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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热门试题

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

单项选择题Which of the listed components is considered to separate the high pressure side of a refrigeration cycle from the low pressure side of the cycle?（）

A.The condenser and the expansion valve
B.The king valve and the solenoid valve
C.The compressor and the expansion valve
D.The condenser and the solenoid valve

单项选择题A compound gage is used to measure （）.

A.temperature and pressure
B.humidity and temperature
C.pressure and vacuum
D.pressure and humidity