Question 38 1AE01 - First Assistant Engineer

The Correct Answer is D. ### Explanation for D (The cushion adjustment needle valve is not open sufficiently) The function of a hydraulic cylinder cushion is to slow the piston just before the end of its stroke by restricting the flow of exhaust oil. This restriction is managed by a cushion spear entering a fixed cushion bushing, forcing the exhausting oil through a bypass line controlled by an adjustable needle valve. If the piston **abruptly slows** (decelerates too quickly), it indicates that the restriction to the exhaust flow is too high. If the restriction is too high, the pressure builds up excessively, forcing the piston to a near halt. If the valve is **not open sufficiently**, the bypass path is too narrow, leading to this excessive restriction and the sudden, harsh deceleration. Once the high pressure dissipates or the force overcomes the pressure (often relying on leakage or a very slow metered flow through the tiny opening), the piston pressure differential is eventually re-established, allowing the piston to **creep** (move slowly) to the absolute end of its stroke until the spear fully exits the cushion bushing. ### Why the other options are incorrect: **A) The rod wiper is jammed in the cushion spear.** The rod wiper is located near the rod end gland and prevents contaminants from entering the cylinder along the rod surface. It has no physical interaction with the internal cushion spear or the cushioning process, which occurs internally at the cushion bushing. This scenario would likely cause damage or wear on the rod, not affect the internal cushioning dynamics. **B) The exhaust oil is flowing freely through the cushion nose.** If the exhaust oil were flowing freely, there would be no significant restriction. This would result in the cylinder **not slowing down at all** (or slowing down very little), causing a hard, damaging impact at the end of the stroke, which contradicts the described symptom of the piston abruptly slowing and creeping. **C) The cushion adjustment needle valve is open too far.** If the needle valve is open too far, the flow path is minimally restricted, which is essentially the same outcome as B. The cylinder would fail to cushion effectively, resulting in a damaging impact at the end of the stroke, not an abrupt stop followed by creeping.