What is the minimum cross-sectional area required when gas pressure relief valves are manifolded?

The minimum cross-sectional area required when gas pressure relief valves are manifolded is determined to ensure that the system can effectively handle the discharge from multiple valves without risking backpressure or inadequate venting. The correct approach is to take the area of the largest vent line and add 50% of the combined areas of the additional vent lines. This calculation ensures that the system is adequately sized to handle potential overpressure situations while also providing safety margins.

This method accounts for the fact that when valves are manifolded, the flow characteristics can change, and additional venting capacity is needed to efficiently release excess pressure. By including the largest area and a percentage of the additional areas, it maintains effective venting efficiency and prevents any bottleneck issues that could occur from relying solely on the largest line.

In contrast, considering only the area of the largest vent line or the combined areas individually doesn't take into account the dynamics of manifolded systems, which could lead to insufficient venting capacity under high-pressure conditions. The correct option thus ensures both adequacy and safety in pressure relief scenarios.