🔍 Key Concepts

• Pressure-vacuum relief valves purpose on tank vessels (protecting cargo tanks from overpressure and excessive vacuum) • Typical pressure setting (psig) and vacuum setting (inches of water or inches of vacuum) used in cargo tank protection systems • Relationship of settings to atmospheric pressure (psia) and structural limits of the tank

💭 Think About

• Which option shows one value clearly related to vacuum and one value clearly related to positive pressure? • Think about whether these valves are intended to open only when pressure is above atmospheric, only when below atmospheric, or at both conditions. • Which units and magnitudes look realistic for protecting thin‑plated cargo tanks from damage during loading, discharging, or thermal expansion/contraction?

✅ Before You Answer

• Be sure one setting is for vacuum protection (tank being sucked in) and one is for overpressure protection (tank bulging out). • Check that the units make sense: psia vs psig vs inches of vacuum – which are normally used for vacuum vs pressure on tank vents? • Verify that the chosen values are practical for tank structure (not so high that the tank would fail, not so low that the valve is always lifting).