When are two blowdown valves required in a boiler?

Two blowdown valves are required in a boiler when the Maximum Allowable Working Pressure (MAWP) is 100 psi and over. This requirement is based on safety considerations and operational efficiency for high-pressure boilers.

When a boiler operates at higher pressures, the risk associated with the accumulation of impurities and sediments increases significantly. Having two blowdown valves allows for the effective removal of these impurities from the boiler water, ensuring that one valve can be used while the other is closed for maintenance or if issues arise. This redundancy enhances safety by reducing the risk of boiler failure due to improperly managed water quality or pressure imbalances.

In contrast, lower pressure boilers may not necessitate such rigorous requirements, as the implications for safety and operational integrity are less severe. Therefore, the correct answer reflects the critical safety standards established for high-pressure boiler systems, emphasizing the importance of effective blowdown management in maintaining boiler operation.