Which value represents the upper bound of the normal hydraulic reservoir quantity percentage?

• A. 85%
• B. 90%
• C. 80%
• D. 75%

Answer: (A)

In hydraulic systems the reservoir isn’t filled to full capacity because oil expands with temperature and air must have space to compress and vent. The upper bound is simply the highest fill level that is still considered normal and safe, giving enough room for expansion without risking overflow or foaming. Filling to this top end keeps the system able to handle heat rise and cycling without spilling, while going higher reduces that headroom and increases the chance of overflow or air entrainment. A value at the top end of the normal range is therefore the one that represents the upper bound.