单项选择题The ratio of the weight of moisture contained in a given volume of air, to the weight of moisture that the same sample would hold if saturated, is called the().

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


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1.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

2.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

4.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

5.单项选择题Personnel working with refrigeration systems, and subject to the exposure of refrigerants should wear ().

A.face shield
B.a respirator
C.rubber gloves
D.an all purpose gas mask

7.单项选择题If the capacity of a centrifugal pump decreases gradually over a long period of time, you should replace the ().

A.packing gland
B.mechanical seals
C.lantern rings
D.wearing rings

8.单项选择题Distilled water from an evaporator may be discharged into a potable water tank ().

A.through a detachable hose connection
B.after passing through an activated charcoal filter
C.after chemical analysis shows it is fit for consumption
D.through a solenoid operated three-way valve

9.单项选择题If a centrifugal pump vibrates and is noisy when operating, the cause could be ().

A.worn gland sealing shaft
B.worn wearing rings
C.a bent shaft
D.reversed pump coupling

10.单项选择题Which of the devices listed is common to all types of pumps?()

A.A power end and fluid end
B.A propeller and educator
C.A volute and impeller
D.A turbine and piston