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The Function of the Intake Valve and Exhaust Valve in Cars, How They Work and Their Differences

09 April 2025
Fungsi Katup Masuk dan Katup Buang pada Mobil, Cara Kerja dan Perbedaannya

The functions of the exhaust valve and intake valve are closely related to engine performance. If either of these valves has issues, fuel combustion will not be optimal. The intake valve and exhaust valve have different functions and ways of working. Despite these differences, many still do not understand the distinctions between these valves. Instead of being confused, let's pay attention to the following discussion.

Functions of the Intake and Exhaust Valves in Cars

According to their functions, valves are divided into two types: intake valves and exhaust valves. Each of these valves has a different role. The complete explanation is as follows.

Function of the Intake Valve

The intake valve serves as a controller for the flow of fuel and air into the combustion chamber. This valve is responsible for adjusting the ratio of fuel and air according to the needs of the combustion process. 

Function of the Exhaust Valve

Meanwhile, the exhaust valve functions to expel exhaust gas emissions from the remnants of the combustion process in the combustion chamber. 

How the Intake and Exhaust Valves Work

In addition to their different functions, these two valves also have different working mechanisms. As is known, the operation of the valves is heavily dominated by the performance of the cylinder piston. The intake valve will operate when the piston has moved from the top dead center (TDC) to the bottom dead center (BDC). In this condition, the intake valve will draw in fuel and air mixture. Next, the process continues by channeling the air-fuel mixture into the combustion chamber.

On the other hand, the exhaust valve will work when the engine's compression stroke is taking place. In this condition, the piston will move from the bottom dead center (BDC) to the top dead center (TDC). In this condition, the exhaust valve will close so that the combustion process can take place. After the combustion process is complete, the exhaust valve will open again. In this condition, the exhaust valve will expel exhaust gas emissions from the remnants of combustion in the combustion chamber. 

Read Also: Here Are the Parts of a Car Engine, Their Functions, and Images

Differences Between the Intake and Exhaust Valves

After you understand the functions and working mechanisms of the intake and exhaust valves, you need to know other differences between these two valves. The differences are as follows.

1. Size

A striking difference between the intake valve and the exhaust valve can be seen in terms of size. The intake valve has a larger diameter compared to the diameter of the exhaust valve. The larger diameter of the intake valve is intentionally designed to allow the flow of fuel and air mixture to enter the combustion chamber optimally. 

Meanwhile, the diameter of the exhaust valve is intentionally made smaller to facilitate the expulsion of exhaust gases. The ease of the emission gas expulsion process is influenced by the piston’s push. When the expulsion process occurs, the piston will exert high pressure into the combustion chamber so that the exhaust gases can exit easily.

2. Function

The second difference can be seen in terms of function. This has been explained above.

3. Working Mechanism

The third difference can be seen in terms of the working mechanism.

4. Valve Markings

The fourth difference can be seen in the markings on the valves. The intake valve is marked with the word “in”. Meanwhile, the exhaust valve is marked with the word “ex”. 

5. Material

The last difference can be seen in terms of the material used. The intake valve is made from metal containing magnetic elements. Meanwhile, the exhaust valve is made from a combination of steel and nickel.

Considering the important roles of the intake and exhaust valves, it is essential to regularly check the condition of these components. If there are issues with these components, visit a Daihatsu workshop immediately for the best car service and maintenance. 

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