Pressure-vacuum relief valves, as used on tank vessels, are usually set to operate at two points, __________.

Correct Answer: Option C — 14.2 psia; 2 psig

Pressure-vacuum (P/V) relief valves protect cargo tanks from structural damage due to over-pressurization or vacuum collapse. Standard settings are typically 2 psig for pressure and 14.2 psia (approximately -0.5 psig) for vacuum, ensuring the tank atmosphere remains within safe design limits during loading, discharging, or thermal expansion.