Definition - What does Blowdown Valve mean?
Blowdown valves are useful in fossil fuel fired boilers for continuous or intermittent use to drain dissolved solids from the boiler water. These valves are fitted on the drain lines of the boilers. Generally only one blowdown valve is used in the boilers; however, the use of multiple blowdown valves in a boiler depends on the design and purpose of the boiler.
Corrosionpedia explains Blowdown Valve
Blowdown valves are commonly used to control the concentration of dissolved solids in the boiler water. The valves are designed and manufactured according to the requirements of the boiler and the industrial application. If a boiler makes use of more than one blowdown valves, then these two valves are often used in series to minimize erosion. Here, one valve acts as a sealing valve, and the other valve acts as a blowdown valve. The sealing valve is customarily opened first and closed last. To minimize the erosion on the disk faces and the seats, both of the valves are opened simultaneously and rapidly. Most importantly, during blow down care is taken to avoid trapping rust particles within the valve. This is done by reopening a valve again so that any remaining rust particles are flushed out with the next passage of steam through the pipe. Bottom blowdown valves are often rebuilt or replaced whenever the boiler is taken out of service for maintenance.