What is the purpose of relief valves and load-sensing valves in hydraulic circuits?

• A. Relief valves regulate system color-coding and labeling.
• B. Relief valves protect against overpressure; load-sensing valves adjust flow/pressure to match demand, improving efficiency and reducing heat.
• C. Load-sensing valves regulate temperature; relief valves filter contaminants.
• D. Relief valves store energy; load-sensing valves lock flow.

Answer: (B)

In hydraulic circuits, managing pressure and flow is essential for safety and efficiency. Relief valves act as safety devices that open when system pressure climbs above a set limit, allowing fluid to return to the reservoir. This prevents damage to pumps, hoses, and actuators by keeping pressure within safe bounds.

Load-sensing valves, on the other hand, adjust the delivered flow and pressure to match what the load actually needs. They sense the demand at the actuators and modulate the circuit so only the required pressure and flow are produced, which reduces energy use and minimizes heat generation in the fluid. This makes multi-actuator systems more efficient because the pump isn’t wasting energy pushing pressure higher than necessary.

The other options mix up these roles: relief valves aren’t about color-coding or filtration, and load-sensing isn’t primarily about temperature regulation or locking flow.