单项选择题
A.valve loop
B.valve uniflow
C.valve overlap
D.valve grinding
单项选择题 The period of valve overlap is when （）.
单项选择题 The outside diameter of the pipe is （） the diameter of the bore of the piston rod, the result being that an annular space formed between the piston rod and the pipe.
单项选择题 The outside diameter of the pipe is （） the diameter of the bore of the piston rod, the result being that an annular space formed between the piston rod and the pipe.