Engine valves are mechanical components used in internal combustion engines to control the flow of fluid and gas to or from the combustion chambers and cylinders during engine operation. They perform similarly to many other types of valves, blocking or allowing flow, but differ in that they are purely a mechanical device that works in conjunction with other engine components to open and close in the correct order with the correct timing. Engine valves are found in many types of combustion engines, whether they run off gasoline, diesel, kerosene, natural gas, or propane. In this blog, we will discuss the three main types of engine valves in detail.
While engine valves can be characterized by their function (intake/exhaust), they are most commonly distinguished by their design and materials. The three primary types of engine valves are monometallic engine valves, bimetallic engine valves, and hollow engine valves. Monometallic engine valves are the simplest type. As their name suggests, they are made from a single material that forms both the valve stem and valve head. They are popular for their high heat resistance as well as their anti-friction capabilities.
Bimetallic engine valves, sometimes called bimetal engine valves, are fabricated by welding together different materials to create a valve that has an austenitic steel valve head and martensitic steel valve stem. The properties of each steel make them ideal for their unique purpose. The austenitic steel on the valve head offers temperature and corrosion resistance, while the martensitic steel valve stem offers high tensile strength and resistance to abrasive wear.
Hollow engines valves are the most complex, featuring a special bimetallic valve that contains a hollow cavity filled with sodium. The sodium liquifies as the valve temperature rises and is circulated by the motion of the valve, helping to dissipate heat from the hotter valve head. The valve’s hollow design provides better heat transfer through the stem due to the martensitic stem material being a better conductor of heat than the austenitic steel of the head.
Hollow valves are ideal for modern engines that deliver more power from smaller, denser engines with higher exhaust gas temperatures that solid valves could not handle. The higher exhaust temperatures in modern engines result from three conditions: the desire for lean-burn combustion processes that reduce greenhouse gas emissions, engine designs with higher compression ratios and combustion pressure, and integrated manifold designs that support turbochargers for more engine performance from smaller engines.
While these are the three most common types of engine valves, there are many others. For example, sleeve valves are another type that feature a tube or sleeve that sits between the cylinder wall and piston which slide or rotate driven off a camshaft. The movement of the sleeve valve allows ports in the sleeve to align with ports in the cylinder, thereby functioning as a simplified version of an intake and exhaust valve without the complexities of normal configurations. Engine valves are generally specified by six main parameters: stem diameter, stem length, seat angle, valve materials, and coatings.
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