The working conditions of exhaust valves in marine diesel engine accessories are very harsh. The bottom of the valve is in direct contact with high-temperature combustion products. During the opening of the valve, it also withstands high temperatures (900 ~ 1000 * C) and high speed with corrosive gases (up to 600m / s) Flushing, the central temperature of the gas valve is up to 700 ~ 800 ° C, and the temperature is also 600 ~ 700 ° C in the middle of the transition arc between the valve disc and the stem. The working temperature distribution of the exhaust valve.

      If the temperature is too high, the mechanical properties of the metal material will be reduced, and the material will be thermally deformed. When the valve face is not tightly sealed, it will cause high temperature gas to burn the valve face. When the valve is seated, under the combined action of the inertial force of the valve and the valve seat and the spring force, it also bears a considerable impact alternating load. This load will be obvious when the valve is beating or the valve gap increases. increase. The impact of the valve and the valve seat is likely to cause deformation of the sealing surface and severe wear. Most marine diesel engines are mostly supercharged diesel engines. Because the pressure of the fresh air in the intake port prevents the possibility of obtaining lubricating oil from the valve duct, dry friction is likely to occur between metals.

      However, there is always a layer of lubricating oil such as lubricating oil or smoke oil between the gas valve of the general diesel engine and the alloy surface of the exhaust valve seat of the supercharged diesel engine. In addition, wear will also occur between the valve stem and the catheter, and the tip of the valve stem is impacted and worn by the rocker arm. Therefore, these bad habits of operating and maintaining diesel engines are also the factors that cause the failure of diesel engine valves.