单项选择题
A.Radiation B.Conduction C.Natural convection D.All of the above
Which of the valves listed should be used either in the...
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
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
