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单选题
The amount of fluid delivered by a helical pump can be regulated by （）.
A
throttling the pressure line
B
changing the speed of the rotor
C
either A or B
D
None of the above is tree
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A substance must be cold in order for it to be pumpedC
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A pump must receive its energy from an external source
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excessive internal leakage in the pumpB
low discharge pressure and fluid flowC
excessive fluid level in the hydraulic reservoirD
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单选题An advantage of a helical gear pump over a simple gear pump is that the helical gear pump is capable of （）.A
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delivering liquids over greater distancesC
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单选题A pump is defined as device that（）A
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考题
单选题The amount of fluid delivered by a positive displacement pump can be regulated by （）.A
throttling the pressure lineB
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None of the above is tree
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单选题Which of the listed conditions can lead to cavitation气穴in a centrifugal pump?（）A
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Rough easing volute surfacesC
Worn wearing ringsD
Heavy fluid in the flow stream
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varying the pump discharge pressureB
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单选题The pressure head of a pump is given in the unit of （）.A
kgB
MPaC
meter fluid columnD
None of the above is true
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