单项选择题
A.frosting of the liquid line
B.higher than normal head pressure
C.a clear sight glass
D.abnormally cold reefer boxes
单项选择题 When installing a hydraulic hose, which of the following precautions should be taken?（）
单项选择题 A lube oil filter can be used to remove most contaminants from lube oilA contaminant which will remain in the lube oil after filtering is （）.
单项选择题 Which pump installation would require an external source of sealing water?（）