A spur gear pump should be operated with the discharge valves __________.

Correct Answer: Option D — fully opened

Spur gear pumps are positive displacement pumps. Throttling or closing the discharge valve creates excessive pressure, which can cause mechanical failure, casing rupture, or motor overload. To maintain design flow and prevent over-pressurization of the pump casing and piping system, these pumps must always operate with the discharge valve fully opened.