The relief valve on a propane cylinder should be located in which space?

• A. Liquid Space
• B. Valve Space
• C. Top Space
• D. Vapor Space

Answer: (D)

Relief valves protect cylinders by venting propane gas when pressure rises. In a propane cylinder, liquid propane sits at the bottom and a space above it contains vapor. When the cylinder heats, some liquid boils and turns into vapor, increasing the pressure in that headspace. The valve needs to release gas quickly as a gas to prevent overpressure, so it’s located in the vapor space at the top where vapor can escape freely. If it were placed in the liquid space, liquid propane could reach the valve and block or delay release, increasing the risk of a overpressure condition.