Under what condition must a boiler have two bottom blowdown valves?

A boiler must have two bottom blowdown valves when the pressure exceeds 100 psi due to safety and operational efficiency reasons. At higher pressures, the potential for sediment and impurities to accumulate in the bottom of the boiler increases, which can lead to reduced performance and possibly dangerous conditions if not properly managed.

The requirement for having a second blowdown valve allows for redundancy in the system. This means that if one valve fails or requires maintenance, the other is still operational, enabling continued safe operation of the boiler. Additionally, the dual valves help in more effectively removing sludge and sediment build-up, thus maintaining water quality and ensuring that the boiler operates at optimal efficiency.

This standard is particularly important at higher pressures where the risks associated with improper blowdown procedures can be significantly more severe. Therefore, the requirement to have two bottom blowdown valves at pressures above 100 psi reflects the need for enhanced safety and operational integrity.