单项选择题 Centrifugal pumps can be designed with a number of impellers （） to attain a high final delivery pressure.

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

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