A.the suction and discharge valvesB.tools and equipment……

单项选择题Which of the listed devices would be installed at a control system air pressure reducing station?（）

A.Moisture separator
B.Vacuum breaker
C.Lubricator
D.Non-return valve

单项选择题Power is defined as the （）.

A.rate of doing work
B.amount of force needed to overcome friction
C.amount of work accomplished
D.distance through which an object is moved

单项选择题To correct the condition of slugging and flooding back in a refrigeration system, it may be necessary to （）.

A.re-adjust the discharge pressure
B.clean the expansion valve screen
C.add refrigerant
D.adjust the expansion valve

单项选择题On small, low pressure, air compressors, the cylinders are usually lubricated by the （）.

A.splash method
B.mechanical force feed lubricators
C.detached sump method
D.internal cooling passages in the crankshafts and connecting rods

单项选择题While troubleshooting a refrigeration system for low head pressure, liquid refrigerant flooding back from the evaporator is determined to be the causeIt may be necessary to （）.

A.change the expansion valve adjustment
B.readjust the water regulating valve to increase the flow of water
C.purge air from the condenser
D.clean the waterside of the condenser