单项选择题

The pressure head of a water pump is given in the unit of （）.

A.kg
B.MPa
C.mH20
D.None of the above

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单项选择题

Which of the following are components of a mechanical seal? （）
(1) stationary ring
(2) rotational ring
(3) packing
(4)spring

A.(1), (2) and (3)
B.(1), (2) and (4)
C.(2), (3) and (4)
D.None of the above

单项选择题

A.variable stroke pumps
B.multistage pumps
C.positive displacement pumps
D.triple-ported pumps

单项选择题

A.mixed-flow pump
B.axial-flow pump
C.centrifugal pump
D.displacement pump