单项选择题
A centrifugal pump may fail to deliver water when first started if the （）.
A.water seal pipe is plugged B.pump is not primed C.seal ring is improperly located D.impeller is flooded
单项选择题 Which features of a centrifugal pump reduce the need for renewing worn impellers and pump casings?（）
单项选择题 When securing a flash-type evaporator for an extended period of time, you should （）.
单项选择题 A distinguishing feature of an educator, when compared to other pumps, is the （）.
