单项选择题
In a fixed displacement axial piston hydraulic motor, the speed is varied by（）
A.regulating the ratio between torque and speed via the torque limiter at the motor B.directing the motor output flow through a bypass line C.maintaining a constant flow and pressure input D.controlling the input flow rate
单项选择题 In a shell-and-tube type hydraulic fluid cooler, the amount of heat transferred from the hydraulic fluid to the cooling water depends upon（）
单项选择题 An orifice-check valve placed in a hydraulic system is used to（）
单项选择题 Purging air from a hydraulic system is necessary when（）
