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
单项选择题 If a refrigeration compressor is running continuously without lowering the temperature in the refrigerated space, the trouble may be （）.
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 （）.
单项选择题 Which of the conditions listed represents the greatest effect of excess frost accumulation on the evaporator coils?（）