单项选择题
A.maintain adequate coil back pressure
B.prohibit flashing in the liquid line
C.reduce refrigerant volume in the system
D.reduce compressor discharge line loading
单项选择题 An advantage of a helical gear pump over a simple gear pump is that the helical gear pump is capable of （）.
单项选择题 The size of ball and roller bearings can be identified by the （）.
单项选择题 A centrifugal pump produces flow with a resulting discharge head by energy conversionIt is typical for the energy conversion to follow the order of （）.