The main forms of valve damage are wear, bending and skew. The reasons are as follows:

　　①气门和气门座圈受高温、高压气体的冲击和承受工作过程中的机械负荷，容易烧蚀和磨损。气门与气门座圈的工作斜面，由于气门不停地开启和关闭，相互撞击、敲打，承受反复的冲击负荷，引起工作斜面的磨损、起槽、斑点和凹陷。

　　Valves and seat rings are easily ablated and worn by the impact of high temperature and high pressure gas and the mechanical load in the working process. The working incline of the valve and the valve seat ring is attacked, grooved, spotted and sunken due to the constant opening and closing of the valve, the impact and knocking of each other, and the repeated impact load.

　　②气门杆部在气门导管内运动时不断摩擦，润滑条件又差，加上窜进的灰尘磨料，使两者均受到磨损。

　　(2) When the valve rod moves in the valve conduit, it rubs continuously, and the lubrication condition is poor, together with the dust abrasive, which makes both of them suffer from wear and tear.

　　③气门导管内进人积炭结胶，加速气门杆与导管间的磨损。

　　(3) Carbon deposit cementing is introduced into the valve duct to accelerate wear and tear between the valve stem and the duct.

　　④气门杆尾端与摇臂之间相互撞击，使两者都受到磨损。

　　(4) The tail end of valve rod and rocker arm collide with each other, which makes both of them suffer from wear and tear.

　　⑤气门顶部受气缸内气体压力、气门杆尾端受凸轮通过挺柱的撞击，造成气门杆的弯曲。

　　The top of the valve is subjected to the gas pressure in the cylinder and the end of the valve rod is impacted by the cam passing through the tappet, which causes the bending of the valve rod.

　　⑥气门顶与活塞碰撞而使气门杆弯曲。

　　_The valve rod is bent by the collision between the valve top and the piston.

　　⑦气门杆尾端面摇臂间的间隙过小，受热膨胀后，顶住气门杆尾端而使其弯曲和端面不平。

　　_The clearance between rocker arms at the end of the valve rod is too small. After being heated and expanded, the end of the valve rod is held against and the bending and end surface of the valve rod are uneven.

　　⑧气门或气门座圈工作面与气门杆不同心，气门座与气门导管不同心而使气门杆弯曲。

　　_The working face of valve or valve seat ring is not concentric with the valve stem, and the valve seat is not concentric with the valve duct, which makes the valve stem bend.

　　⑨气门杆与气门导管受磨损后，使配合间隙增大，气门杆在管内晃动使气门歪斜，引起气门头部的偏磨。

　　_After wear and tear of the valve rod and the valve duct, the fit clearance increases, and the valve rod sloshing in the tube causes the valve to skew, causing eccentric wear of the valve head.

　　⑩气门杆弯曲后，形成气门顶部的歪斜和偏置。

　　_After the valve stem is bent, the inclination and offset of the top of the valve are formed.