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單項(xiàng)選擇題

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

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單項(xiàng)選擇題

The gear, screw, and vane pumps are all classified as （）.

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

單項(xiàng)選擇題

The （） discharge a nearly constant amount of liquid regardless of pressure.

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