单项选择题
A.noise and vibration B.an increase in discharge pressure C.an increase in suction pressure D.lifting of the relief valve
One cause of high head pressure occurring in a refriger...
单项选择题One cause of high head pressure occurring in a refrigeration system can be （）.
A.insufficient cooling water flow to the condenser B.a low refrigerant charge in the system C.the liquid valve is open too much D.high evaporator superheat
The control mode in which the final control element is ...
单项选择题The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
A.dead band action B.neutral zone action C.range D.on-off action
Pitting in the suction areas of a centrifugal pump bron...
单项选择题Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
A.cavitation B.electrolysis C.abrasion D.corrosion
