Question 20

The Correct Answer is B. **Explanation for Option B (suction side of pump):** The primary function of a cargo pump relief valve is to protect the pump casing, associated piping, and the prime mover (motor or turbine) from excessive pressure buildup, which typically occurs if the discharge valve is accidentally closed while the pump is running. When the relief valve opens, it diverts the pressurized fluid away from the discharge side. Routing this fluid back to the **suction side of the pump** (or sometimes back to the cargo tank, which is hydraulically the same concept as the pump suction) allows the pressure to be safely relieved without losing the cargo. This design ensures that the pump continues to circulate the fluid within a closed, low-pressure loop until the discharge blockage is corrected. **Explanation of Incorrect Options:** **A) cargo pump pressure gauge:** The relief valve is a safety mechanism for flow and pressure management, not a component related to measurement or instrumentation. Piping the relief line to the pressure gauge would serve no protective purpose and would likely damage the gauge. **C) atmosphere through pump vent:** Pumping flammable or toxic liquid cargo (like petroleum products or chemicals) directly to the atmosphere is extremely dangerous, illegal, and environmentally hazardous. Pump vents are typically small openings used for air release (venting during startup) or sealing drainage, not for managing large-volume pressure relief flow. **D) crossover line:** While a crossover line connects different parts of the cargo piping system (e.g., connecting two separate manifolds), it is still part of the *discharge* network. If the excessive pressure condition is caused by a blockage downstream (like a closed discharge valve), piping the relief flow to the crossover line would often not solve the overpressure problem, as the entire discharge system would remain pressurized. The safe, low-pressure alternative is always the suction side/tank.