About Engine-Valves

Engine valves are mechanical components used in internal combustion engines to allow or restrict the flow of fluid or gas to and from the combustion chambers or cylinders during engine operation. Functionally, they perform similarly to many other types of valves in that they block or pass flow, however, they are a purely mechanical device that interfaces with other engine components such as rocker arms in order to open and close in the correct sequence and with the correct timing.

Most engine valves are designed as poppet-style valves because of their up and down popping motion and feature a conical profile valve head that fits against a machined valve seat to seal off the passage of fluids or gases. They are also called mushroom valves because of the distinctive shape of the valve head. Figure 1 shows the nomenclature for the different elements in a typical engine valve.

The two primary elements are the valve stem and the valve head. The head contains a fillet that leads into a seat face that is machined at a specified angle to match the machining of the valve seat to which it will match. The seating of the valve face to the valve seat is what provides the seal for the valve against combustion pressure.
The valve stem connects the valve to the mechanical elements in the engine that operate the valve by creating a force to move the stem against the seating pressure provided by a valve spring. The keeper groove is used to hold the spring in position, and the tip of the valve stem is repeatedly contacted by a rocker arm, tappet, or lifter that actuates the valve.

The cylinder head houses the engine valves. The engine valve’s primary function is to allow air into and out of the cylinder. Air is used to assist in the ignition of the fuel, which pushes the pistons up and down.
Engine valves are classified into two types: intake valves and exhaust valves. Of course, the intake valve allows air to enter and the exhaust valve allows air to exit. The more air you take in and out of the engine, the more efficient it will be thus generating more power. This is why engine valves are so important to engine performance.
The piston in the cylinder moves up and down. The valves are located at the top of the piston stroke. Depending on the manufacturer, the number of valves varies. Because the piston is at the bottom of the cylinder, the intake valve opens to allow air into the cylinder and then closes to make the cylinder airtight in order to establish compression. The exhaust valve will open after the piston has completed the compression and ignition strokes. Then it shuts down. However, you may be wondering how the valve is opened and closed.