Boiler blowdown is water intentionally wasted from a boiler to avoid concentration of impurities during continuing evaporation of steam. The water is blown out of the boiler with some force by steam pressure within the boiler. Bottom blowdown used with early boilers caused abrupt downward adjustment of boiler water level and was customarily expelled downward to avoid the safety hazard of showering hot water on nearby individuals.


Blowdown Valves are designed for continuous use to control the concentration of dissolved solids in boiler water. There are no restrictions on the valve body configuration and only one valve is required. However, the valve must have a valve position indicator accurate to within 0.1 turn of the handwheel. Blowdown valves for intermittent use must meet the requirements and limitations of Blowoff valves described above.

Must read – Why Do We Need A #BlowDown Valve?

A blowoff valve is a pressure release system present in most turbocharged engines. A blowoff valve releases the air into the atmosphere instead of recirculating it. The blowoff action produces a range of distinctive hissing sounds, depending on the exit design. Blowoff valves are used to prevent compressor surge, a phenomenon that readily occurs when lifting off the throttle of an unvented, turbocharged engine. A blowoff valve is connected by a vacuum hose to the intake manifold after the throttle plate. Blowoff valves are designed for applications requiring intermittent operation in order to remove accumulated sediment from equipment, piping or to lower boiler water level in a rapid manner.