Small four-wheel tractor air brake valve tappet is made of plastic, its diameter and length are often susceptible to the impact of thermal expansion and contraction change, resulting in failure of the gas brake valve. 1, the size changes and failures When tappet diameter becomes larger fishing technology, it will produce a stuck brake valve housing failure so that the valve body can not open, no air, no deflation, or at Open position does not return to animal protection, not inflatable, no pressure; when the tappet length becomes shorter, the valve body parts open fishing, no air, no deflation. 2, the solution When the tappet diameter becomes larger, the length becomes longer, the fine sandpaper can be gently polished after the loading pull test until meet the requirements so far; when the tappet becomes shorter, tappet head and the valve body together Between the election pad thickness 1mm-2mm, outer diameter of φ18mm ordinary flat pads 1-2 can be. Of course, fundamentally solve the problem or to improve the quality of the tappet and the size of the village.