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单选题
Centrifugal pumps, however, can be designed with a number of impellers （） to attain a large amount of liquid.
A
in series
B
in parallel
C
assembled
D
together
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interconnectedC
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packed stuffing boxesC
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Decreasing the speed of rotation will decrease the discharge pressureC
Opening the discharge valve wider will increase the discharge pressureD
All of the above
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the number of fuel valvesB
the number of cylindersC
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They should always be started with the discharge valve closedB
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考题
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单选题Which of the following pumps belongs to centrifugal pump?（）A
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单选题Which of the materials listed is used as the dynamic seal material on mechanical seals installed on most centrifugal pumps used in water service?（）A
CopperB
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单选题Centrifugal pumps can be designed with a number of impellers （） to attain a high final delivery pressure.A
in seriesB
in parallelC
either A or BD
None of the above is tree
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单选题Centrifugal pumps are popular because they are very simple in construction,and produce smooth, constant, （） discharge.A
non-pulsatingB
pulsatingC
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单选题A centrifugal pump can’t supply water after startingYou should check （）.A
priming waterB
power supplyC
packing glandD
bearing lubrication
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