单项选择题
A.only by the pump as its primary function
B.by resistance to the fluid flow through the system
C.by the thermal input to the systems fluid
D.solely by the charge applied by the accumulators
单项选择题 If a large difference exists between the compressor discharge pressure and the pressure corresponding to the existing condensing temperature in a refrigeration system, you should（）.
单项选择题 Which of the following statements concerning butterfly valves is correct?（）
单项选择题 The simplest method to use for determining if a centrifugal pump is operating as designed, is to （）.