The role of the valve is specifically responsible for the input of air into the engine and exhaust after combustion. From the engine structure, it is divided into intake valve and exhaust valve. The function of the intake valve is to suck air into the engine and mix and burn with fuel; the function of the exhaust valve is to discharge the burned exhaust gas and dissipate heat.
The valve is composed of a valve head and a stem. The temperature of the valve head is very high (intake valve is 570~670K, exhaust valve is 1050~1200K), and it also bears the pressure of gas, the force of the valve spring and the inertia force of the transmission component. Its lubrication and cooling conditions are poor, and the valve must be required It has certain strength, rigidity, heat resistance and wear resistance. The intake valve is generally made of alloy steel (chromium steel, nickel-chromium steel), and the exhaust valve is made of heat-resistant alloy (silicon-chromium steel). Sometimes in order to save heat-resistant alloys, heat-resistant alloys are used for the head of the exhaust valve and chrome steel is used for the stem, and then the two are welded together.
The material of the valve is usually divided into 40Cr, 4Cr9Si2, 4Cr10Si2Mo, 21-4N and 23-8N in China. 5Cr8Si2, 4Cr9Si3, 21-2N, 21-12N, 23-8N, XB, etc. have been used in large quantities on some imported models. High-temperature nickel-based alloys have also begun to be applied to exhaust valves of high-load diesel engines.