Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A): The materials used are frequently different for inlet and exhaust valves.
Reason (R): Inlet valves run cooler than exhaust valves

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Exhaust valves operate in a harsh, oxidizing environment at near-red-hot temperatures, demanding expensive materials like Silchrome or Stellite facings, whereas inlet valves run cool.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Engine valves must seal the combustion chamber and operate reliably under high cyclic stresses and high temperature exposure.

Step 3: Detailed Explanation:
1.

Reason (R): During the intake stroke, the inlet valve is exposed to and cooled by the incoming fresh, cool air-fuel charge (or air alone).
Conversely, the exhaust valve is swept by hot, highly corrosive exhaust gases (temperatures exceeding \(700 ^\circ\text{C}\)) during the exhaust stroke.
Thus, the inlet valve runs significantly cooler than the exhaust valve. Reason (R) is true.
2.

Assertion (A): Because of this extreme temperature difference, exhaust valves require superior, highly expensive heat-resistant alloys (such as austenitic stainless steels or silicon-chromium alloys) to prevent thermal fatigue, oxidation, and warping.
Inlet valves can be constructed from simpler, lower-grade alloy steels. Thus, Assertion (A) is true.
The temperature difference directly explains the necessity of using different, more specialized materials for the exhaust valve. Therefore, (R) is the correct explanation of (A).

Step 4: Final Answer:
The correct option is 1, which corresponds to both statements being true with the Reason correctly explaining the Assertion.