单项选择题

A positive displacement pump is that where the volume of the pump chamber is alternately increased to （） and then decreased to （）.

A.draw the liquid in；force the liquid out
B.force the liquid out；draw the liquid in
C.suction；draw
D.deliver；outlet

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单项选择题

A.throttling the pressure line
B.changing the speed of the rotor
C.either A or B
D.None of the above is tree

单项选择题

Which of the following pumps are self-priming, and can deal with liquid from a level below the pump? （）
(1) reciprocating
(2) rotary
(3) centrifugal

A.(1)only
B.(1)and (2)
C.(1),(2)and(3)
D.(2)and(3)

单项选择题

A.throttling the pressure line
B.changing the speed of the driving rotor
C.either A or B
D.None of the above is tree