How Do Engine Valves Work?

Considered mechanical components, engine valves enable or limit the flow of fluid or gas to and from the cylinders or combustion chambers during engine operation. Like other types of valves, they block or allow flow; however, they are exclusively designed to interface with other engine components, such as rock arms. To better understand how they work, this blog will provide a comprehensive overview of engine valves.

Housed by the cylinder head, the primary function of engine valves is to allow air into and out of the cylinder. Air is utilized to ignite the fuel, pushing the pistons up and down. Apart from what engine valves are intended to do, they can be classified into two types: intake valves and exhaust valves. Intake valves allow air to enter, whereas exhaust valves allow air to exit. Please note that the more air you take in and out of the engine, the more efficient it is; thus, it can generate more power.

In general, the piston in the cylinder moves up and down. Meanwhile, the valves are situated at the top of the piston stroke. Keep in mind that the number of valves varies according to manufacturer. Due to the fact that the piston is at the bottom of the cylinder, the intake valve opens to allow air into the cylinder. Then, it closes to establish compression. The exhaust valve, on the other hand, only opens after the piston has completed the compression and ignition strokes. Once this is done, it shuts down.

Various Components of an Engine Valve

Because of the up and down popping motion, most engine valves are designed like poppet-style valves, meaning that they have a conical profile valve head that fits against a machined valve seat to close off the passage of fluids or gasses. As a result of their unique shape, they are often called mushroom valves. Beyond this structure, they are made of a few key components that we will outline below.

Of all the components that make up engine valves, the valve stem and valve head are the two most important. The head has a filet that leads to a seat face machined at an angle to mate with the valve seat it will be affixed to. The seating of the valve face with the valve seat is what creates the seal for the valve against combustion pressure.

By providing force to move the stem against the seating pressure produced by a valve spring, the valve stem links the valve to the internal mechanisms within the engine that operate the valve. Meanwhile, the spring is held securely by the keeper groove, and the valve is actuated by a rocker arm, tappet, or lifter repeatedly contacting the tip of the valve steam.

How Do Engine Valves Work?

Engine valves follow a series of key steps to function properly, those of which we will list in this section.

  1. The engine’s crankshaft receives initial power and drives the camshaft.
  2. During the suction stroke, the camshaft moves and pushes the inlet valve down.
  3. Due to the spring force, the camshaft enables the inlet valve to close when the piston follows the compression stroke.
  4. After the compression stroke, the piston transitions into the power stroke with both valves closed.
  5. Following the power stroke, the exhaust stroke occurs, wherein the camshaft pushes and opens the exhaust valve.
  6. Finally, the piston pushes the exhaust fumes out, and the cycle repeats itself.

Types of Engine Valves

Beyond engine valves being classified as either intake or exhaust valves, there are also various types of engine valves based on design and materials. The following are the most common types:

  • Monometallic engine valves are usually made of a single material for both the valve steam and the valve head. These engine valves will frequently have anti-friction properties and strong heat resistance.
  • Bimetallic engine valves, also called bimetal engine valves, are manufactured by friction welding two distinct materials together. This generates a valve with austenitic steel for the head and martensitic steel for the stem. The austenitic steel provides high-temperature resistance and corrosion resistance, while martensitic steel provides high tensile strength and abrasive wear resistance.
  • Hollow engine valves are a type of bimetallic valve designed with a sodium-filled hollow chamber. The hollow shape of the valve allows for more heat transfer via the stem and is better suited for modern engines that require more power from smaller, denser engine designs.


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January 12, 2023

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