单项选择题

Air line lubricators are used in compressed air systems to lubricate （）.

A.the suction and discharge valves
B.tools and equipment served by compressed air
C.air line reducing valves
D.all of the above

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单项选择题

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

单项选择题

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

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