An intake valve is the name for a valve that allows air or fluid to pass through it, typically during the intake phase of an engine's operation. The most common example is found inside a typical modern day car engine, also known as an internal combustion engine. The valves allow an air and fuel mixture into the engine's cylinders, where it can then be compressed. They shut during the compression phase and the spark plug ignites the air and fuel mixture, creating a force that propels the car forward.
Two valves are used in each cylinder of the car engine. The intake valve's designated purpose it to open and close in time to let the right amount of air/fuel mixture in. The second valve in the cylinder is known as the exhaust valve. It is almost identical to the intake, except its purpose is to let the air out after combustion has taken place instead of letting it in.
If these valves do not close or open properly, problems can occur. The engine will create less power and the car will not move as quickly. Not only can this damage the engine over time, it also hurts the gas mileage since the car is consuming more gas and yet creating less power than normal at the same time.
The most common valve type used for an intake valve is the poppet valve. It's also referred to as a mushroom valve because of its shape: it looks like an elongated mushroom with a large head that blocks the entrance to the cylinder and an attached stem for moving the head. When the head is moved, air can pass around it, but when the head blocks the cylinder, it fits snugly like a plug to prevent any more air from coming in.
Location of the intake and exhaust valves in a car engine can vary. Many have both valves situated at the top of the cylinder, while other engines may put the valves on the sides. The valves can also be in a combination with one valve on the top of the cylinder and the other located on the side.