When the maximum allowable working pressure of a boiler exceeds which pressure, two bottom blowoff valves are required?

In the context of boiler safety and design, the requirement for two bottom blowoff valves is specifically linked to the potential hazards associated with higher pressure systems. When the maximum allowable working pressure of a boiler exceeds 100 psig, the rationale for needing two blowoff valves becomes critical for ensuring safe operation and effective maintenance.

The reason behind this regulation is primarily to mitigate the risk of failure or malfunction of a single blowoff valve, which could lead to dangerous conditions, such as uncontrolled pressure buildup or improper evacuation of sediment and scale. By requiring two valves, it allows for redundancy—ensuring that even if one valve fails or requires maintenance, the other can remain operational to maintain proper system integrity. This approach aligns with safety practices and codes that prioritize risk management in high-pressure environments.

In summary, exceeding 100 psig necessitates the additional layer of safety afforded by having two bottom blowoff valves, ultimately contributing to the safe operation and longevity of boiler systems.