What is the primary purpose of the relief valve on a cargo pump?

The correct choice highlights the primary function of the relief valve on a cargo pump, which is to permit the return of cargo to the suction side of the pump. This is crucial for maintaining safe operating conditions within the pump system. When the discharge pressure exceeds a predetermined level, the relief valve opens and allows some of the cargo to flow back to the suction side, preventing excessive pressure buildup that could cause damage to the pump or associated piping.

By enabling cargo to return to the suction side, it effectively acts as a safety mechanism, ensuring that the system can regulate pressures and avoid potential failures. This helps maintain steady flow rates and operational efficiency within the pumping system while also protecting against over-pressurization.

In contrast, other choices do not accurately describe the primary function of the relief valve. Increasing pressure on the discharge side, for example, is not the role of the relief valve; instead, it actively works to control and reduce pressure when necessary. Preventing motor overload is also a separate concern usually handled by motor protection devices. Lastly, while discharging excess cargo automatically may seem relevant, it's not the function of the relief valve; rather, it's primarily about managing pressure within the system.