Valves control the flow of fluids or gases within an internal combustion engine, regulating intake of air/fuel mixture and exhaust expulsion. Typically composed of heat-resistant alloys like stainless steel, valves feature a precision-machined face and stem for sealing against valve seats and guides. They are actuated by a camshaft, utilizing mechanical or hydraulic lifters to open and close at precise intervals. Modern engines employ multiple valves per cylinder – often incorporating overhead cam (OHC) or overhead valve (OHV) configurations – to maximize volumetric efficiency. Valve springs maintain closure, while retainers and keepers secure the assembly against rotational forces.