A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways.
Valve is a device to close and open a passage. In motor vehicle engines, two engine valves are used for each cylinder-an inlet (or intake) valve and an exhaust valve. Fuel is allowed to the cylinder by the inlet valve. When closed, the valve seals the combustion space tightly.