1. During the maintenance of mixer truck, if the valve is ablated, pitted and sunken, it shall be polished, which is generally carried out on the grinder. Four problems need to be paid attention to during operation:

一是保证气门头与杆部同心，否则应先校直；

First, ensure that the valve head is concentric with the rod, otherwise it shall be straightened first;

二是光磨辆在能磨出完整的锥面的前提下是越小越好；三是尽量提高表面光洁度；四是气门杆端部凹陷应予以磨平。

Second, on the premise that the smooth grinding vehicle can grind a complete cone, the smaller the better; Third, try to improve the surface finish; Fourth, the depression at the end of the valve stem shall be ground flat.

2、气门导管的铰销气门杆与气门导管配合间隙是决定气门导管使用寿命的关键，因此当更换新的气门导管时，铰销时应严格掌握好配合间隙，使用各搅拌车车型规定间隙的下限，可有效延长使用寿命。

2. The fit clearance between the hinge pin valve stem and the valve guide of the valve guide is the key to determine the service life of the valve guide. Therefore, when replacing the new valve guide, the fit clearance shall be strictly controlled when the hinge pin is used, and the lower limit of the clearance shall be specified for each mixer model, which can effectively prolong the service life.

3、气门的研磨气门的研磨分为两种情况：

3. Grinding of valve grinding of valve is divided into two cases:

一是气门与气门座只有轻微麻点，不需要光磨和铰销时的研磨；

First, there is only slight pitting between the valve and the valve seat, so there is no need for smooth grinding and grinding during hinge pin;

二是气门与气门座均经过光磨和铰销后的研磨。前者先用足金钢砂研磨，将麻点研磨掉后，再用细金刚砂研磨，涂上机油研磨，直密封符合要求，宽度符合规定为止。后者只有密封性达不到要求时才进行研磨，但操作时要注意，不要过分用力，严禁将气门上下敲打，否则将出现凹形砂痕，影响维修质量。

Second, the valve and valve seat are ground after smooth grinding and hinge pin. The former shall be grinded with full gold steel sand first, and then the pitting shall be grinded off, and then grinded with fine emery and coated with engine oil until the sealing meets the requirements and the width meets the regulations. The latter can only be grinded when the sealing performance fails to meet the requirements, but pay attention not to use excessive force during operation. It is strictly prohibited to knock the valve up and down, otherwise concave sand marks will appear, affecting the maintenance quality.