Refers to engine intake or exhaust valves.
Part of an internal combustion engine. The main purpose of the valve is to allow air in at the proper time (as directed by the cam) and to seal the combustion chamber during the combustion cycle to allow the burning of the air/fuel mixture to create power.
In modern vehicles, the valve is located in the cylinder head, though in small engines and older flat head engines, the valves are located in the block. Valves are actuated by the cam shaft directly or indirectly, depending on the setup.
Valves seal the combustion chamber by having a symbiotic relationship with the valve seat. During the assembly process, each valve is "lapped" with it's associated seat to create a complete seal.
For many late model engines (and performance engines), the intake valves are made of an alloy called “Silchrome 1” (Sil 1) that contains 8.5 percent chromium. Exhaust valves may be made from a martensitic steel with chrome and silicon alloys, or a two- piece valve with a stainless steel head and martensitic steel stem. The intake valve can be made with a hollow stem to save weight. The exhaust valve can be filled with sodium, which turns to liquid and back to solid, which helps with the cooling of the valve. Both of these valve variations are usually used in high-performance applications.
Valves can be actuated directly by the cam shaft as in most overhead cam applications (though there is almost always a lifter in between cam and the valve). Valves can also be indirectly actuated through the use of rocker arms and push rods.