单项选择题
A.Variable volumes can be obtained with gear pumps only by variation of the pump drive speed
B.A radial piston pump houses sliding pistons in a stationary cylinder block through which passes a rotating pintle or ported shaft
C.The amount of fluid displaced per revolution of an axial piston rotary pump is dependent on the angle formed between the cylinder block and valve plate
D.All of the above
单项选择题 The function of the hydraulic telemotor transmitter used in an electro-hydraulic steering gear system is to （）.
单项选择题 To obtain maximum efficiency, two stage air compressors are usually （）.
单项选择题 Which of the following statements is true concerning the overall efficiency of air compressors?（）