单项选择题

A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.

A.backwards
B.forwards
C.upward
D.downwards

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单项选择题

When installed for bilge pumping or ballast duty, centrifugal pumps require a （） to remove air from the suction pipe.

A.air chamber
B.head lank
C.primer
D.prime mover

单项选择题

Water enters the rotating impeller through the entry, known as “（）”, at the centre.

A.eye
B.hole
C.balance holes
D.opening

单项选择题

Which one is not the normal operation for boiler shutdown?（）

A.Carry out soot blowing if permissible
B.Change fuel supply to diesel oil
C.Close steam stop valves on boiler when pressure is reduced
D.Drain boiler empty when it has cooled down