单项选择题
Which of the listed statements is correct concerning the starting of centrifugal pumps?（）
A.They should always be started with the discharge valve closed
B.They should always be started with the discharge valve opened
C.A priming pump is always required to flood the impeller suction
D.They should always be started with the sealing line valves closed
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相关考题
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单项选择题
Excessive oil foaming in the crankcase of a refrigeration compressor at start up can cause（）.
A.compressor damage from improper lubrication
B.refrigerant absorption by the lubricant
C.increased viscosity in the lubricant
D.carbon deposit on the compressor suction valves -
单项选择题
Which of the valves listed is NOT considered to be a hydraulic system directional control valve?（）
A.Spring-centered valve
B.Unloading valve
C.Three-position valve
D.Two-position valve -
单项选择题
Which of the listed refrigeration system components keeps the refrigerant circulating through the system?（）
A.Expansion valve
B.Condenser
C.Evaporator
D.Compressor
