单项选择题
A.The high discharge pressure of the rotary pumps permits a larger volume of fluid per unit time than the reciprocating pump
B.Rotary pumps are capable of pumping more fluid than reciprocating pumps of the same weight
C.Rotary pumps occupy only one-half the space of reciprocating pumps
D.Rotary pumps eliminate discharge slippage of the pumped liquid, while this does not hold true for a reciprocating pump
单项选择题 If a reciprocating air compressor has a knock occurring in frequency with its operating RPM, the cause is probably （）.
单项选择题 Why are removable sleeves installed on centrifugal pump shafts?（）
单项选择题 In reference to air conditioning, when air attains the maximum amount of moisture it can hold at a specific temperature, it is said to be （）.