单项选择题
Reduced capacity, accompanied by vibration and noise at the suction of a centrifugal pump is a result of （）.
A.cavitation B.water hammer C.fluid friction D.steam knock
单项选择题 The refrigerant leaves the evaporator of a refrigeration system as a low pressure （）.
单项选择题 When operating with a negative suction head, which of the following types of pumps will require priming?（）
单项选择题 The discharge rate or capacity of a centrifugal pump will vary directly as the （）.
