Which valve is normally open with sensing at the output side?

• A. Pressure valve
• B. Pressure regulating valve
• C. Aeration
• D. Pressure relief valve (correct)

Answer: (D)

Understanding how a valve responds to pressure on the outlet side is key. A pressure relief valve is designed to protect the downstream side of the system by sensing the pressure after the valve (the output side) and opening to dump flow back to the reservoir when that outlet pressure reaches a preset limit. This prevents overpressure from damaging downstream components like hoses, cylinders, or other equipment. The other options play different roles: a pressure valve or a pressure regulating valve focuses on setting and maintaining a downstream pressure without venting excess flow, while an aeration valve handles air release or introduction. Because the device whose primary purpose is to relieve excess downstream pressure based on output-side sensing is the pressure relief valve, it is the best answer.