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)vane
(3)gear
A.（1）only
B.（1）and（2）
C.（2）and（3）
D.（1），（2）and（3）
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单项选择题
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 -
单项选择题
The pipe friction and the resistance will （） as a result of an increase in the amount of fluid flowing through the system.
A.reduce
B.rise
C.raise
D.fall -
单项选择题
Air chambers are usually fitted to reciprocating pumps in order to （）.
A.increase discharge pressure
B.increase suction vacuum
C.develop pulsation flow
D.keep a steady rate of flow
