單項(xiàng)選擇題An advantage of a helical gear pump over a simple gear pump is that the helical gear pump is capable of （）.

A.maintaining a steadier speed
B.delivering liquids over greater distances
C.operating for longer periods of time
D.producing a smoother discharge flow


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1.單項(xiàng)選擇題The size of ball and roller bearings can be identified by the （）.

A.rolling member size
B.inner race cone width
C.manufacturers numerical code
D.outer ring width

2.單項(xiàng)選擇題A centrifugal pump produces flow with a resulting discharge head by energy conversionIt is typical for the energy conversion to follow the order of （）.

A.mechanical energy to kinetic energy to potential energy
B.mechanical energy to potential energy to kinetic energy
C.potential energy to mechanical energy to kinetic energy
D.kinetic energy to mechanical energy to potential energy

3.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

4.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

5.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