单项选择题
The function of a centrifugal pump double volute casing is to （）.
A.reduce radial thrust to the impeller
B.double the liquid velocity through the pump when compared to a single volute
C.reduce hydraulic end thrust
D.provide the effect of multi-staging
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单项选择题
Dirt should not be allowed to contaminate a grease lubricant because the （）.
A.dirt will cause corrosion of bearing
B.bearings will leak oil excessively
C.dirt is very abrasive when mixed with grease
D.grease will become inflammable -
单项选择题
The presence of bubbles in a refrigeration system liquid line may （）.
A.promote refrigerant dehydration
B.be absorbed in the receiver
C.cause low condensing pressure
D.carry moisture and lead to corrosion -
单项选择题
Air entering an air-cooled refrigeration system is indicated by （）.
A.frosting of the liquid line
B.higher than normal head pressure
C.a clear sight glass
D.abnormally cold reefer boxes
