air pressure on the feed port 21c of an air cylinder 21 to keep the opening area of an internal discharge port 12a at the maximum. When the evacuation is progressed, and the sucking pressure is reduced to high vacuum, the slider 20a is pushed to the right by the effect of air pressure on another feed port 21b to throttle the opening area of the internal discharge port 12a to the minimum. According to this, the backflow of the gas in high vacuum can be suppressed to reduce the discharge power.
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