单项选择题
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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单项选择题
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 -
单项选择题
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 -
单项选择题
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
