| 摘要 |
PURPOSE:To simplify assembling and to remove pipe connecting part so as to remove gas leakage by forming a communication passage to a suction port and a return passage leading to a pump chamber inside a casing so as to miniaturize and make compact outside dimension. CONSTITUTION:Communication passages 38, 41 are provided inside a casing 25 between the first pump chamber 12 and the second pump chamber 13 and communicate with suction ports 27, 32. Further return passages 51, 52, 53 which communicate with the first, the second and the third pump chambers 12, 13, 15 are provided beside discharge ports 22, 28, 33 positioned inside the casing 25. Since the communication passages 33, 41 and return passages 51, 52 are thus formed inside the casing 25, outside dimension can be made small and compact, trouble in assembling is small and there is no pipe connecting part, so gas leakage from these pipe connecting part can be get rid of.
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