🔍 Key Concepts

• Operation of a hydraulic servo control on a variable-displacement pump (how the manual lever, spool "A", servo piston "B", and feedback link "C" interact) • Effect of internal leakage past the servo piston (B) on the balance of forces in the control system • Whether this design is a self-centering to neutral, runaway to full stroke, or position-holding (follow-up) type control

💭 Think About

• Look at the linkage between the tilting box control arm and the control spool. When the swashplate (tilting box) moves, does that movement tend to return the spool toward neutral, or push it farther off neutral? What does that imply for stability? • Imagine you have set the handle to a certain angle and then let go. As oil slowly leaks past piston B, what must happen inside the control valve ports (D and E) for the handle position and swashplate angle to stay matched? • For each answer choice, ask: if that behavior occurred, would the feedback link (C) and spool (A) still be in balance with the fixed handle position, or would there be an unbalanced force that would move something until a new balance is reached?

✅ Before You Answer

• From the illustration, verify whether link C provides mechanical feedback from the tilting box control arm back to the control spool connected to the handle. • Check whether the control spool at "A" can move relative to the handle when the feedback link moves, or whether it is rigidly fixed—this tells you if the system can automatically correct for leakage past piston B. • For each option, test it against the idea of equilibrium: with the handle fixed, will the forces on piston B and the positions of ports D and E reach a stable balance, or would they keep changing over time?