Which symptom signals the hydraulic system may be experiencing air intrusion?

• A. No change in performance.
• B. Spongy or inconsistent cylinder movement, foamy fluid, or air entering via a leak.
• C. Cylinders move faster than normal.
• D. Ticks and noises only.

Answer: (B)

Air in the hydraulic fluid changes how the system responds because the fluid becomes compressible. When air is present, cylinder movement tends to feel spongy and inconsistent as the trapped air is compressed and released during operation. Foamy fluid is another telltale sign because air bubbles create the foam you can see in the reservoir or hoses. Air can enter the system through leaks, drawing air in along the lines or seals, which then disrupts pressure and smooth operation.

The other signs don’t fit air intrusion as reliably: if nothing changes in performance, the system is likely not affected by air; moving faster than normal usually points to excessive flow or a pump/valve issue rather than trapped air; and ticks or noises alone can arise from many mechanical causes and aren’t specific to air in the hydraulic circuit.