Boilers have 2 bottom blowdowns when the MAWP exceeds what pressure?

Boilers are equipped with bottom blowdown valves primarily to remove sediment and sludge that accumulate at the bottom of the boiler and to maintain water quality. The requirement for having two bottom blowdowns is linked to the potential risk associated with higher-pressure operations.

When the maximum allowable working pressure (MAWP) of a boiler exceeds 100 psi, it is deemed necessary to have two bottom blowdowns. This is a safety measure aimed at improving the reliability of the blowdown process. In the event that one blowdown valve becomes inoperative or is under maintenance, the second blowdown provides an alternative means of ensuring that the boiler remains safe and operational.

At pressures below 100 psi, a single blowdown system is generally adequate as the risks associated with sediment buildup and water quality are less severe. Therefore, the specific threshold of 100 psi reflects industry standards and safety practices that ensure high-pressure boilers operate safely and effectively. This requirement acknowledges that as the operation pressure increases, so too does the need for redundant safety measures to protect the equipment and personnel.