Intake valves refer to a type of engine component that allows air and fuel mixture into an internal combustion engine's cylinder during the intake stroke. These valves are usually located on either side of the cylinder head, and they open in response to pressure from the crankcase or the exhaust system when the piston moves downward during the intake stroke. Once opened, the intake valve allows air-fuel mixture to enter the combustion chamber through a port, which is connected to an intake manifold that draws in fresh air and fuel from outside of the engine. After the intake event has occurred, the intake valve closes to seal off the cylinder again until the next cycle begins.