单项选择题
Purging air from a hydraulic system is necessary when（）
A.adding small amounts of oil to the system B.the system has been overheated C.the system has been drained and then filled with new oil D.the system has been idle for a long period of time
单项选择题 Leakage of hydraulic fluid from around the shaft of a hydraulic motor may be caused by（）
单项选择题 Air trapped in the hydraulic fluid of a steering system would be indicated by（）
单项选择题 How can the chance of contaminating hydraulic fluid be decreased when working on hydraulic system?（）
