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.
单项选择题 Air chambers are usually fitted to reciprocating pumps in order to （）.
单项选择题 Some pumps use packing as sealing glandThe gland should be （）.
