| 摘要 |
The invention reduces power consumption and makes rotor with ease. As illustrated in FIG. 2, a multistage roots pump ( 1 ) in the invention including upstream rotors (R 1 a, R 1 b, R 2 a, R 2 b) having multiple teeth, supported by a pair of revolving shafts (A 1 , A 2 ); and downstream rotors (R 3 a, R 3 b~R 5 a, R 5 b) having identical number of teeth ( 31 ) with the upstream rotors, supported by revolving shafts (A 1 , A 2 ). The discharge area formed by the outer periphery of the downstream rotors (R 3 a, R 3 b~R 5 a, R 5 b) and the inner periphery of the pump chambers (P 1 ~P 5 ) is smaller than that of the upstream rotors (R 1 a, R 1 b, R 2 a, R 2 b).
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