Under what pressure is it permissible to have one blowdown valve on a boiler?

The correct answer is based on the general industry practice regarding boiler safety and design criteria. A single blowdown valve can be used on a boiler operating at 100 psi or lower pressure. This is important because as the pressure increases, the potential for hazards and the requirements for safety become stricter.

When operating at pressures above this level, having more than one blowdown valve is advisable to ensure safety, efficient operation, and proper maintenance. At 100 psi, it remains manageable while still allowing for effective removal of sludge and sediment that can accumulate in the boiler.

Overall, using a single blowdown valve at this level of pressure aligns with the safety and operational standards typically observed in the industry, helping to prevent potential issues related to pressure management in steam systems.