單項(xiàng)選擇題If an operating bilge pump is developing good vacuum, but is unable to discharge any water, which of the following problems is the most probable cause?（）

A.The wearing rings are excessively worn
B.The suction strainer is clogged
C.The discharge valve is clogged
D.The shaft is worn


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1.單項(xiàng)選擇題The sudden reduction of pressure occurring within the crankcase of a refrigeration compressor during starting causes the （）.

A.sudden evaporation of wax crystals in the lubricant
B.sudden evaporation of entrapped air in the lubricant
C.release of refrigerant from the oil/refrigerant mixture
D.release of dissolved lubricant from the refrigerant

2.單項(xiàng)選擇題One of the consequences in continuing to operate a centrifugal bilge pump with the discharge valve closed, is that the （）.

A.motor overload will open
B.relief valve will open
C.pump will overheat
D.motor will overheat

3.單項(xiàng)選擇題Which of the following statements is correct concerning a typical shipboard multi-coil refrigeration system?（）

A.The liquid receiver functions to collect and remove non-condensable gases
B.A thermostatic expansion valve is used to control refrigerated space temperature
C.Refrigerant temperature in an evaporator is directly related to refrigerant pressure
D.Dehydrators must be used continuously in a refrigeration system

4.單項(xiàng)選擇題The basic function of the centrifugal pump impeller is to （）.

A.directly increase the pressure of the liquid being pumped
B.directly increase the velocity of the liquid being pumped
C.convert the potential energy of the liquid to kinetic energy
D.separate air from the liquid being pumped

5.單項(xiàng)選擇題Excessive oil foaming in the crankcase of a refrigeration compressor can result in （）.

A.overheated compressor bearings
B.excess lube oil viscosity
C.carbon deposits on the compressor piston rings
D.wax crystals forming in the lubricant