What is the purpose of a relief valve in a hydraulic system?

• A. To increase system pressure
• B. To filter hydraulic fluid
• C. To shut off flow completely
• D. To limit system pressure by releasing fluid when pressure exceeds a set limit

Answer: (D)

A relief valve safeguards the system by keeping pressure from climbing too high. In operation, the valve stays closed as the pump builds pressure, but when the pressure reaches its preset limit it opens just enough to allow fluid to flow back to the reservoir or another low-pressure path. This bypasses excess fluid and prevents further pressure rise. Once the pressure falls below the limit, the valve closes again and the cycle repeats. This protects hoses, seals, cylinders, and the pump from overpressure and helps maintain a safe, stable operating pressure. It isn’t used to raise pressure, it isn’t a filter, and it doesn’t shut off flow entirely; it only releases enough fluid to keep pressure within safe bounds.