| 摘要 |
PURPOSE:To make it possible to eliminate the necessity of an oil seal, by providing a pressure reducing chamber communicated with the suction side of a second stage side pump, in a rotary shaft coupling a first stage side rotor with a second stage side rotor. CONSTITUTION:A pressure reducing chamber 20 communicated with a passage 8 is formed in the intermediate section of a rotary shaft 4 coupling between first and second rotors 2, 3. Leakage gas from a chamber F causes the pressure in the shaft section of a second stage side pump to rise, and therefore, is liable to flow into the first stage side shaft section due to the pressure differential therebetween. However, the leakage gas reaches on its way the pressure reducing chamber 20 which is communicated with an suction side chamber D in the second stage side pump from which the leakage as is sucked and returned by the second stage side pump. Thus, it is possible to eliminate an oil seal used as a shaft seal between the first and second stage side pumps.
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