单项选择题
A.bypass the high pressure stage to the low pressure stage on 100% of the air compressors in service
B.prevent excessive inter-stage pressure buildup
C.control compressor discharge pressure
D.remove all but the frictional load during starting
单项选择题 After installing a new hydraulic pump in a system, what special attention should be given to the hydraulic system?（）
单项选择题 For safe storage, the maximum allowable temperature to which refrigerant bottles should be exposed is （）.
单项选择题 One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.