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單項選擇題

A reciprocating pump belongs to （） according to its working principle.

A.injector pumps
B.positive displacement pumps
C.centrifugal pump
D.centripetal pumps

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單項選擇題

Shaft sealing in a centrifugal pump can be effected by （）.

A.the mechanical seal
B.packed stuffing boxes
C.either A or B
D.neither A nor B

單項選擇題

As for a hydraulic vane pump, which of the following is in contact with the vanes during working: （）
(1)the rotor
(2)the pump shaft
(3)the external surface of the housing

A.(1) only
B.(2) only
C.(1) and (2)
D.(1),(2)and(3)