单项选择题
A.A gate valve B.A globe valve C.Any check valve D.Any needle valve
If a refrigeration compressor is running continuously w...
单项选择题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
In the design of hydraulic piping and equipment conside...
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 B.energy losses C.wide pressure variations D.mechanical damage to control valves
Which of the conditions listed represents the greatest ...
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
