The valve is composed of a valve head and a valve stem. The temperature of the valve head is very high (570~670K for the inlet valve and 1050~1200K for the exhaust valve), and it also bears the pressure of the gas, the force of the valve spring and the inertia force of the transmission components. Its lubrication and cooling conditions are poor, so the valve must have certain strength, stiffness, heat resistance and wear resistance. The inlet 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 alloy, the exhaust valve head is made of heat resistant alloy and the rod is made of chrome steel, and then the two parts are welded together.

The shape of valve head includes flat top, spherical top and horn top. Generally, flat roof is used. Flat top valve head has simple structure, convenient manufacturing, small heat absorption area, small mass, and can be used for both intake and exhaust valves. Spherical top valve is suitable for exhaust valve. It has high strength, small exhaust resistance and good exhaust gas elimination effect, but it has large heating area, large mass and inertia, and complex processing. The horn type has a certain streamline, which can reduce the intake resistance, but its head has a large heating area and is only suitable for the intake valve.