Question 16 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is C **Explanation for C (Trunk):** The **Trunk piston** is characterized by a long skirt (the lower, cylindrical part of the piston body). In modern low-pressure air compressors (and internal combustion engines), the primary function of this long skirt is to act as a crosshead or guide, absorbing and distributing the large lateral (side) forces generated by the connecting rod's angular motion. By having a long contact area with the cylinder walls and liners, the side pressures are spread out over a wide area, reducing localized wear and ensuring stable piston movement. **Why the other options are incorrect:** * **A) Differential:** A differential piston (or stepped piston) has two different diameters and is used to create different pressures or volumes in two separate chambers, often for two-stage compression within a single cylinder. It describes the functional geometry of the piston head, not its ability to distribute side thrust. * **B) Valve-in-head:** "Valve-in-head" (or overhead valve) refers to the design of the cylinder head where the intake and exhaust valves are located. It describes the valve arrangement of the compressor, not the design or function of the piston itself. * **D) Barrel:** "Barrel" is a general descriptive term for a cylindrical shape (like the cylinder itself or the main body of a piston) and is not a specific engineering classification for a piston designed to handle side thrust efficiently, unlike the specialized term "Trunk piston."