How many safety relief valves are required for a boiler with bare tube heating surface exceeding 500 ft²?

For a boiler with bare tube heating surfaces that exceed 500 square feet, the requirement is to have at least two safety relief valves. This regulation is in place to ensure adequate protection against overpressurization, which could lead to catastrophic failures. The rationale behind having multiple safety relief valves is that each valve serves as a backup for the other; if one valve fails to operate correctly, the second valve can still provide the necessary pressure relief, thereby enhancing the overall safety of the boiler system.

Additionally, having more than one valve can help distribute the relieving capacity, which can mitigate the risk of pressure surges. This is particularly relevant in larger boilers where the potential for accumulating harmful pressure is significant. Therefore, in scenarios where the heating surface exceeds 500 square feet, it is crucial to install at least two safety relief valves to comply with safety standards and regulations effectively.