单项选择题
A.Lube oil passing through the system
B.Moisture or foreign matter collecting at the valve seat and orifice
C.Variable spring tension caused by the changing temperature
D.Frost on the liquid line
单项选择题 Broken valve strips in an operating low pressure, air compressor will cause （）.
单项选择题 Which of the listed operating conditions would have the greatest effect on the volumetric efficiency of an operating reciprocating air compressor?（）
单项选择题 In order to distribute the side pressures over a wide area of the cylinder walls and liners, which of the listed types of pistons are used in modem low pressure air compressors?（）