单项选择题

If a centrifugal pump is driven by a constant speed electric motor and produces a discharge pressure less than designed, the cause is probably（）.

A.excessive pump speed
B.excessive suction head
C.worn wearing rings
D.gross pump misalignment

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单项选择题

Which of the following statements is correct relative to distillation plant operation?（）

A.Distillation is the process of boiling seawater to produce vapor which is condensed into fresh water
B.Evaporation is the second part of the distillation process where brine is removed
C.Brine is the result of condensed sea water vapor
D.Distillate is the product resulting from the evaporation of fresh water vapor

单项选择题

The amount of moisture in a given sample of air, when compared with the amount of moisture the air could hold if totally saturated at the existing temperature of the sample, is called （）.

A.absolute humidity
B.specific humidity
C.effective humidity
D.relative humidity

单项选择题

The purpose of an air compressor unloading device is to （）

A.drain water from the air receiver
B.drain water from the cylinders
C.delay the compression process until the motor is up to speed
D.check pump alignment