单项选择题

An excessive amount of water is prevented from entering a vessel using a water lubricated stern tube bearing by the use of the （）.

A.propeller hub
B.lignum vitae
C.shaft packing
D.labyrinth seal

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单项选择题

Under normal conditions, the refrigerant enters the compressor in an operating refrigeration system as a （）.

A.liquid
B.dry saturated gas
C.wet saturated gas
D.superheated vapor

单项选择题

Some vessels are equipped with a water lubricated stern robeWhen at sea, operating under normal conditions, the water service valve from the ships saltwater system to the bearing should be （）.

A.closed, and no leakage permitted across the shaft packing
B.closed, and only slight leakage permitted across the shaft packing
C.open, and no leakage permitted across the shaft packing
D.open, and only slight leakage permitted across the shaft packing

单项选择题

Sub-cooling is a method of reducing the temperature of the liquid refrigerant below its （）.

A.freezing point
B.floc point
C.condensing temperature
D.compression temperature