单项选择题
A.the slewing motor B.the luffing motor C.the hoisting motor D.none of the above
External and internal leakage in hydraulic systems may ...
单项选择题External and internal leakage in hydraulic systems may be caused by （）.
A.unusual vibration B.excessive worn parts C.abnormal pressure D.any of the above
What type of valve is used to direct the flow of hydrau...
单项选择题What type of valve is used to direct the flow of hydraulic fluid?（）
A.Relief valve B.Direction control valve C.Stop valve D.Pressure control valve
The rotor of the hydraulic motor rotates at a speed pro...
单项选择题The rotor of the hydraulic motor rotates at a speed proportional to the （）.
A.flow of oil B.pressure of oil C.A and B D.temperature of oil
