🔍 Key Concepts

• compressibility of air vs. incompressibility of hydraulic fluid • what happens to trapped air when pressure increases and then the actuator starts to move • relationship between system operating pressure and changes in air volume/pressure

💭 Think About

• When a hydraulic system first builds pressure, what happens to any air bubbles mixed with the fluid before the actuator starts to move? • As the actuator begins to move and the load starts to shift, what happens to the pressure on those air bubbles and how does that affect their volume? • How could repeated cycles of compression and expansion of trapped air create an on‑off, jerky motion instead of smooth, continuous movement?

✅ Before You Answer

• Remember that liquids are nearly incompressible but gases are highly compressible—which choices correctly use that idea? • Eliminate any options that claim benefits that are opposite of what air actually does in hydraulic systems (e.g., better load movement or better lubrication). • Focus on the answer that describes repeated compression and re‑expansion of air at around the normal operating pressure of the system, not some unrealistic extreme.