Which of the following pumps are self-priming, and can deal with liquid from a level below the pump: （）
(1)reciprocating
(2)vane
(3)gear
A.（1）only
B.（1）and（2）
C.（2）and（3）
D.（1），（2）and（3）
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Which of the following will be the advantage of a centrifugal pump as compared with a reciprocating pump?（）
(1) Its discharge is continuous
(2) It has no internal valves
(3) Upon accidental closing of discharge valve, excessive pressure will not build up
A.（1），（2）
B.（2），（3）
C.（1），（2），（3）
D.（2）only
A.reduce
B.rise
C.raise
D.fall
A.increase discharge pressure
B.increase suction vacuum
C.develop pulsation flow
D.keep a steady rate of flow
A.slack enough to allow slight leakage of fluid
B.slightly clocked
C.brought up tight so as not to allow any leakage
D.fitted with a relief valve
A.Volute pump
B.Diffuser pump
C.Regenerative pump
D.All of the above
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