What is the function of a hydraulic relief (safety) valve?

• A. To filter contaminants from the hydraulic fluid.
• B. To increase flow rate to actuator.
• C. To limit system pressure to a safe maximum by venting fluid.
• D. To cool the hydraulic fluid.

Answer: (C)

Relief valves act as safety devices that prevent overpressurizing a hydraulic system. They stay closed during normal operation, but when system pressure reaches a preset limit, the valve opens and allows fluid to bypass back to the reservoir or into the pump inlet. This dumps enough fluid to keep the overall pressure from climbing higher, protecting hoses, seals, actuators, and other components from damage. Once the pressure falls below the setting, the valve closes again and normal operation resumes. The set pressure is adjustable to match the system’s safe maximum.

Filtration is done by filters, not relief valves. Increasing flow to an actuator is handled by flow-control components or the pump, not by the relief valve. Cooling is accomplished by heat exchangers or cooling systems, not relief valves.