Pilot-operated relief valves have a third port that may be used to __________.

• A. Unload the pump
• B. Vent the relief
• C. Remotely operate the relief
• D. All of the above

Answer: (D)

Pilot-operated relief valves use a small control path to govern the larger relief action, and that extra port is a flexible control opportunity. The third port can be used to unload the pump by routing excess flow back to the reservoir when full system pressure isn’t needed, which reduces pump work and wear. It can also be vented or connected to a separate drain line so the relief can vent to atmosphere or to a safe drain when the valve opens. Additionally, this port provides a path for remote actuation: a control signal from another part of the system (manual, solenoid, or another hydraulic circuit) can apply pilot pressure to open or hold the relief, enabling remote control of relief events. Because it supports unloading, venting, and remote operation, the third port enables all of these functions.