单项选择题
Which of the valves listed should be used either in the fully opened or the fully closed position?（）
A.A gate valve
B.A globe valve
C.Any check valve
D.Any needle valve
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相关考题
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If a refrigeration compressor is running continuously without lowering the temperature in the refrigerated space, the trouble may be （）.
A.a shortage of compressor oil
B.warm food in the refrigerator
C.excessive condenser cooling water
D.a shortage of refrigerant -
单项选择题
In the design of hydraulic piping and equipment consideration is given to minimize turbulence in the hydraulic fluid, as this will cause （）.
A.molecular fluid vibration
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单项选择题
Which of the conditions listed represents the greatest effect of excess frost accumulation on the evaporator coils?（）
A.Keeps the refrigerated space cooler
B.Reduces the efficiency of the plant
C.Takes the load off the compressor
D.Has no affect on the system
