The relief valve for a low pressure steam system should be set at:

In a low pressure steam system, the relief valve is a crucial safety device designed to protect the system from excessive pressure. The correct setting for a relief valve in this context is typically at or slightly above the system's operating pressure to ensure safe operation.

The setting of 15 psig is appropriate for low pressure steam systems because it aligns with industry standards that define low pressure steam as operating typically below 15 psig. This ensures that the relief valve will open to prevent pressure from exceeding a safe threshold, thereby preventing potential hazards such as equipment damage or failure.

Options like 14.7 psia or 30 psia represent pressures that don't align with the standard operating range for low pressure systems. Setting the relief valve at 30 psig would be unnecessarily high for low pressure applications, risking the system's safety by allowing pressures to reach levels that could cause damage before the valve activates. Therefore, 15 psig is the optimal choice for maintaining safety and operational integrity in low pressure steam systems.