Which device should be placed at the discharge of a positive displacement pump to protect the system?

• A. Relief Valve
• B. Check Valve
• C. Gate Valve
• D. Globe Valve

Answer: (A)

The main idea here is protection against overpressure. A positive displacement pump delivers a specific volume with each cycle, so if the discharge is blocked or flow is restricted, pressure in the system can rise rapidly and reach dangerous levels. A relief valve placed on the discharge line opens at a set pressure to vent excess fluid back to the reservoir or suction, preventing damage to the pump, piping, and components. This keeps the system within its design pressure limits even if flow is momentarily restricted.

The other devices don’t provide this protective function. A check valve prevents backflow but won’t limit pressure if the discharge is blocked. Gate and globe valves are isolation valves used to start/stop flow, not to protect the system from overpressure. They can even worsen conditions if the pump dead-heads against a closed valve, whereas a relief valve actively relieves pressure.

So, the relief valve is the device that protects the system by limiting discharge pressure.