What happens in a hydraulic circuit when the relief valve opens?

• A. It diverts flow to limit pressure and protect the system.
• B. It increases system pressure.
• C. It blocks all fluid flow.
• D. It cools the hydraulic fluid.

Answer: (A)

Relief valves in hydraulic systems are designed to keep pressure from getting too high by giving hydraulic fluid a safe route back to the reservoir when the pressure reaches a preset limit. When the system pushes against a heavy load or a blockage causes pressure to rise, the relief valve opens and diverts excess flow from the pressure line back to the tank. This bypass reduces the pressure in the circuit, protecting components like seals, hoses, and cylinders from overpressure. The pump keeps delivering flow, but because part of it is redirected, the overall pressure stays near the relief setting. If the load falls off, the valve reseals and normal operation resumes.

This is why it doesn’t increase pressure, block all flow, or directly cool the fluid.