What is the function of a relief valve in a hydraulic circuit?

• A. To increase system pressure indefinitely.
• B. To cool the hydraulic fluid.
• C. To filter contaminants.
• D. To limit system pressure by diverting flow when pressure exceeds the set point.

Answer: (D)

Relief valves protect a hydraulic system by preventing overpressure. They are designed to open once the system pressure reaches a pre-set value, allowing fluid to flow back to the tank or reservoir. This diversion stops pressure from climbing higher and protects components like seals, hoses, and actuators from damage. The valve is usually spring-loaded and adjustable, so you can set the maximum pressure the system should see.

This isn’t about increasing pressure, cooling fluid, or filtering contaminants. Increasing pressure indefinitely would damage components, cooling is handled by heat exchangers or cooling circuits, and filtering is done by filters. The relief valve’s job is simply to cap pressure and relieve excess flow when the set point is exceeded.