单项选择题

A refrigeration system compressor crankcase is sweating or unusually coldThis is an indication of（）.

A.a shortage of refrigerant in the system
B.air in the system
C.an accumulation of liquid refrigerant in the crankcase
D.a shortage of oil in the crankcase

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When the desired rudder angle is attained by a typical double mm electro-hydraulic steering gear,the（）.

A.ram relief valves bypass oil to stop rudder movement
B.six-way valve shifts to the neutral flow position
C.steering pump electric motor is de - energized by the transfer switch
D.follow-up gear takes the hydraulic pump off stroke

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A swing check valve is used in a pipeline to （）.

A.maintain a preset pressure on the line
B.closely regulate the amount of flow
C.relieve excessive pressure on the line
D.allow flow in one direction only

单项选择题

Sluggish response or action of the hydraulic actuators may be a result of （）.

A.insufficient load
B.excessively high oil viscosity
C.relief-valve pressure setting too high
D.reservoir level being maintained two inches above normal