What is the normal hydraulic reservoir quantity?

• A. 45-85%
• B. 40-80%
• C. 50-90%
• D. 30-60%

Answer: (A)

The number to remember is a mid-to-high range that leaves space for fluid expansion and air separation while still keeping a solid fluid reserve. In hydraulic systems, fluid expands with temperature and demand, so having some headroom in the reservoir prevents overflow and maintains proper pump prime. At the same time, you don’t want the reservoir filled to the brim, because there needs to be enough liquid available for the pump to draw from and for the system to handle leaks or sudden demands. A typical guideline of about 45-85% of the reservoir’s capacity achieves this balance, providing sufficient expansion space and a reliable supply.

The other ranges are either too restrictive or too close to full, risking insufficient headspace for expansion or, conversely, too much risk of overflow and air ingestion when temperatures rise or the system operates under high demand.