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单选题
Before liquid can flow into a pump, the air in the suction line must be （） sufficiently to cause the liquid to flow into the suction chamber.
A
filled
B
evacuated
C
compressed
D
charged
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centerline of the pump and the level of the liquid in the suction well when the source of liquid is below the pumpB
centerline of the pump and the suction liquid level when the source of liquid is above the pumpC
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lantern tings between the packing ringsC
a liquid sealD
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All of the above are true
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单选题Which of the listed conditions can lead to cavitation气穴in a centrifugal pump?（）A
Vapor pockets formed in the suction flow streamB
Rough easing volute surfacesC
Worn wearing ringsD
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