An indication that there is trapped pressure in the hydraulic line is if the cap is not turning easily.

• A. Cap turns freely
• B. Cap is missing
• C. Cap is not turning easily
• D. Oil level is low

Answer: (C)

In hydraulic systems, trapped pressure shows up as resistance when you try to loosen the cap. If the cap is not turning easily, it means pressure is still in the line pushing against it, so opening it could release fluid or cause the cap to pop off unexpectedly. That’s the clear sign that you must depressurize the system before any further work.

If the cap turns freely, there isn’t trapped pressure at the cap, which means the system isn’t pressurized in that area. If the cap is missing, you can’t rely on the cap’s condition to gauge pressure, and attempting service could be dangerous. If the oil level is low, that points to a different issue related to the reservoir’s volume, not necessarily trapped pressure in the line. The key idea is that a cap that doesn’t turn easily indicates pressurized hydraulics.